Hook Up a Command to a Control with Command Support

How to: Hook Up a Command to a Control with Command Support

 

The following example shows how to hook up a RoutedCommand to a Control which has 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.

Example

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. Some controls have built in CommandBindings for some commands. This mechanism allows the semantics of a command to stay the same, while the actual implementation is can change. A TextBox, for example, handles the Paste command differently than a control designed to support images, but the basic idea of what it means to paste something stays the same. The command logic cannot be supplied by the command, but rather must be supplied by the control or the application.

Many controls in WPF do 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 MenuItem as the command source for the Paste command, where a TextBox is the target of the command. All the logic that defines how the TextBox performs the paste is built into the TextBox control.

A MenuItem is created and it's Command property is set to the Paste command. The CommandTarget is not explicitly set to the TextBox object. When the CommandTarget is not set, the target for the command is the element which has keyboard focus. If the element which has keyboard focus does not support the Paste command or cannot currently execute the paste command (the clipboard is empty, for example) then the MenuItem would be grayed out.

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