How should the ViewModel close the form

Question

I m trying to learn WPF and the MVVM problem  but have hit a snag  This question is similar but not quite the same as this one  handling-dialogs-in-wpf-with-mvvm     I have a  quot Login quot  form written using the MVVM pattern  This form has a ViewModel which holds the Username and Password  which are bound to the view in the XAML using normal data bindings  It also has a  quot Login quot  command which is bound to the  quot Login quot  button on the form  agan using normal databinding  When the  quot Login quot  command fires  it invokes a function in the ViewModel which goes off and sends data over the network to log in  When this function completes  there are 2 actions   The login was invalid - we just show a MessageBox and all is fine  The login was valid  we need to close the Login form and have it return true as its DialogResult      The problem is  the ViewModel knows nothing about the actual view  so how can it close the view and tell it to return a particular DialogResult   I could stick some code in the CodeBehind  and or pass the View through to the ViewModel  but that seems like it would defeat the whole point of MVVM entirely     Update In the end I just violated the  quot purity quot  of the MVVM pattern and had the View publish a Closed event  and expose a Close method  The ViewModel would then just call view Close  The view is only known via an interface and wired up via an IOC container  so no testability or maintainability is lost  It seems rather silly that the accepted answer is at -5 votes  While I m well aware of the good feelings that one gets by solving a problem while being  quot pure quot   Surely I m not the only one that thinks that 200 lines of events  commands and behaviors just to avoid a one line method in the name of  quot patterns quot  and  quot purity quot  is a bit ridiculous

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The way I would handle it is to add an event handler in my ViewModel  When the user was successfully logged in I would fire the event  In my View I would attach to this event and when it fired I would close the window

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Here s what I initially did  which does work  however it seems rather long-winded and ugly  global static anything is never good   1  App xaml cs  public partial class App   Application          create a new global custom WPF Command     public static readonly RoutedUICommand LoggedIn   new RoutedUICommand        2  LoginForm xaml     bind the global command to a local eventhandler  lt CommandBinding Command  client App LoggedIn  Executed  OnLoggedIn    gt    3  LoginForm xaml cs     implement the local eventhandler in codebehind private void OnLoggedIn  object sender  ExecutedRoutedEventArgs e         DialogResult   true      Close        4  LoginFormViewModel cs     fire the global command from the viewmodel private void OnRemoteServerReturnedSuccess         App LoggedIn Execute this  null         I later on then removed all this code  and just had the LoginFormViewModel call the Close method on it s view  It ended up being much nicer and easier to follow  IMHO the point of patterns is to give people an easier way to understand what your app is doing  and in this case  MVVM was making it far harder to understand than if I hadn t used it  and was now an anti-pattern

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FYI  I ran into this same problem and I think I figured out a work around that doesn t require globals or statics  although it may not be the best answer   I let the you guys decide that for yourself   In my case  the ViewModel that instantiates the Window to be displayed  lets call it ViewModelMain  also knows about the LoginFormViewModel  using the situation above as an example      So what I did was to create a property on the LoginFormViewModel that was of type ICommand  Lets call it CloseWindowCommand   Then  before I call  ShowDialog   on the Window  I set the CloseWindowCommand property on the LoginFormViewModel to the window Close   method of the Window I instantiated   Then inside the LoginFormViewModel all I have to do is call CloseWindowCommand Execute   to close the window   It is a bit of a workaround hack I suppose  but it works well without really breaking the MVVM pattern   Feel free to critique this process as much as you like  I can take it

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Create a Dependency Property in your View any UserControl or Window you want to close   Like below    public bool CloseTrigger                       get   return  bool GetValue CloseTriggerProperty                 set   SetValue CloseTriggerProperty  value                        public static readonly DependencyProperty CloseTriggerProperty               DependencyProperty Register  CloseTrigger   typeof bool   typeof ControlEventBase   new PropertyMetadata new PropertyChangedCallback OnCloseTriggerChanged              private static void OnCloseTriggerChanged DependencyObject dp  DependencyPropertyChangedEventArgs e                          write Window Exit Code             And bind it from your ViewModel s property    lt Window x Class  WpfStackOverflowTempProject MainWindow          xmlns  http   schemas microsoft com winfx 2006 xaml presentation          xmlns x  http   schemas microsoft com winfx 2006 xaml          Title  MainWindow   Width  525          CloseTrigger   Binding Path CloseWindow Mode TwoWay     Property In VeiwModel   private bool closeWindow       public bool CloseWindow               get   return closeWindow            set                         closeWindow   value              RaiseChane  CloseWindow                      Now trigger the close operation by changing the CloseWindow value in ViewModel

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Ok  so this question is nearly 6 years old and I still can t find in here what I think it s the proper answer  so allow me to share my  2 cents      I actually have 2 ways of doing it  first one is the simple one   the second on the right one  so if you are looking for the right one  just skip  1 and jump to  2   1  Quick and Easy  but not complete   If I have just a small project I sometimes just create a CloseWindowAction in the ViewModel           public Action CloseWindow   get  set       In MyViewModel cs   And whoever crates the View  or in the View s code behind I just set the Method the Action will call    remember MVVM is about separation of the View and the ViewModel   the View s code behins is still the View and as long as there is proper separation you are not violating the pattern   If some ViewModel creates a new window   private void CreateNewView         MyView window   new MyView        window DataContext   new MyViewModel                                                                 CloseWindow   window Close                                       window ShowDialog        Or if you want it in your Main Window  just place it under your View s constructor   public MyView         InitializeComponent                   this DataContext   new MainViewModel                                                              CloseWindow   this Close                                   when you want to close the window  just call the Action on your ViewModel     2  The right way  Now the proper way of doing it is using Prism  IMHO   and all about it can be found here   You can make an Interaction Request  populate it with whatever data you will need in your new Window  lunch it  close it and even receive data back  All of this encapsulated and MVVM approved  You even get a status of how the Window was closed  like if the User Canceled or Accepted  OK button  the Window and data back if you need it  It s a bit more complicated and Answer  1  but it s a lot more complete  and a Recommended Pattern by Microsoft   The link I gave have all the code snippets and examples  so I won t bother to place any code in here  just read the article of download the Prism Quick Start and run it  it s really simple to understad just a little more verbose to make it work  but the benefits are bigger than just closing a window

