Handling the window closing event with WPF MVVM Light Toolkit

Question

I d like to handle the Closing event  when a user clicks the upper right  X  button  of my window in order to eventually display a confirm message or and cancel the closing   I know how to do this in the code-behind  subscribe to the Closing event of the window then use the CancelEventArgs Cancel property   But I m using MVVM so I m not sure it s the good approach   I think the good approach would be to bind the Closing event to a Command in my ViewModel   I tried that    lt i Interaction Triggers gt       lt i EventTrigger EventName  Closing  gt           lt cmd EventToCommand Command   Binding CloseCommand     gt       lt  i EventTrigger gt   lt  i Interaction Triggers gt    With an associated RelayCommand in my ViewModel but it doesn t work  the command s code is not executed

User · Answer

This code works just fine   ViewModel cs   public ICommand WindowClosing       get               return new RelayCommand lt CancelEventArgs gt                args    gt                                      and in XAML    lt i Interaction Triggers gt       lt i EventTrigger EventName  Closing  gt           lt command EventToCommand Command   Binding WindowClosing   PassEventArgsToCommand  True    gt       lt  i EventTrigger gt   lt  i Interaction Triggers gt    assuming that    ViewModel is assigned to a DataContext of the main container  xmlns command  clr-namespace GalaSoft MvvmLight Command assembly GalaSoft MvvmLight Extras SL5  xmlns i  clr-namespace System Windows Interactivity assembly System Windows Interactivity

User · Answer

Basically  window event may not be assigned to MVVM  In general  the Close button show a Dialog box to ask the user  save   yes no cancel   and this may not be achieved by the MVVM   You may keep the OnClosing event handler  where you call the Model Close CanExecute   and set the boolean result in the event property  So after the CanExecute   call if true  OR in the OnClosed event  call the Model Close Execute

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I would simply associate the handler in the View constructor  MyWindow             Set up ViewModel  assign to DataContext etc      Closing    viewModel OnWindowClosing     Then add the handler to the ViewModel  using System ComponentModel   public void OnWindowClosing object sender  CancelEventArgs e           Handle closing logic  set e Cancel as needed    In this case  you gain exactly nothing except complexity by using a more elaborate pattern with more indirection  5 extra lines of XAML plus Command pattern   The  quot zero code-behind quot  mantra is not the goal in itself  the point is to decouple ViewModel from the View  Even when the event is bound in code-behind of the View  the ViewModel does not depend on the View and the closing logic can be unit-tested

User · Answer

I would be tempted to use an event handler within your App xaml cs file that will allow you to decide on whether to close the application or not   For example you could then have something like the following code in your App xaml cs file   protected override void OnStartup StartupEventArgs e        base OnStartup e          Create the ViewModel to attach the window to     MainWindow window   new MainWindow        var viewModel   new MainWindowViewModel            Create the handler that will allow the window to close when the viewModel asks      EventHandler handler   null      handler   delegate                    Code here to decide on closing the application                  returns resultClose which is true if we want to close            if resultClose    true                        viewModel RequestClose -  handler              window Close                        viewModel RequestClose    handler       window DataContaxt   viewModel       window Show         Then within your MainWindowViewModel code you could have the following    region Fields RelayCommand closeCommand   endregion   region CloseCommand      lt summary gt      Returns the command that  when invoked  attempts     to remove this workspace from the user interface       lt  summary gt  public ICommand CloseCommand       get               if  closeCommand    null              closeCommand   new RelayCommand param   gt  this OnRequestClose              return closeCommand           endregion    CloseCommand   region RequestClose  event        lt summary gt      Raised when this workspace should be removed from the UI       lt  summary gt  public event EventHandler RequestClose        lt summary gt      If requested to close and a RequestClose delegate has been set then call it       lt  summary gt  void OnRequestClose         EventHandler handler   this RequestClose      if  handler    null                handler this  EventArgs Empty             endregion    RequestClose  event

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I haven t done much testing with this but it seems to work  Here s what I came up with   namespace OrtzIRC WPF       using System      using System Windows      using OrtzIRC WPF ViewModels            lt summary gt          Interaction logic for App xaml          lt  summary gt      public partial class App   Application               private MainViewModel viewModel   new MainViewModel            private MainWindow window   new MainWindow             protected override void OnStartup StartupEventArgs e                        base OnStartup e                viewModel RequestClose    ViewModelRequestClose               window DataContext   viewModel              window Closing    Window Closing              window Show                       private void ViewModelRequestClose object sender  EventArgs e                        viewModel RequestClose -  ViewModelRequestClose              window Close                       private void Window Closing object sender  System ComponentModel CancelEventArgs e                        window Closing -  Window Closing              viewModel RequestClose -  ViewModelRequestClose    Otherwise Close gets called again             viewModel CloseCommand Execute null

User · Answer

This option is even easier  and maybe is suitable for you  In your View Model constructor  you can subscribe the Main Window closing event like this   Application Current MainWindow Closing    new CancelEventHandler MainWindow Closing    void MainWindow Closing object sender  CancelEventArgs e                  Your code to handle the event     All the best

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We use AttachedCommandBehavior for this  You can attach any event to a command on your view model avoiding any code behind   We use it throughout our solution and have almost zero code behind  http   marlongrech wordpress com 2008 12 13 attachedcommandbehavior-v2-aka-acb

