MVVM Passing EventArgs As Command Parameter

Question

I m using Microsoft Expression Blend 4 I have a Browser          XAML   ConnectionView   Empty Code Behind             lt WebBrowser local AttachedProperties BrowserSource   Binding Source   gt               lt i Interaction Triggers gt                   lt i EventTrigger gt                       lt i InvokeCommandAction Command   Binding LoadedEvent    gt                   lt  i EventTrigger gt                   lt i EventTrigger EventName  Navigated  gt                       lt i InvokeCommandAction Command   Binding NavigatedEvent   CommandParameter           gt                   lt  i EventTrigger gt               lt  i Interaction Triggers gt           lt  WebBrowser gt        C    AttachedProperties class    public static class AttachedProperties               public static readonly DependencyProperty BrowserSourceProperty   DependencyProperty   RegisterAttached    BrowserSource    typeof   string     typeof   AttachedProperties     new UIPropertyMetadata   null   BrowserSourcePropertyChanged               public static string GetBrowserSource   DependencyObject  DependencyObject                         return   string    DependencyObject   GetValue   BrowserSourceProperty                       public static void SetBrowserSource   DependencyObject  DependencyObject   string Value                          DependencyObject   SetValue   BrowserSourceProperty   Value                       public static void BrowserSourcePropertyChanged   DependencyObject  DependencyObject   DependencyPropertyChangedEventArgs  DependencyPropertyChangedEventArgs                         WebBrowser  WebBrowser    DependencyObject as WebBrowser              if    WebBrowser    null                                 string URL    DependencyPropertyChangedEventArgs   NewValue as string                   WebBrowser   Source   URL    null   new Uri   URL     null                                    C    ConnectionViewModel Class   public class ConnectionViewModel   ViewModelBase                   public string Source                               get   return Get lt string gt     Source                       set   Set    Source    value                                 public void Execute ExitCommand                                   Application   Current   Shutdown                                 public void Execute LoadedEvent                                   MessageBox   Show       Execute LoadedEvent                        Source                                       public void Execute NavigatedEvent                                   MessageBox   Show       Execute NavigatedEvent                                C    ViewModelBase class  Here  Finally   Binding with commands works well and MessageBoxes shown     My Question   How to pass NavigationEventArgs as Command Parameters when Navigated Event occurs

User · Answer

Prism s InvokeCommandAction will pass the event args by default if CommandParameter is not set   https   docs microsoft com en-us previous-versions msp-n-p gg405494 v pandp 40  passing-eventargs-parameters-to-the-command  Here is an example  Note the use of prism InvokeCommandAction instead of i InvokeCommandAction    lt i Interaction Triggers gt       lt i EventTrigger EventName  Sorting  gt           lt prism InvokeCommandAction Command   Binding SortingCommand    gt       lt  i EventTrigger gt   lt  i Interaction Triggers gt    The ViewModel      private DelegateCommand lt EventArgs gt   sortingCommand       public DelegateCommand lt EventArgs gt  SortingCommand   gt   sortingCommand      sortingCommand   new DelegateCommand lt EventArgs gt  OnSortingCommand         private void OnSortingCommand EventArgs obj                  do stuff         There is a new version of the Prismlibrary documentation