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Ok  so this question is nearly 6 years old and I still can t find in here what I think it s the proper answer  so allow me to share my  2 cents      I actually have 2 ways of doing it  first one is the simple one   the second on the right one  so if you are looking for the right one  just skip  1 and jump to  2   1  Quick and Easy  but not complete   If I have just a small project I sometimes just create a CloseWindowAction in the ViewModel           public Action CloseWindow   get  set       In MyViewModel cs   And whoever crates the View  or in the View s code behind I just set the Method the Action will call    remember MVVM is about separation of the View and the ViewModel   the View s code behins is still the View and as long as there is proper separation you are not violating the pattern   If some ViewModel creates a new window   private void CreateNewView         MyView window   new MyView        window DataContext   new MyViewModel                                                                 CloseWindow   window Close                                       window ShowDialog        Or if you want it in your Main Window  just place it under your View s constructor   public MyView         InitializeComponent                   this DataContext   new MainViewModel                                                              CloseWindow   this Close                                   when you want to close the window  just call the Action on your ViewModel     2  The right way  Now the proper way of doing it is using Prism  IMHO   and all about it can be found here   You can make an Interaction Request  populate it with whatever data you will need in your new Window  lunch it  close it and even receive data back  All of this encapsulated and MVVM approved  You even get a status of how the Window was closed  like if the User Canceled or Accepted  OK button  the Window and data back if you need it  It s a bit more complicated and Answer  1  but it s a lot more complete  and a Recommended Pattern by Microsoft   The link I gave have all the code snippets and examples  so I won t bother to place any code in here  just read the article of download the Prism Quick Start and run it  it s really simple to understad just a little more verbose to make it work  but the benefits are bigger than just closing a window

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I implemented Joe White s solution  but ran into problems with occasional  DialogResult can be set only after Window is created and shown as dialog  errors   I was keeping the ViewModel around after the View was closed and occasionally I later opened a new View using the same VM   It appears that closing the new View before the old View had been garbage collected resulted in DialogResultChanged trying to set the DialogResult property on the closed window  thus provoking the error   My solution was to change DialogResultChanged to check the window s IsLoaded property   private static void DialogResultChanged      DependencyObject d      DependencyPropertyChangedEventArgs e        var window   d as Window      if  window    null  amp  amp  window IsLoaded          window DialogResult   e NewValue as bool       After making this change any attachments to closed dialogs are ignored

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Here is the simple bug free solution  with source code   It is working for me    Derive your ViewModel from INotifyPropertyChanged Create a observable property CloseDialog  in ViewModel  public void Execute            Do your task here         if task successful  assign true to CloseDialog     CloseDialog   true     private bool  closeDialog  public bool CloseDialog       get   return  closeDialog        set    closeDialog   value  OnPropertyChanged         public event PropertyChangedEventHandler PropertyChanged   private void OnPropertyChanged  CallerMemberName string property             if  PropertyChanged    null                PropertyChanged this  new PropertyChangedEventArgs property                   Attach a Handler in View for this property change       loginDialogViewModel   new LoginDialogViewModel        loginPanel DataContext    loginDialogViewModel       loginDialogViewModel PropertyChanged    OnPropertyChanged   Now you are almost done  In the event handler make DialogResult   true   protected void OnPropertyChanged object sender  PropertyChangedEventArgs args        if  args PropertyName     CloseDialog                 DialogResult   true

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FYI  I ran into this same problem and I think I figured out a work around that doesn t require globals or statics  although it may not be the best answer   I let the you guys decide that for yourself   In my case  the ViewModel that instantiates the Window to be displayed  lets call it ViewModelMain  also knows about the LoginFormViewModel  using the situation above as an example      So what I did was to create a property on the LoginFormViewModel that was of type ICommand  Lets call it CloseWindowCommand   Then  before I call  ShowDialog   on the Window  I set the CloseWindowCommand property on the LoginFormViewModel to the window Close   method of the Window I instantiated   Then inside the LoginFormViewModel all I have to do is call CloseWindowCommand Execute   to close the window   It is a bit of a workaround hack I suppose  but it works well without really breaking the MVVM pattern   Feel free to critique this process as much as you like  I can take it

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I implemented Joe White s solution  but ran into problems with occasional  DialogResult can be set only after Window is created and shown as dialog  errors   I was keeping the ViewModel around after the View was closed and occasionally I later opened a new View using the same VM   It appears that closing the new View before the old View had been garbage collected resulted in DialogResultChanged trying to set the DialogResult property on the closed window  thus provoking the error   My solution was to change DialogResultChanged to check the window s IsLoaded property   private static void DialogResultChanged      DependencyObject d      DependencyPropertyChangedEventArgs e        var window   d as Window      if  window    null  amp  amp  window IsLoaded          window DialogResult   e NewValue as bool       After making this change any attachments to closed dialogs are ignored

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I would go this way   using GalaSoft MvvmLight  using GalaSoft MvvmLight Command      using GalaSoft MvvmLight Messaging       View  public partial class TestCloseWindow   Window       public TestCloseWindow             InitializeComponent            Messenger Default Register lt CloseWindowMsg gt  this   msg    gt  Close                 View Model  public class MainViewModel  ViewModelBase       ICommand  closeChildWindowCommand       public ICommand CloseChildWindowCommand           get               return  closeChildWindowCommand     closeChildWindowCommand   new RelayCommand      gt                    Messenger Default Send new CloseWindowMsg                                     public class CloseWindowMsg

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Assuming your login dialog is the first window that gets created  try this inside your LoginViewModel class       void OnLoginResponse bool loginSucceded                if  loginSucceded                        Window1 window   new Window1     DataContext   new MainWindowViewModel                  window Show                 App Current MainWindow Close                App Current MainWindow   window                    else                       LoginError   true

