RoutedCommand.CanExecute(Object, IInputElement) Method

public:
 bool CanExecute(System::Object ^ parameter, System::Windows::IInputElement ^ target);

[System.Security.SecurityCritical]
public bool CanExecute(object parameter, System.Windows.IInputElement target);

public bool CanExecute(object parameter, System.Windows.IInputElement target);

[<System.Security.SecurityCritical>]
member this.CanExecute : obj * System.Windows.IInputElement -> bool

member this.CanExecute : obj * System.Windows.IInputElement -> bool

Public Function CanExecute (parameter As Object, target As IInputElement) As Boolean

Parameters

Returns

true if the command can execute on the current command target; otherwise, false.

Attributes

SecurityCriticalAttribute

Exceptions

Examples

The following example is a CanExecuteChanged event handler from a custom implementation of ICommandSource.

this.Command in this example is the Command property on the ICommandSource. If the command is not null, the command is cast to a RoutedCommand. If the command is a RoutedCommand, then the CanExecute method is called passing the CommandTarget and the CommandParameter. If command is not a RoutedCommand, it is cast to an ICommand and the CanExecute method is called passing the CommandParameter.

If the CanExecute method returns true, then the control is enabled; otherwise, the control is disable.

private void CanExecuteChanged(object sender, EventArgs e)
{

 if (this.Command != null)
 {
 RoutedCommand command = this.Command as RoutedCommand;

 // If a RoutedCommand.
 if (command != null)
 {
 if (command.CanExecute(CommandParameter, CommandTarget))
 {
 this.IsEnabled = true;
 }
 else
 {
 this.IsEnabled = false;
 }
 }
 // If a not RoutedCommand.
 else
 {
 if (Command.CanExecute(CommandParameter))
 {
 this.IsEnabled = true;
 }
 else
 {
 this.IsEnabled = false;
 }
 }
 }
}

Private Sub CanExecuteChanged(ByVal sender As Object, ByVal e As EventArgs)

 If Me.Command IsNot Nothing Then
 Dim command As RoutedCommand = TryCast(Me.Command, RoutedCommand)

 ' If a RoutedCommand.
 If command IsNot Nothing Then
 If command.CanExecute(CommandParameter, CommandTarget) Then
 Me.IsEnabled = True
 Else
 Me.IsEnabled = False
 End If
 ' If a not RoutedCommand.
 Else
 If Me.Command.CanExecute(CommandParameter) Then
 Me.IsEnabled = True
 Else
 Me.IsEnabled = False
 End If
 End If
 End If
End Sub

Remarks

The actual logic that determines if a RoutedCommand can execute on the current command target is not contained in the CanExecute methods, rather CanExecute raises the PreviewCanExecute and the CanExecute events which tunnel and bubble through element tree looking for a object with a CommandBinding. If a CommandBinding for that RoutedCommand is found, then the CanExecuteRoutedEventHandler attached to CommandBinding is called. These handlers supply the programming logic for determining if the RoutedCommand can execute or not.

The PreviewCanExecute and PreviewExecuted events are raised on the CommandTarget. If the CommandTarget is not set on the ICommandSource, the PreviewCanExecute and CanExecute events are raised on the element with keyboard focus.