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I know this is a fairly old question  but I ran into the same problem today and wasn t too interested in referencing all of MVVMLight just so I can use event triggers with event args  I have used MVVMLight in the past and it s a great framework  but I just don t want to use it for my projects any more   What I did to resolve this problem was create an ULTRA minimal  EXTREMELY adaptable custom trigger action that would allow me to bind to the command and provide an event args converter to pass on the args to the command s CanExecute and Execute functions  You don t want to pass the event args verbatim  as that would result in view layer types being sent to the view model layer  which should never happen in MVVM    Here is the EventCommandExecuter class I came up with   public class EventCommandExecuter   TriggerAction lt DependencyObject gt         region Constructors      public EventCommandExecuter             this CultureInfo CurrentCulture                   public EventCommandExecuter CultureInfo culture                Culture   culture              endregion       region Properties       region Command      public ICommand Command               get   return  ICommand GetValue CommandProperty             set   SetValue CommandProperty  value                public static readonly DependencyProperty CommandProperty           DependencyProperty Register  Command   typeof ICommand   typeof EventCommandExecuter   new PropertyMetadata null          endregion       region EventArgsConverterParameter      public object EventArgsConverterParameter               get   return  object GetValue EventArgsConverterParameterProperty             set   SetValue EventArgsConverterParameterProperty  value                public static readonly DependencyProperty EventArgsConverterParameterProperty           DependencyProperty Register  EventArgsConverterParameter   typeof object   typeof EventCommandExecuter   new PropertyMetadata null          endregion      public IValueConverter EventArgsConverter   get  set         public CultureInfo Culture   get  set          endregion      protected override void Invoke object parameter                var cmd   Command           if  cmd    null                        var param   parameter               if  EventArgsConverter    null                                param   EventArgsConverter Convert parameter  typeof object   EventArgsConverterParameter  CultureInfo InvariantCulture                              if  cmd CanExecute param                                 cmd Execute param                                     This class has two dependency properties  one to allow binding to your view model s command  the other allows you to bind the source of the event if you need it during event args conversion  You can also provide culture settings if you need to  they default to the current UI culture    This class allows you to adapt the event args so that they may be consumed by your view model s command logic  However  if you want to just pass the event args on verbatim  simply don t specify an event args converter   The simplest usage of this trigger action in XAML is as follows    lt i Interaction Triggers gt       lt i EventTrigger EventName  NameChanged  gt           lt cmd EventCommandExecuter Command   Binding Path Update  Mode OneTime   EventArgsConverter   x Static c NameChangedArgsToStringConverter Default    gt       lt  i EventTrigger gt   lt  i Interaction Triggers gt    If you needed access to the source of the event  you would bind to the owner of the event   lt i Interaction Triggers gt       lt i EventTrigger EventName  NameChanged  gt           lt cmd EventCommandExecuter              Command   Binding Path Update  Mode OneTime                EventArgsConverter   x Static c NameChangedArgsToStringConverter Default               EventArgsConverterParameter   Binding ElementName SomeEventSource  Mode OneTime    gt       lt  i EventTrigger gt   lt  i Interaction Triggers gt     this assumes that the XAML node you re attaching the triggers to has been assigned x Name  SomeEventSource   This XAML relies on importing some required namespaces  xmlns cmd  clr-namespace MyProject WPF Commands  xmlns c  clr-namespace MyProject WPF Converters  xmlns i  clr-namespace System Windows Interactivity assembly System Windows Interactivity    and creating an IValueConverter  called NameChangedArgsToStringConverter in this case  to handle the actual conversion logic  For basic converters I usually create a default static readonly converter instance  which I can then reference directly in XAML as I have done above   The benefit of this solution is that you really only need to add a single class to any project to use the interaction framework much the same way that you would use it with InvokeCommandAction  Adding a single class  of about 75 lines  should be much more preferable to an entire library to accomplish identical results   NOTE  this is somewhat similar to the answer from  adabyron but it uses event triggers instead of behaviours  This solution also provides an event args conversion ability  not that  adabyron s solution could not do this as well  I really don t have any good reason why I prefer triggers to behaviours  just a personal choice  IMO either strategy is a reasonable choice

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I try to keep my dependencies to a minimum  so I implemented this myself instead of going with EventToCommand of MVVMLight  Works for me so far  but feedback is welcome   Xaml    lt i Interaction Behaviors gt       lt beh EventToCommandBehavior Command   Binding DropCommand   Event  Drop  PassArguments  True    gt   lt  i Interaction Behaviors gt    ViewModel   public ActionCommand lt DragEventArgs gt  DropCommand   get  private set     this DropCommand   new ActionCommand lt DragEventArgs gt  OnDrop    private void OnDrop DragEventArgs e                   EventToCommandBehavior        lt summary gt      Behavior that will connect an UI event to a viewmodel Command      allowing the event arguments to be passed as the CommandParameter       lt  summary gt  public class EventToCommandBehavior   Behavior lt FrameworkElement gt        private Delegate  handler      private EventInfo  oldEvent          Event     public string Event   get   return  string GetValue EventProperty     set   SetValue EventProperty  value           public static readonly DependencyProperty EventProperty   DependencyProperty Register  Event   typeof string   typeof EventToCommandBehavior   new PropertyMetadata null  OnEventChanged            Command     public ICommand Command   get   return  ICommand GetValue CommandProperty     set   SetValue CommandProperty  value           public static readonly DependencyProperty CommandProperty   DependencyProperty Register  Command   typeof ICommand   typeof EventToCommandBehavior   new PropertyMetadata null            PassArguments  default  false      public bool PassArguments   get   return  bool GetValue PassArgumentsProperty     set   SetValue PassArgumentsProperty  value           public static readonly DependencyProperty PassArgumentsProperty   DependencyProperty Register  PassArguments   typeof bool   typeof EventToCommandBehavior   new PropertyMetadata false          private static void OnEventChanged DependencyObject d  DependencyPropertyChangedEventArgs e                var beh    EventToCommandBehavior d           if  beh AssociatedObject    null     is not yet attached at initial load             beh AttachHandler  string e NewValue              protected override void OnAttached                 AttachHandler this Event      initial set                 lt summary gt          Attaches the handler to the event          lt  summary gt      private void AttachHandler string eventName                   detach old event         if   oldEvent    null               oldEvent RemoveEventHandler this AssociatedObject   handler               attach new event         if   string IsNullOrEmpty eventName                         EventInfo ei   this AssociatedObject GetType   GetEvent eventName               if  ei    null                                MethodInfo mi   this GetType   GetMethod  ExecuteCommand   BindingFlags Instance   BindingFlags NonPublic                    handler   Delegate CreateDelegate ei EventHandlerType  this  mi                   ei AddEventHandler this AssociatedObject   handler                    oldEvent   ei     store to detach in case the Event property changes                           else                 throw new ArgumentException string Format  The event   0   was not found on type   1     eventName  this AssociatedObject GetType   Name                              lt summary gt          Executes the Command          lt  summary gt      private void ExecuteCommand object sender  EventArgs e                object parameter   this PassArguments   e   null          if  this Command    null                        if  this Command CanExecute parameter                   this Command Execute parameter                       ActionCommand   public class ActionCommand lt T gt    ICommand       public event EventHandler CanExecuteChanged      private Action lt T gt   action       public ActionCommand Action lt T gt  action                 action   action             public bool CanExecute object parameter    return true         public void Execute object parameter                if   action    null                        var castParameter    T Convert ChangeType parameter  typeof T                 action castParameter