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This is probably very late  but I came across the same problem and I found a solution that works for me   I can t figure out how to create an app without dialogs maybe it s just a mind block   So I was at an impasse with MVVM and showing a dialog  So I came across this CodeProject article   http   www codeproject com KB WPF XAMLDialog aspx  Which is a UserControl that basically allows a window to be within the visual tree of another window not allowed in xaml   It also exposes a boolean DependencyProperty called IsShowing   You can set a style like typically in a resourcedictionary  that basically displays the dialog whenever the Content property of the control    null via triggers    lt Style TargetType   x Type d Dialog   gt       lt Style Triggers gt           lt Trigger Property  HasContent   Value  True  gt               lt Setter Property  Showing  Value  True    gt           lt  Trigger gt       lt  Style Triggers gt   lt  Style gt    In the view where you want to display the dialog simply have this    lt d Dialog Content   Binding Path DialogViewModel    gt    And in your ViewModel all you have to do is set the property to a value Note  the ViewModel class must support INotifyPropertyChanged for the view to know something happened     like so   DialogViewModel   new DisplayViewModel      To match the ViewModel with the View you should have something like this in a resourcedictionary    lt DataTemplate DataType   x Type vm DisplayViewModel   gt       lt vw DisplayView  gt   lt  DataTemplate gt    With all of that you get a one-liner code to show dialog  The problem you get is you can t really close the dialog with just the above code  So that s why you have to put in an event in a ViewModel base class which DisplayViewModel inherits from and instead of the code above  write this          var vm   new DisplayViewModel            vm RequestClose    new RequestCloseHandler DisplayViewModel RequestClose           DialogViewModel   vm    Then you can handle the result of the dialog via the callback   This may seem a little complex  but once the groundwork is laid  it s pretty straightforward  Again this is my implementation  I m sure there are others     Hope this helps  it saved me

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I would go this way   using GalaSoft MvvmLight  using GalaSoft MvvmLight Command      using GalaSoft MvvmLight Messaging       View  public partial class TestCloseWindow   Window       public TestCloseWindow             InitializeComponent            Messenger Default Register lt CloseWindowMsg gt  this   msg    gt  Close                 View Model  public class MainViewModel  ViewModelBase       ICommand  closeChildWindowCommand       public ICommand CloseChildWindowCommand           get               return  closeChildWindowCommand     closeChildWindowCommand   new RelayCommand      gt                    Messenger Default Send new CloseWindowMsg                                     public class CloseWindowMsg

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Where you need to close the window  simply put this in the viewmodel   ta-da    foreach  Window window in Application Current Windows                        if  window DataContext    this                                window Close                    return

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Here s what I initially did  which does work  however it seems rather long-winded and ugly  global static anything is never good   1  App xaml cs  public partial class App   Application          create a new global custom WPF Command     public static readonly RoutedUICommand LoggedIn   new RoutedUICommand        2  LoginForm xaml     bind the global command to a local eventhandler  lt CommandBinding Command  client App LoggedIn  Executed  OnLoggedIn    gt    3  LoginForm xaml cs     implement the local eventhandler in codebehind private void OnLoggedIn  object sender  ExecutedRoutedEventArgs e         DialogResult   true      Close        4  LoginFormViewModel cs     fire the global command from the viewmodel private void OnRemoteServerReturnedSuccess         App LoggedIn Execute this  null         I later on then removed all this code  and just had the LoginFormViewModel call the Close method on it s view  It ended up being much nicer and easier to follow  IMHO the point of patterns is to give people an easier way to understand what your app is doing  and in this case  MVVM was making it far harder to understand than if I hadn t used it  and was now an anti-pattern

User · Answer

Application Current MainWindow Close      Thats enough

User · Answer

Another solution is to create property with INotifyPropertyChanged in View Model like DialogResult  and then in Code Behind write this   public class SomeWindow  ChildWindow       private SomeViewModel  someViewModel       public SomeWindow                 InitializeComponent             this Loaded    SomeWindow Loaded          this Closed    SomeWindow Closed             void SomeWindow Loaded object sender  RoutedEventArgs e                 someViewModel   this DataContext as SomeViewModel           someViewModel PropertyChanged     someViewModel PropertyChanged             void SomeWindow Closed object sender  System EventArgs e                 someViewModel PropertyChanged -   someViewModel PropertyChanged          this Loaded -  SomeWindow Loaded          this Closed -  SomeWindow Closed             void  someViewModel PropertyChanged object sender  PropertyChangedEventArgs e                if  e PropertyName    SomeViewModel DialogResultPropertyName                        this DialogResult    someViewModel DialogResult                      The most important fragment is  someViewModel PropertyChanged  DialogResultPropertyName can be some public const string in SomeViewModel   I use this kind of trick to make some changes in View Controls in case when this is hard to do in ViewModel  OnPropertyChanged in ViewModel you can do anything you want in View  ViewModel is still  unit testable  and some small lines of code in code behind makes no difference

User · Answer

The way I would handle it is to add an event handler in my ViewModel  When the user was successfully logged in I would fire the event  In my View I would attach to this event and when it fired I would close the window

User · Answer

Application Current MainWindow Close      Thats enough

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Here is the simple bug free solution  with source code   It is working for me    Derive your ViewModel from INotifyPropertyChanged Create a observable property CloseDialog  in ViewModel  public void Execute            Do your task here         if task successful  assign true to CloseDialog     CloseDialog   true     private bool  closeDialog  public bool CloseDialog       get   return  closeDialog        set    closeDialog   value  OnPropertyChanged         public event PropertyChangedEventHandler PropertyChanged   private void OnPropertyChanged  CallerMemberName string property             if  PropertyChanged    null                PropertyChanged this  new PropertyChangedEventArgs property                   Attach a Handler in View for this property change       loginDialogViewModel   new LoginDialogViewModel        loginPanel DataContext    loginDialogViewModel       loginDialogViewModel PropertyChanged    OnPropertyChanged   Now you are almost done  In the event handler make DialogResult   true   protected void OnPropertyChanged object sender  PropertyChangedEventArgs args        if  args PropertyName     CloseDialog                 DialogResult   true

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There are a lot of comments arguing the pros and cons of MVVM here   For me  I agree with Nir  it s a matter of using the pattern appropriately and MVVM doesn t always fit   People seems to have become willing to sacrifice all of the most important principles of software design JUST to get it to fit MVVM   That said   i think your case could be a good fit with a bit of refactoring   In most cases I ve come across  WPF enables you to get by WITHOUT multiple Windows   Maybe you could try using Frames and Pages instead of Windows with DialogResults   In your case my suggestion would be have LoginFormViewModel handle the LoginCommand and if the login is invalid  set a property on LoginFormViewModel to an appropriate value  false or some enum value like UserAuthenticationStates FailedAuthentication    You d do the same for a successful login  true or some other enum value    You d then use a DataTrigger which responds to the various user authentication states and could use a simple Setter to change the Source property of the Frame     Having your login Window return a DialogResult i think is where you re getting confused  that DialogResult is really a property of your ViewModel   In my  admittedly limited experience with WPF  when something doesn t feel right it usually because I m thinking in terms of how i would ve done the same thing in WinForms    Hope that helps

