How to: Hook Up a Command to a Control with No Command Support

The following example shows how to hook up a RoutedCommand to a Control which does not have built in support for the command. For a complete sample which hooks up commands to multiple sources, see the Create a Custom RoutedCommand Sample sample.

Windows Presentation Foundation (WPF) provides a library of common commands which application programmers encounter regularly. The classes which comprise the command library are: ApplicationCommands, ComponentCommands, NavigationCommands, MediaCommands, and EditingCommands.

The static RoutedCommand objects which make up these classes do not supply command logic. The logic for the command is associated with the command with a CommandBinding. Many controls in WPF have built in support for some of the commands in the command library. TextBox, for example, supports many of the application edit commands such as Paste, Copy, Cut, Redo, and Undo. The application developer does not have to do anything special to get these commands to work with these controls. If the TextBox is the command target when the command is executed, it will handle the command using the CommandBinding that is built into the control.

The following shows how to use a Button as the command source for the Open command. A CommandBinding is created that associates the specified CanExecuteRoutedEventHandler and the CanExecuteRoutedEventHandler with the RoutedCommand.

First, the command source is created. A Button is used as the command source.

<Button Command="ApplicationCommands.Open" Name="MyButton"
        Height="50" Width="200">
  Open (KeyBindings: Ctrl+R, Ctrl+0)
</Button>
			' Button used to invoke the command
			Dim CommandButton As New Button()
			CommandButton.Command = ApplicationCommands.Open
			CommandButton.Content = "Open (KeyBindings: Ctrl-R, Ctrl-0)"
			MainStackPanel.Children.Add(CommandButton)

Next, the ExecutedRoutedEventHandler and the CanExecuteRoutedEventHandler are created. The ExecutedRoutedEventHandler simply opens a MessageBox to signify that the command executed. The CanExecuteRoutedEventHandler sets the CanExecute property to true. Normally, the can execute handler would perform more robust checks to see if the command could execute on the current command target.


        Private Sub OpenCmdExecuted(ByVal sender As Object, ByVal e As ExecutedRoutedEventArgs)
            Dim command, targetobj As String
            command = CType(e.Command, RoutedCommand).Name
            targetobj = CType(sender, FrameworkElement).Name
            MessageBox.Show("The " + command + " command has been invoked on target object " + targetobj)
        End Sub 
        Private Sub OpenCmdCanExecute(ByVal sender As Object, ByVal e As CanExecuteRoutedEventArgs)
            e.CanExecute = True 
        End Sub

Finally, a CommandBinding is created on the root Window of the application that associates the routed events handlers to the Open command.

<Window.CommandBindings>
  <CommandBinding Command="ApplicationCommands.Open"
                  Executed="OpenCmdExecuted"
                  CanExecute="OpenCmdCanExecute"/>
</Window.CommandBindings>
			' Creating CommandBinding and attaching an Executed and CanExecute handler
			Dim OpenCmdBinding As New CommandBinding(ApplicationCommands.Open, AddressOf OpenCmdExecuted, AddressOf OpenCmdCanExecute)

			Me.CommandBindings.Add(OpenCmdBinding)
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