User · Answer

What I do is to use InvokeCommandAction to bind the control loaded event to a command in the view model  give the control a x Name in Xaml and pass as CommandParameter  then in said loaded command hook view model handlers up to the events where I need to get the event args

User · Answer

With Behaviors and Actions in Blend for Visual Studio 2013 you can use the InvokeCommandAction  I tried this with the Drop event and although no CommandParameter was specified in the XAML  to my surprise  the Execute Action parameter contained the DragEventArgs  I presume this would happen for other events but have not tested them

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I know it s a bit late but  Microsoft has made their Xaml Behaviors open source and it s now much easier to use interactivity with just one namespace   First add Microsoft Xaml Behaviors Wpf Nuget packge to your project  https   www nuget org packages Microsoft Xaml Behaviors Wpf  add xmlns behaviours  quot http   schemas microsoft com xaml behaviors quot  namespace to your xaml   Then use it like this   lt Button Width  quot 150 quot  Style  quot  DynamicResource MaterialDesignRaisedDarkButton  quot  gt      lt behaviours Interaction Triggers gt          lt behaviours EventTrigger EventName  quot Click quot  gt              lt behaviours InvokeCommandAction Command  quot  Binding OpenCommand  quot  PassEventArgsToCommand  quot True quot   gt          lt  behaviours EventTrigger gt       lt  behaviours Interaction Triggers gt      Open  lt  Button gt   PassEventArgsToCommand  quot True quot  should be set as True and the RelayCommand that you implement can take RoutedEventArgs or objects as template  If you are using object as the parameter type just cast it to the appropriate event type  The command will look something like this  OpenCommand   new RelayCommand lt object gt  OnOpenClicked   o    gt    return true       The command method will look something like this  private void OnOpenClicked object parameter        Logger Info parameter  GetType   Name      The  parameter  will be the Routed event object  And the log incase you are curious  2020-12-15 11 40 36 3600 INFO MyApplication ViewModels MainWindowViewModel RoutedEventArgs As you can see the TypeName logged is RoutedEventArgs RelayCommand impelmentation can be found here  Why RelayCommand PS   You can bind to any event of any control  Like Closing event of Window and you will get the corresponding events

User · Answer

It s not easily supported  Here s an article with instructions on how to pass EventArgs as command parameters   You might want to look into using MVVMLight - it supports EventArgs in command directly  your situation would look something like this     lt i Interaction Triggers gt       lt i EventTrigger EventName  Navigated  gt           lt cmd EventToCommand Command   Binding NavigatedEvent               PassEventArgsToCommand  True    gt       lt  i EventTrigger gt    lt  i Interaction Triggers gt