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I ve read all the answers but I must say  most of them are just not good enough or even worse   You could handle this beatifully with DialogService class which responsibility is to show dialog window and return dialog result  I have create sample project demonstrating it s implementation and usage   here are most important parts     we will call this interface in our viewmodels public interface IDialogService       bool  ShowDialog object dialogViewModel  string caption        we need to display logindialog from mainwindow public class MainWindowViewModel   ViewModelBase       public string Message  get  set       public void ShowLoginCommandExecute                 var loginViewModel   new LoginViewModel            var dialogResult   this DialogService ShowDialog loginViewModel   Please  log in               after dialog is closed  do someting         if  dialogResult    true  amp  amp  loginViewModel IsLoginSuccessful                        this Message   string Format  Hello   0     loginViewModel Username                       public class DialogService   IDialogService       public bool  ShowDialog object dialogViewModel  string caption                var contentView   ViewLocator GetView dialogViewModel           var dlg   new DialogWindow                       Title   caption                    dlg PART ContentControl Content   contentView           return dlg ShowDialog              Isn t this just simpler  more straitforward  more readable and last but not least easier to debug than EventAggregator or other similar solutions   as you can see  In my view models I m  have used ViewModel first approach described in my post here  Best practice for calling View from ViewModel in WPF  Of course  in real world  the DialogService ShowDialog must have more option to configure the dialog  e g  buttons and commands they should execute  There are different way of doing so  but its out of scope

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I was inspired by Thejuan s answer to write a simpler attached property  No styles  no triggers  instead  you can just do this    lt Window             xmlns xc  clr-namespace ExCastle Wpf          xc DialogCloser DialogResult   Binding DialogResult   gt    This is almost as clean as if the WPF team had gotten it right and made DialogResult a dependency property in the first place  Just put a bool  DialogResult property on your ViewModel and implement INotifyPropertyChanged  and voil    your ViewModel can close the Window  and set its DialogResult  just by setting a property  MVVM as it should be   Here s the code for DialogCloser   using System Windows   namespace ExCastle Wpf       public static class DialogCloser               public static readonly DependencyProperty DialogResultProperty               DependencyProperty RegisterAttached                   DialogResult                   typeof bool                    typeof DialogCloser                   new PropertyMetadata DialogResultChanged             private static void DialogResultChanged              DependencyObject d              DependencyPropertyChangedEventArgs e                        var window   d as Window              if  window    null                  window DialogResult   e NewValue as bool                     public static void SetDialogResult Window target  bool  value                        target SetValue DialogResultProperty  value                       I ve also posted this on my blog

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You could have the ViewModel expose an event that the View registers to  Then  when the ViewModel decides its time to close the view  it fires that event which causes the view to close  If you want a specific result value passed back  then you would have a property in the ViewModel for that

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This is a simple and clean solution - You add an event to the ViewModel and instruct the Window to close itself when that event is fired   For more details see my blog post  Close window from ViewModel   XAML    lt Window   x Name  this    xmlns i  http   schemas microsoft com expression 2010 interactivity      xmlns ei  http   schemas microsoft com expression 2010 interactions  gt     lt i Interaction Triggers gt       lt i EventTrigger SourceObject   Binding   EventName  Closed  gt         lt ei CallMethodAction         TargetObject   Binding ElementName this           MethodName  Close   gt       lt  i EventTrigger gt     lt  i Interaction Triggers gt   lt Window gt    ViewModel   private ICommand  SaveAndCloseCommand  public ICommand SaveAndCloseCommand     get         return  SaveAndCloseCommand            SaveAndCloseCommand   new DelegateCommand SaveAndClose          private void SaveAndClose       Save      Close       public event EventHandler Closed  private void Close       if  Closed    null  Closed this  EventArgs Empty       Note  The example uses Prism s DelegateCommand  see Prism  Commanding   but any ICommand implementation can be used for that matter   You can use behaviors from this official package

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From my perspective the question is pretty good as the same approach would be used not only for the  Login  window  but for any kind of window  I ve reviewed a lot of suggestions and none are OK for me  Please review my suggestion that was taken from the MVVM design pattern article   Each ViewModel class should inherit from WorkspaceViewModel that has the RequestClose event and CloseCommand property of the ICommand type  The default implementation of the CloseCommand property will raise the RequestClose event   In order to get the window closed  the OnLoaded method of your window should be overridden   void CustomerWindow Loaded object sender  RoutedEventArgs e        CustomerViewModel customer   CustomerViewModel GetYourCustomer        DataContext   customer      customer RequestClose         gt    Close           or OnStartup method of you app       protected override void OnStartup StartupEventArgs e                base OnStartup e            MainWindow window   new MainWindow            var viewModel   new MainWindowViewModel            viewModel RequestClose    window Close          window DataContext   viewModel           window Show            I guess that RequestClose event and CloseCommand property implementation in the WorkspaceViewModel are pretty clear  but I will show them to be consistent   public abstract class WorkspaceViewModel   ViewModelBase    There s nothing interesting in ViewModelBase as it only implements the INotifyPropertyChanged interface       RelayCommand  closeCommand      public ICommand CloseCommand               get                       if   closeCommand    null                                 closeCommand   new RelayCommand                     param   gt  Close                       param   gt  CanClose                                                   return  closeCommand                       public event Action RequestClose       public virtual void Close                 if   RequestClose    null                         RequestClose                         public virtual bool CanClose                 return true            And the source code of the RelayCommand   public class RelayCommand   ICommand        region Constructors      public RelayCommand Action lt object gt  execute  Predicate lt object gt  canExecute                if  execute    null              throw new ArgumentNullException  execute              execute   execute           canExecute   canExecute             endregion    Constructors       region ICommand Members       DebuggerStepThrough      public bool CanExecute object parameter                return  canExecute    null   true    canExecute parameter              public event EventHandler CanExecuteChanged               add   CommandManager RequerySuggested    value            remove   CommandManager RequerySuggested -  value               public void Execute object parameter                 execute parameter               endregion    ICommand Members       region Fields      readonly Action lt object gt   execute      readonly Predicate lt object gt   canExecute        endregion    Fields       P S  Don t treat me badly for those sources  If I had them yesterday that would have saved me a few hours     P P S  Any comments or suggestions are welcome