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The asker should use STAS answer  but for readers who use prism and no galasoft mvvmlight  they may want to try what I used   In the definition at the top for window or usercontrol  etc define namespace   xmlns i  clr-namespace System Windows Interactivity assembly System Windows Interactivity    And just below that definition    lt i Interaction Triggers gt           lt i EventTrigger EventName  Closing  gt               lt i InvokeCommandAction Command   Binding WindowClosing   CommandParameter   Binding     gt           lt  i EventTrigger gt   lt  i Interaction Triggers gt    Property in your viewmodel   public ICommand WindowClosing   get  private set      Attach delegatecommand in your viewmodel constructor   this WindowClosing   new DelegateCommand lt object gt  this OnWindowClosing     Finally  your code you want to reach on close of the control window whatever   private void OnWindowClosing object obj                          put code here

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Using MVVM Light Toolkit   Assuming that there is an Exit command in view model   ICommand  exitCommand  public ICommand ExitCommand       get               if   exitCommand    null               exitCommand   new RelayCommand lt object gt  call   gt  OnExit             return  exitCommand           void OnExit          var msg   new NotificationMessageAction lt object gt  this   ExitApplication    o    gt           Messenger Default Send msg       This is received in the view   Messenger Default Register lt NotificationMessageAction lt object gt  gt  this   m    gt  if  m Notification     ExitApplication          Application Current Shutdown          On the other hand  I handle Closing event in MainWindow  using the instance of ViewModel   private void Window Closing object sender  System ComponentModel CancelEventArgs e         if    ViewModel MainViewModel DataContext  CancelBeforeClose            e Cancel   true      CancelBeforeClose checks the current state of view model and returns true if closing should be stopped    Hope it helps someone

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Geez  seems like a lot of code going on here for this  Stas above had the right approach for minimal effort   Here is my adaptation  using MVVMLight but should be recognizable     Oh and the PassEventArgsToCommand  True  is definitely needed as indicated above    credit to Laurent Bugnion http   blog galasoft ch archive 2009 10 18 clean-shutdown-in-silverlight-and-wpf-applications aspx          MainWindow Xaml           WindowStyle  ThreeDBorderWindow       WindowStartupLocation  Manual  gt      lt i Interaction Triggers gt       lt i EventTrigger EventName  Closing  gt           lt cmd EventToCommand Command   Binding WindowClosingCommand   PassEventArgsToCommand  True    gt       lt  i EventTrigger gt   lt  i Interaction Triggers gt     In the view model       lt summary gt       public RelayCommand lt CancelEventArgs gt  WindowClosingCommand     lt  summary gt  public RelayCommand lt CancelEventArgs gt  WindowClosingCommand   get  private set                              Window Closing         WindowClosingCommand   new RelayCommand lt CancelEventArgs gt   args    gt                                                                                                                                                    ShutdownService MainWindowClosing args                                                                                                                                                   args    gt  CanShutdown     in the ShutdownService            lt summary gt            ask the application to shutdown          lt  summary gt      public static void MainWindowClosing CancelEventArgs e                e Cancel   true       CANCEL THE CLOSE - let the shutdown service decide what to do with the shutdown request         RequestShutdown            RequestShutdown looks something like the following but basicallyRequestShutdown or whatever it is named decides whether to shutdown the application or not  which will merrily close the window anyway                         lt summary gt            ask the application to shutdown          lt  summary gt      public static void RequestShutdown                     Unless one of the listeners aborted the shutdown  we proceed   If they abort the shutdown  they are responsible for restarting it too           var shouldAbortShutdown   false          Logger InfoFormat  Application starting shutdown at  0       DateTime Now           var msg   new NotificationMessageAction lt bool gt               Notifications ConfirmShutdown              shouldAbort   gt  shouldAbortShutdown    shouldAbort               recipients should answer either true or false with msg execute true  etc           Messenger Default Send msg  Notifications ConfirmShutdown            if   shouldAbortShutdown                           This time it is for real             Messenger Default Send new NotificationMessage Notifications NotifyShutdown                                      Notifications NotifyShutdown               Logger InfoFormat  Application has shutdown at  0    DateTime Now               Application Current Shutdown                      else             Logger InfoFormat  Application shutdown aborted at  0    DateTime Now

User · Answer

private void Window Closing object sender  System ComponentModel CancelEventArgs e                MessageBox Show  closing

User · Answer

Here is an answer according to the MVVM-pattern if you don t want to know about the Window  or any of its event  in the ViewModel   public interface IClosing            lt summary gt          Executes when window is closing          lt  summary gt           lt returns gt Whether the windows should be closed by the caller lt  returns gt      bool OnClosing        In the ViewModel add the interface and implementation  public bool OnClosing         bool close   true         Ask whether to save changes och cancel etc       close   false    If you want to cancel close      return close      In the Window I add the Closing event  This code behind doesn t break the MVVM pattern  The View can know about the viewmodel   void Window Closing object sender  System ComponentModel CancelEventArgs e        IClosing context   DataContext as IClosing      if  context    null                e Cancel    context OnClosing

[c#] Handling the window closing event with WPF / MVVM Light Toolkit

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