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Here is a version of  adabyron s answer that prevents the leaky EventArgs abstraction   First  the modified EventToCommandBehavior class  now a generic abstract class and formatted with ReSharper code cleanup   Note the new GetCommandParameter virtual method and its default implementation   public abstract class EventToCommandBehavior lt TEventArgs gt    Behavior lt FrameworkElement gt      where TEventArgs   EventArgs       public static readonly DependencyProperty EventProperty   DependencyProperty Register  Event   typeof string   typeof EventToCommandBehavior lt TEventArgs gt    new PropertyMetadata null  OnEventChanged        public static readonly DependencyProperty CommandProperty   DependencyProperty Register  Command   typeof ICommand   typeof EventToCommandBehavior lt TEventArgs gt    new PropertyMetadata null        public static readonly DependencyProperty PassArgumentsProperty   DependencyProperty Register  PassArguments   typeof bool   typeof EventToCommandBehavior lt TEventArgs gt    new PropertyMetadata false        private Delegate  handler      private EventInfo  oldEvent       public string Event               get   return  string GetValue EventProperty             set   SetValue EventProperty  value                public ICommand Command               get   return  ICommand GetValue CommandProperty             set   SetValue CommandProperty  value                public bool PassArguments               get   return  bool GetValue PassArgumentsProperty             set   SetValue PassArgumentsProperty  value                protected override void OnAttached                 AttachHandler Event              protected virtual object GetCommandParameter TEventArgs e                return e             private void AttachHandler string eventName                 oldEvent  RemoveEventHandler AssociatedObject   handler            if  string IsNullOrEmpty eventName                         return                     EventInfo eventInfo   AssociatedObject GetType   GetEvent eventName            if  eventInfo    null                        MethodInfo methodInfo   typeof EventToCommandBehavior lt TEventArgs gt   GetMethod  ExecuteCommand   BindingFlags Instance   BindingFlags NonPublic                 handler   Delegate CreateDelegate eventInfo EventHandlerType  this  methodInfo               eventInfo AddEventHandler AssociatedObject   handler                oldEvent   eventInfo                    else                       throw new ArgumentException   The event   eventName   was not found on type   AssociatedObject GetType   FullName                            private static void OnEventChanged DependencyObject d  DependencyPropertyChangedEventArgs e                var behavior    EventToCommandBehavior lt TEventArgs gt  d           if  behavior AssociatedObject    null                        behavior AttachHandler  string e NewValue                           ReSharper disable once UnusedMember Local        ReSharper disable once UnusedParameter Local     private void ExecuteCommand object sender  TEventArgs e                object parameter   PassArguments   GetCommandParameter e    null           if  Command  CanExecute parameter     true                        Command Execute parameter                       Next  an example derived class that hides DragCompletedEventArgs  Some people expressed concern about leaking the EventArgs abstraction into their view model assembly  To prevent this  I created an interface that represents the values we care about  The interface can live in the view model assembly with the private implementation in the UI assembly      UI assembly public class DragCompletedBehavior   EventToCommandBehavior lt DragCompletedEventArgs gt        protected override object GetCommandParameter DragCompletedEventArgs e                return new DragCompletedArgs e              private class DragCompletedArgs   IDragCompletedArgs               public DragCompletedArgs DragCompletedEventArgs e                        Canceled   e Canceled              HorizontalChange   e HorizontalChange              VerticalChange   e VerticalChange                     public bool Canceled   get            public double HorizontalChange   get            public double VerticalChange   get                View model assembly public interface IDragCompletedArgs       bool Canceled   get        double HorizontalChange   get        double VerticalChange   get        Cast the command parameter to IDragCompletedArgs  similar to  adabyron s answer

User · Answer

As an adaption of  Mike Fuchs answer  here s an even smaller solution  I m using the Fody AutoDependencyPropertyMarker to reduce some of the boiler plate   The Class  public class EventCommand   TriggerAction lt DependencyObject gt         AutoDependencyProperty      public ICommand Command   get  set         protected override void Invoke object parameter                if  Command    null                        if  Command CanExecute parameter                                 Command Execute parameter                                     The EventArgs  public class VisibleBoundsArgs   EventArgs       public Rect VisibleVounds   get         public VisibleBoundsArgs Rect visibleBounds                VisibleVounds   visibleBounds            The XAML   lt local ZoomableImage gt      lt i Interaction Triggers gt         lt i EventTrigger EventName  VisibleBoundsChanged   gt            lt local EventCommand Command   Binding VisibleBoundsChanged     gt         lt  i EventTrigger gt      lt  i Interaction Triggers gt   lt  local ZoomableImage gt    The ViewModel  public ICommand VisibleBoundsChanged   gt   visibleBoundsChanged                                              visibleBoundsChanged   new RelayCommand obj   gt  SetVisibleBounds   VisibleBoundsArgs obj  VisibleVounds