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Just to add to the massive number of answers  I want to add the following  Assuming that you have a ICommand on your ViewModel  and you want that command to close its window  or any other action for that matter   you can use something like the following   var windows   Application Current Windows  for  var i 0 i lt  windows Count i         if  windows i  DataContext    this          windows i  Close      It s not perfect  and might be difficult to test  as it is hard to mock stub a static  but it is cleaner  IMHO  than the other solutions   Erick

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Why not just pass the window as a command parameter   C     private void Cancel  Window window            window Close           private ICommand  cancelCommand    public ICommand CancelCommand          get                return  cancelCommand       cancelCommand   new Command RelayCommand lt Window gt                                                           window     gt  Cancel  window                                                            window     gt    true                     XAML    lt Window x Class  WPFRunApp MainWindow          x Name   runWindow          lt Button Content  Cancel             Command   Binding Path CancelCommand              CommandParameter   Binding ElementName  runWindow     gt

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There are a lot of comments arguing the pros and cons of MVVM here   For me  I agree with Nir  it s a matter of using the pattern appropriately and MVVM doesn t always fit   People seems to have become willing to sacrifice all of the most important principles of software design JUST to get it to fit MVVM   That said   i think your case could be a good fit with a bit of refactoring   In most cases I ve come across  WPF enables you to get by WITHOUT multiple Windows   Maybe you could try using Frames and Pages instead of Windows with DialogResults   In your case my suggestion would be have LoginFormViewModel handle the LoginCommand and if the login is invalid  set a property on LoginFormViewModel to an appropriate value  false or some enum value like UserAuthenticationStates FailedAuthentication    You d do the same for a successful login  true or some other enum value    You d then use a DataTrigger which responds to the various user authentication states and could use a simple Setter to change the Source property of the Frame     Having your login Window return a DialogResult i think is where you re getting confused  that DialogResult is really a property of your ViewModel   In my  admittedly limited experience with WPF  when something doesn t feel right it usually because I m thinking in terms of how i would ve done the same thing in WinForms    Hope that helps

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Where you need to close the window  simply put this in the viewmodel   ta-da    foreach  Window window in Application Current Windows                        if  window DataContext    this                                window Close                    return

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public partial class MyWindow  Window       public ApplicationSelection               InitializeComponent           MyViewModel viewModel   new MyViewModel           DataContext   viewModel         viewModel RequestClose         gt    Close                 public class MyViewModel           Your code       public event Action RequestClose     public virtual void Close           if  RequestClose    null              RequestClose                 public void SomeFunction                 Do something         Close

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I was inspired by Thejuan s answer to write a simpler attached property  No styles  no triggers  instead  you can just do this    lt Window             xmlns xc  clr-namespace ExCastle Wpf          xc DialogCloser DialogResult   Binding DialogResult   gt    This is almost as clean as if the WPF team had gotten it right and made DialogResult a dependency property in the first place  Just put a bool  DialogResult property on your ViewModel and implement INotifyPropertyChanged  and voil    your ViewModel can close the Window  and set its DialogResult  just by setting a property  MVVM as it should be   Here s the code for DialogCloser   using System Windows   namespace ExCastle Wpf       public static class DialogCloser               public static readonly DependencyProperty DialogResultProperty               DependencyProperty RegisterAttached                   DialogResult                   typeof bool                    typeof DialogCloser                   new PropertyMetadata DialogResultChanged             private static void DialogResultChanged              DependencyObject d              DependencyPropertyChangedEventArgs e                        var window   d as Window              if  window    null                  window DialogResult   e NewValue as bool                     public static void SetDialogResult Window target  bool  value                        target SetValue DialogResultProperty  value                       I ve also posted this on my blog

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While this doesn t answer the question of how to do this via the viewmodel  this does show how to do it using only XAML   the blend SDK   I chose to download and use two files from the Blend SDK  both of which you can as a package from Microsoft through NuGet  The files are   System Windows Interactivity dll and Microsoft Expression Interactions dll  Microsoft Expression Interactions dll gives you nice capabilities such as the ability to set property or invoke a method on your viewmodel or other target and has other widgets inside as well   Some XAML    lt Window x Class  Blah Blah MyWindow              xmlns i  http   schemas microsoft com expression 2010 interactivity      xmlns ei  http   schemas microsoft com expression 2010 interactions        gt    lt StackPanel gt       lt Button x Name  OKButton  Content  OK  gt          lt i Interaction Triggers gt             lt i EventTrigger EventName  Click  gt                lt ei ChangePropertyAction                       TargetObject   Binding RelativeSource  RelativeSource FindAncestor  AncestorType  x Type Window                           PropertyName  DialogResult                        Value  True                        IsEnabled   Binding SomeBoolOnTheVM     gt                                             lt  i EventTrigger gt       lt  Button gt       lt Button x Name  CancelButton  Content  Cancel  gt          lt i Interaction Triggers gt             lt i EventTrigger EventName  Click  gt                lt ei ChangePropertyAction                       TargetObject   Binding RelativeSource  RelativeSource FindAncestor  AncestorType  x Type Window                           PropertyName  DialogResult                        Value  False    gt                                             lt  i EventTrigger gt       lt  Button gt        lt Button x Name  CloseButton  Content  Close  gt          lt i Interaction Triggers gt                   lt i EventTrigger EventName  Click  gt                       lt  -- method being invoked should be void w  no args -- gt                       lt ei CallMethodAction                         TargetObject   Binding RelativeSource  RelativeSource FindAncestor  AncestorType  x Type Window                             MethodName  Close    gt                   lt  i EventTrigger gt               lt  i Interaction Triggers gt       lt  Button gt    lt StackPanel gt   lt  Window gt    Note that if you re just going for simple OK Cancel behavior  you can get away w  using the IsDefault and IsCancel properties as long as the window is shown w  Window ShowDialog    I personally had problems w  a button that had the IsDefault property set to true  but it was hidden when the page is loaded  It didn t seem to want to play nicely after it was shown  so I just am setting the Window DialogResult property as shown above instead and it works for me

