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How to: Create a RoutedCommand

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This example shows how to create a custom RoutedCommand and how to implement the custom command by creating a ExecutedRoutedEventHandler and a CanExecuteRoutedEventHandler and attaching them to a CommandBinding. For more information on commanding, see the Commanding Overview.

Example

The first step in creating a RoutedCommand is defining the command and instantiating it.

public static RoutedCommand CustomRoutedCommand = new RoutedCommand();

Public Shared CustomRoutedCommand As New RoutedCommand()

In order to use the command in an application, event handlers which define what the command does must be created

private void ExecutedCustomCommand(object sender,
    ExecutedRoutedEventArgs e)
{
    MessageBox.Show("Custom Command Executed");
}

Private Sub ExecutedCustomCommand(ByVal sender As Object, ByVal e As ExecutedRoutedEventArgs)
    MessageBox.Show("Custom Command Executed")
End Sub

// CanExecuteRoutedEventHandler that only returns true if
// the source is a control.
private void CanExecuteCustomCommand(object sender,
    CanExecuteRoutedEventArgs e)
{
    Control target = e.Source as Control;

    if(target != null)
    {
        e.CanExecute = true;
    }
    else
    {
        e.CanExecute = false;
    }
}

' CanExecuteRoutedEventHandler that only returns true if
' the source is a control.
Private Sub CanExecuteCustomCommand(ByVal sender As Object, ByVal e As CanExecuteRoutedEventArgs)
    Dim target As Control = TryCast(e.Source, Control)

    If target IsNot Nothing Then
        e.CanExecute = True
    Else
        e.CanExecute = False
    End If
End Sub

Next, a CommandBinding is created which associates the command with the event handlers. The CommandBinding is created on a specific object. This object defines the scope of the CommandBinding in the element tree

<Window x:Class="SDKSamples.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:custom="clr-namespace:SDKSamples"
    Height="600" Width="800"
    >
  <Window.CommandBindings>
    <CommandBinding Command="{x:Static custom:Window1.CustomRoutedCommand}"
                    Executed="ExecutedCustomCommand"
                    CanExecute="CanExecuteCustomCommand" />
  </Window.CommandBindings>

CommandBinding customCommandBinding = new CommandBinding(
    CustomRoutedCommand, ExecutedCustomCommand, CanExecuteCustomCommand);

// attach CommandBinding to root window
this.CommandBindings.Add(customCommandBinding);

Dim customCommandBinding As New CommandBinding(CustomRoutedCommand, AddressOf ExecutedCustomCommand, AddressOf CanExecuteCustomCommand)

' attach CommandBinding to root window
Me.CommandBindings.Add(customCommandBinding)

The final step is invoking the command. One way to invoke a command is to associate it with a ICommandSource, such as a Button.

<StackPanel>
  <Button Command="{x:Static custom:Window1.CustomRoutedCommand}"
          Content="CustomRoutedCommand"/>
</StackPanel>

// create the ui
StackPanel CustomCommandStackPanel = new StackPanel();
Button CustomCommandButton = new Button();
CustomCommandStackPanel.Children.Add(CustomCommandButton);

CustomCommandButton.Command = CustomRoutedCommand;

' create the ui
Dim CustomCommandStackPanel As New StackPanel()
Dim CustomCommandButton As New Button()
CustomCommandStackPanel.Children.Add(CustomCommandButton)

CustomCommandButton.Command = CustomRoutedCommand

When the Button is clicked, the Execute method on the custom RoutedCommand is called. The RoutedCommand raises the PreviewExecuted and Executed routed events. These events traverse the element tree looking for a CommandBinding for this particular command. If a CommandBinding is found, the ExecutedRoutedEventHandler associated with CommandBinding is called.

See also