User · Answer

To add to what joshb has stated already - this works just fine for me  Make sure to add references to Microsoft Expression Interactions dll and System Windows Interactivity dll and in your xaml do        xmlns i  http   schemas microsoft com expression 2010 interactivity    I ended up using something like this for my needs  This shows that you can also pass a custom parameter    lt i Interaction Triggers gt               lt i EventTrigger EventName  SelectionChanged  gt                    lt i InvokeCommandAction Command   Binding Path DataContext RowSelectedItem  RelativeSource  RelativeSource AncestorType  x Type Window                                             CommandParameter   Binding Path SelectedItem  RelativeSource  RelativeSource Mode FindAncestor  AncestorType DataGrid      gt               lt  i EventTrigger gt   lt  i Interaction Triggers gt

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I don t think you can do that easily with the InvokeCommandAction - I would take a look at EventToCommand from MVVMLight or similar

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For people just finding this post  you should know that in newer versions  not sure on the exact version since official docs are slim on this topic  the default behavior of the InvokeCommandAction  if no CommandParameter is specified  is to pass the args of the event it s attached to as the CommandParameter  So the originals poster s XAML could be simply written as    lt i Interaction Triggers gt     lt i EventTrigger EventName  Navigated  gt       lt i InvokeCommandAction Command   Binding NavigatedEvent    gt     lt  i EventTrigger gt   lt  i Interaction Triggers gt    Then in your command  you can accept a parameter of type NavigationEventArgs  or whatever event args type is appropriate  and it will automatically be provided

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I ve always come back here for the answer so I wanted to make a short simple one to go to   There are multiple ways of doing this   1  Using WPF Tools  Easiest   Add Namespaces    System Windows Interactivitiy Microsoft Expression Interactions   XAML   Use the EventName to call the event you want then specify your Method name in the MethodName    lt Window gt      xmlns wi  clr-namespace System Windows Interactivity assembly System Windows Interactivity      xmlns ei  http   schemas microsoft com expression 2010 interactions  gt        lt wi Interaction Triggers gt           lt wi EventTrigger EventName  SelectionChanged  gt               lt ei CallMethodAction                 TargetObject   Binding                   MethodName  ShowCustomer   gt           lt  wi EventTrigger gt       lt  wi Interaction Triggers gt   lt  Window gt    Code   public void ShowCustomer            Do something        2  Using MVVMLight  Most difficult   Install GalaSoft NuGet package     Get the namespaces    System Windows Interactivity GalaSoft MvvmLight Platform   XAML   Use the EventName to call the event you want then specify your Command name in your binding  If you want to pass the arguments of the method  mark PassEventArgsToCommand to true    lt Window gt      xmlns wi  clr-namespace System Windows Interactivity assembly System Windows Interactivity      xmlns cmd  http   www galasoft ch mvvmlight  gt        lt wi Interaction Triggers gt          lt wi EventTrigger EventName  Navigated  gt              lt cmd EventToCommand Command   Binding CommandNameHere                  PassEventArgsToCommand  True    gt          lt  wi EventTrigger gt       lt  wi Interaction Triggers gt   lt  Window gt    Code Implementing Delegates  Source  You must get the Prism MVVM NuGet package for this     using Microsoft Practices Prism Commands      With params  public DelegateCommand lt string gt  CommandOne   get  set       Without params  public DelegateCommand CommandTwo   get  set     public MainWindow         InitializeComponent            Must initialize the DelegateCommands here      CommandOne   new DelegateCommand lt string gt  executeCommandOne       CommandTwo   new DelegateCommand executeCommandTwo      private void executeCommandOne string param           Do something here     private void executeCommandTwo            Do something here      Code Without DelegateCommand  Source  using GalaSoft MvvmLight CommandWpf  public MainWindow         InitializeComponent         CommandOne   new RelayCommand lt string gt  executeCommandOne       CommandTwo   new RelayCommand executeCommandTwo      public RelayCommand lt string gt  CommandOne   get  set     public RelayCommand CommandTwo   get  set     private void executeCommandOne string param           Do something here     private void executeCommandTwo            Do something here        3  Using Telerik EventToCommandBehavior  It s an option   You ll have to download it s NuGet Package   XAML    lt i Interaction Behaviors gt       lt telerek EventToCommandBehavior          Command   Binding DropCommand            Event  Drop           PassArguments  True    gt   lt  i Interaction Behaviors gt    Code   public ActionCommand lt DragEventArgs gt  DropCommand   get  private set     this DropCommand   new ActionCommand lt DragEventArgs gt  OnDrop    private void OnDrop DragEventArgs e           Do Something

[wpf] MVVM Passing EventArgs As Command Parameter

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