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I used attached behaviours to close the window  Bind a  signal  property on your ViewModel to the attached behaviour  I actually use a trigger  When it s set to true  the behaviour closes the window   http   adammills wordpress com 2009 07 01 window-close-from-xaml

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Just to add to the massive number of answers  I want to add the following  Assuming that you have a ICommand on your ViewModel  and you want that command to close its window  or any other action for that matter   you can use something like the following   var windows   Application Current Windows  for  var i 0 i lt  windows Count i         if  windows i  DataContext    this          windows i  Close      It s not perfect  and might be difficult to test  as it is hard to mock stub a static  but it is cleaner  IMHO  than the other solutions   Erick

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You could have the ViewModel expose an event that the View registers to  Then  when the ViewModel decides its time to close the view  it fires that event which causes the view to close  If you want a specific result value passed back  then you would have a property in the ViewModel for that

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Create a Dependency Property in your View any UserControl or Window you want to close   Like below    public bool CloseTrigger                       get   return  bool GetValue CloseTriggerProperty                 set   SetValue CloseTriggerProperty  value                        public static readonly DependencyProperty CloseTriggerProperty               DependencyProperty Register  CloseTrigger   typeof bool   typeof ControlEventBase   new PropertyMetadata new PropertyChangedCallback OnCloseTriggerChanged              private static void OnCloseTriggerChanged DependencyObject dp  DependencyPropertyChangedEventArgs e                          write Window Exit Code             And bind it from your ViewModel s property    lt Window x Class  WpfStackOverflowTempProject MainWindow          xmlns  http   schemas microsoft com winfx 2006 xaml presentation          xmlns x  http   schemas microsoft com winfx 2006 xaml          Title  MainWindow   Width  525          CloseTrigger   Binding Path CloseWindow Mode TwoWay     Property In VeiwModel   private bool closeWindow       public bool CloseWindow               get   return closeWindow            set                         closeWindow   value              RaiseChane  CloseWindow                      Now trigger the close operation by changing the CloseWindow value in ViewModel

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Assuming your login dialog is the first window that gets created  try this inside your LoginViewModel class       void OnLoginResponse bool loginSucceded                if  loginSucceded                        Window1 window   new Window1     DataContext   new MainWindowViewModel                  window Show                 App Current MainWindow Close                App Current MainWindow   window                    else                       LoginError   true

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From my perspective the question is pretty good as the same approach would be used not only for the  Login  window  but for any kind of window  I ve reviewed a lot of suggestions and none are OK for me  Please review my suggestion that was taken from the MVVM design pattern article   Each ViewModel class should inherit from WorkspaceViewModel that has the RequestClose event and CloseCommand property of the ICommand type  The default implementation of the CloseCommand property will raise the RequestClose event   In order to get the window closed  the OnLoaded method of your window should be overridden   void CustomerWindow Loaded object sender  RoutedEventArgs e        CustomerViewModel customer   CustomerViewModel GetYourCustomer        DataContext   customer      customer RequestClose         gt    Close           or OnStartup method of you app       protected override void OnStartup StartupEventArgs e                base OnStartup e            MainWindow window   new MainWindow            var viewModel   new MainWindowViewModel            viewModel RequestClose    window Close          window DataContext   viewModel           window Show            I guess that RequestClose event and CloseCommand property implementation in the WorkspaceViewModel are pretty clear  but I will show them to be consistent   public abstract class WorkspaceViewModel   ViewModelBase    There s nothing interesting in ViewModelBase as it only implements the INotifyPropertyChanged interface       RelayCommand  closeCommand      public ICommand CloseCommand               get                       if   closeCommand    null                                 closeCommand   new RelayCommand                     param   gt  Close                       param   gt  CanClose                                                   return  closeCommand                       public event Action RequestClose       public virtual void Close                 if   RequestClose    null                         RequestClose                         public virtual bool CanClose                 return true            And the source code of the RelayCommand   public class RelayCommand   ICommand        region Constructors      public RelayCommand Action lt object gt  execute  Predicate lt object gt  canExecute                if  execute    null              throw new ArgumentNullException  execute              execute   execute           canExecute   canExecute             endregion    Constructors       region ICommand Members       DebuggerStepThrough      public bool CanExecute object parameter                return  canExecute    null   true    canExecute parameter              public event EventHandler CanExecuteChanged               add   CommandManager RequerySuggested    value            remove   CommandManager RequerySuggested -  value               public void Execute object parameter                 execute parameter               endregion    ICommand Members       region Fields      readonly Action lt object gt   execute      readonly Predicate lt object gt   canExecute        endregion    Fields       P S  Don t treat me badly for those sources  If I had them yesterday that would have saved me a few hours     P P S  Any comments or suggestions are welcome

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This is probably very late  but I came across the same problem and I found a solution that works for me   I can t figure out how to create an app without dialogs maybe it s just a mind block   So I was at an impasse with MVVM and showing a dialog  So I came across this CodeProject article   http   www codeproject com KB WPF XAMLDialog aspx  Which is a UserControl that basically allows a window to be within the visual tree of another window not allowed in xaml   It also exposes a boolean DependencyProperty called IsShowing   You can set a style like typically in a resourcedictionary  that basically displays the dialog whenever the Content property of the control    null via triggers    lt Style TargetType   x Type d Dialog   gt       lt Style Triggers gt           lt Trigger Property  HasContent   Value  True  gt               lt Setter Property  Showing  Value  True    gt           lt  Trigger gt       lt  Style Triggers gt   lt  Style gt    In the view where you want to display the dialog simply have this    lt d Dialog Content   Binding Path DialogViewModel    gt    And in your ViewModel all you have to do is set the property to a value Note  the ViewModel class must support INotifyPropertyChanged for the view to know something happened     like so   DialogViewModel   new DisplayViewModel      To match the ViewModel with the View you should have something like this in a resourcedictionary    lt DataTemplate DataType   x Type vm DisplayViewModel   gt       lt vw DisplayView  gt   lt  DataTemplate gt    With all of that you get a one-liner code to show dialog  The problem you get is you can t really close the dialog with just the above code  So that s why you have to put in an event in a ViewModel base class which DisplayViewModel inherits from and instead of the code above  write this          var vm   new DisplayViewModel            vm RequestClose    new RequestCloseHandler DisplayViewModel RequestClose           DialogViewModel   vm    Then you can handle the result of the dialog via the callback   This may seem a little complex  but once the groundwork is laid  it s pretty straightforward  Again this is my implementation  I m sure there are others     Hope this helps  it saved me

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I ended up blending Joe White s answer and some code from Adam Mills s answer  since I needed to show a user control in a programmatically created window  So the DialogCloser need not be on the window  it can be on the user control itself   lt UserControl         xmlns xw  clr-namespace Wpf      xw DialogCloser DialogResult   Binding DialogResult   gt    And the DialogCloser will find the window of the user control if it was not attached to the window itself   namespace Wpf     public static class DialogCloser         public static readonly DependencyProperty DialogResultProperty           DependencyProperty RegisterAttached               DialogResult               typeof bool                typeof DialogCloser               new PropertyMetadata DialogResultChanged         private static void DialogResultChanged          DependencyObject d          DependencyPropertyChangedEventArgs e              var window   d GetWindow          if  window    null          window DialogResult   e NewValue as bool              public static void SetDialogResult DependencyObject target  bool  value              target SetValue DialogResultProperty  value                public static class Extensions         public static Window GetWindow this DependencyObject sender               Window window   sender  as Window                return window    Window GetWindow  sender

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I ended up blending Joe White s answer and some code from Adam Mills s answer  since I needed to show a user control in a programmatically created window  So the DialogCloser need not be on the window  it can be on the user control itself   lt UserControl         xmlns xw  clr-namespace Wpf      xw DialogCloser DialogResult   Binding DialogResult   gt    And the DialogCloser will find the window of the user control if it was not attached to the window itself   namespace Wpf     public static class DialogCloser         public static readonly DependencyProperty DialogResultProperty           DependencyProperty RegisterAttached               DialogResult               typeof bool                typeof DialogCloser               new PropertyMetadata DialogResultChanged         private static void DialogResultChanged          DependencyObject d          DependencyPropertyChangedEventArgs e              var window   d GetWindow          if  window    null          window DialogResult   e NewValue as bool              public static void SetDialogResult DependencyObject target  bool  value              target SetValue DialogResultProperty  value                public static class Extensions         public static Window GetWindow this DependencyObject sender               Window window   sender  as Window                return window    Window GetWindow  sender

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Why not just pass the window as a command parameter   C     private void Cancel  Window window            window Close           private ICommand  cancelCommand    public ICommand CancelCommand          get                return  cancelCommand       cancelCommand   new Command RelayCommand lt Window gt                                                           window     gt  Cancel  window                                                            window     gt    true                     XAML    lt Window x Class  WPFRunApp MainWindow          x Name   runWindow          lt Button Content  Cancel             Command   Binding Path CancelCommand              CommandParameter   Binding ElementName  runWindow     gt

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Behavior is the most convenient way here     From one hand  it can be binded to the given viewmodel  that can signal  close the form    From another hand  it has access to the form itself so can subscribe to necessary form-specific events  or show confirmation dialog  or anything else    Writing necessary behavior can be seen boring very first time  However  from now on  you can reuse it on every single form you need by exact one-liner XAML snippet  And if necessary  you can extract it as a separate assembly so it can be included into any next project you want

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I used attached behaviours to close the window  Bind a  signal  property on your ViewModel to the attached behaviour  I actually use a trigger  When it s set to true  the behaviour closes the window   http   adammills wordpress com 2009 07 01 window-close-from-xaml

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This is a simple and clean solution - You add an event to the ViewModel and instruct the Window to close itself when that event is fired   For more details see my blog post  Close window from ViewModel   XAML    lt Window   x Name  this    xmlns i  http   schemas microsoft com expression 2010 interactivity      xmlns ei  http   schemas microsoft com expression 2010 interactions  gt     lt i Interaction Triggers gt       lt i EventTrigger SourceObject   Binding   EventName  Closed  gt         lt ei CallMethodAction         TargetObject   Binding ElementName this           MethodName  Close   gt       lt  i EventTrigger gt     lt  i Interaction Triggers gt   lt Window gt    ViewModel   private ICommand  SaveAndCloseCommand  public ICommand SaveAndCloseCommand     get         return  SaveAndCloseCommand            SaveAndCloseCommand   new DelegateCommand SaveAndClose          private void SaveAndClose       Save      Close       public event EventHandler Closed  private void Close       if  Closed    null  Closed this  EventArgs Empty       Note  The example uses Prism s DelegateCommand  see Prism  Commanding   but any ICommand implementation can be used for that matter   You can use behaviors from this official package

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While this doesn t answer the question of how to do this via the viewmodel  this does show how to do it using only XAML   the blend SDK   I chose to download and use two files from the Blend SDK  both of which you can as a package from Microsoft through NuGet  The files are   System Windows Interactivity dll and Microsoft Expression Interactions dll  Microsoft Expression Interactions dll gives you nice capabilities such as the ability to set property or invoke a method on your viewmodel or other target and has other widgets inside as well   Some XAML    lt Window x Class  Blah Blah MyWindow              xmlns i  http   schemas microsoft com expression 2010 interactivity      xmlns ei  http   schemas microsoft com expression 2010 interactions        gt    lt StackPanel gt       lt Button x Name  OKButton  Content  OK  gt          lt i Interaction Triggers gt             lt i EventTrigger EventName  Click  gt                lt ei ChangePropertyAction                       TargetObject   Binding RelativeSource  RelativeSource FindAncestor  AncestorType  x Type Window                           PropertyName  DialogResult                        Value  True                        IsEnabled   Binding SomeBoolOnTheVM     gt                                             lt  i EventTrigger gt       lt  Button gt       lt Button x Name  CancelButton  Content  Cancel  gt          lt i Interaction Triggers gt             lt i EventTrigger EventName  Click  gt                lt ei ChangePropertyAction                       TargetObject   Binding RelativeSource  RelativeSource FindAncestor  AncestorType  x Type Window                           PropertyName  DialogResult                        Value  False    gt                                             lt  i EventTrigger gt       lt  Button gt        lt Button x Name  CloseButton  Content  Close  gt          lt i Interaction Triggers gt                   lt i EventTrigger EventName  Click  gt                       lt  -- method being invoked should be void w  no args -- gt                       lt ei CallMethodAction                         TargetObject   Binding RelativeSource  RelativeSource FindAncestor  AncestorType  x Type Window                             MethodName  Close    gt                   lt  i EventTrigger gt               lt  i Interaction Triggers gt       lt  Button gt    lt StackPanel gt   lt  Window gt    Note that if you re just going for simple OK Cancel behavior  you can get away w  using the IsDefault and IsCancel properties as long as the window is shown w  Window ShowDialog    I personally had problems w  a button that had the IsDefault property set to true  but it was hidden when the page is loaded  It didn t seem to want to play nicely after it was shown  so I just am setting the Window DialogResult property as shown above instead and it works for me

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Another solution is to create property with INotifyPropertyChanged in View Model like DialogResult  and then in Code Behind write this   public class SomeWindow  ChildWindow       private SomeViewModel  someViewModel       public SomeWindow                 InitializeComponent             this Loaded    SomeWindow Loaded          this Closed    SomeWindow Closed             void SomeWindow Loaded object sender  RoutedEventArgs e                 someViewModel   this DataContext as SomeViewModel           someViewModel PropertyChanged     someViewModel PropertyChanged             void SomeWindow Closed object sender  System EventArgs e                 someViewModel PropertyChanged -   someViewModel PropertyChanged          this Loaded -  SomeWindow Loaded          this Closed -  SomeWindow Closed             void  someViewModel PropertyChanged object sender  PropertyChangedEventArgs e                if  e PropertyName    SomeViewModel DialogResultPropertyName                        this DialogResult    someViewModel DialogResult                      The most important fragment is  someViewModel PropertyChanged  DialogResultPropertyName can be some public const string in SomeViewModel   I use this kind of trick to make some changes in View Controls in case when this is hard to do in ViewModel  OnPropertyChanged in ViewModel you can do anything you want in View  ViewModel is still  unit testable  and some small lines of code in code behind makes no difference

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I ve read all the answers but I must say  most of them are just not good enough or even worse   You could handle this beatifully with DialogService class which responsibility is to show dialog window and return dialog result  I have create sample project demonstrating it s implementation and usage   here are most important parts     we will call this interface in our viewmodels public interface IDialogService       bool  ShowDialog object dialogViewModel  string caption        we need to display logindialog from mainwindow public class MainWindowViewModel   ViewModelBase       public string Message  get  set       public void ShowLoginCommandExecute                 var loginViewModel   new LoginViewModel            var dialogResult   this DialogService ShowDialog loginViewModel   Please  log in               after dialog is closed  do someting         if  dialogResult    true  amp  amp  loginViewModel IsLoginSuccessful                        this Message   string Format  Hello   0     loginViewModel Username                       public class DialogService   IDialogService       public bool  ShowDialog object dialogViewModel  string caption                var contentView   ViewLocator GetView dialogViewModel           var dlg   new DialogWindow                       Title   caption                    dlg PART ContentControl Content   contentView           return dlg ShowDialog              Isn t this just simpler  more straitforward  more readable and last but not least easier to debug than EventAggregator or other similar solutions   as you can see  In my view models I m  have used ViewModel first approach described in my post here  Best practice for calling View from ViewModel in WPF  Of course  in real world  the DialogService ShowDialog must have more option to configure the dialog  e g  buttons and commands they should execute  There are different way of doing so  but its out of scope

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Here s what I initially did  which does work  however it seems rather long-winded and ugly  global static anything is never good   1  App xaml cs  public partial class App   Application          create a new global custom WPF Command     public static readonly RoutedUICommand LoggedIn   new RoutedUICommand        2  LoginForm xaml     bind the global command to a local eventhandler  lt CommandBinding Command  client App LoggedIn  Executed  OnLoggedIn    gt    3  LoginForm xaml cs     implement the local eventhandler in codebehind private void OnLoggedIn  object sender  ExecutedRoutedEventArgs e         DialogResult   true      Close        4  LoginFormViewModel cs     fire the global command from the viewmodel private void OnRemoteServerReturnedSuccess         App LoggedIn Execute this  null         I later on then removed all this code  and just had the LoginFormViewModel call the Close method on it s view  It ended up being much nicer and easier to follow  IMHO the point of patterns is to give people an easier way to understand what your app is doing  and in this case  MVVM was making it far harder to understand than if I hadn t used it  and was now an anti-pattern

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Here s what I initially did  which does work  however it seems rather long-winded and ugly  global static anything is never good   1  App xaml cs  public partial class App   Application          create a new global custom WPF Command     public static readonly RoutedUICommand LoggedIn   new RoutedUICommand        2  LoginForm xaml     bind the global command to a local eventhandler  lt CommandBinding Command  client App LoggedIn  Executed  OnLoggedIn    gt    3  LoginForm xaml cs     implement the local eventhandler in codebehind private void OnLoggedIn  object sender  ExecutedRoutedEventArgs e         DialogResult   true      Close        4  LoginFormViewModel cs     fire the global command from the viewmodel private void OnRemoteServerReturnedSuccess         App LoggedIn Execute this  null         I later on then removed all this code  and just had the LoginFormViewModel call the Close method on it s view  It ended up being much nicer and easier to follow  IMHO the point of patterns is to give people an easier way to understand what your app is doing  and in this case  MVVM was making it far harder to understand than if I hadn t used it  and was now an anti-pattern

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public partial class MyWindow  Window       public ApplicationSelection               InitializeComponent           MyViewModel viewModel   new MyViewModel           DataContext   viewModel         viewModel RequestClose         gt    Close                 public class MyViewModel           Your code       public event Action RequestClose     public virtual void Close           if  RequestClose    null              RequestClose                 public void SomeFunction                 Do something         Close

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Behavior is the most convenient way here     From one hand  it can be binded to the given viewmodel  that can signal  close the form    From another hand  it has access to the form itself so can subscribe to necessary form-specific events  or show confirmation dialog  or anything else    Writing necessary behavior can be seen boring very first time  However  from now on  you can reuse it on every single form you need by exact one-liner XAML snippet  And if necessary  you can extract it as a separate assembly so it can be included into any next project you want

[c#] How should the ViewModel close the form?

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