ComponentCommands Class

The commands in the ComponentCommands class and commands in the other command library classes, such as ApplicationCommands and NavigationCommands, are intended to represent a set of common commands that application programmers encounter frequently. The commands only represent the instance of the RoutedCommand and not the implementation logic for the command. The implementation logic is bound to the command via a CommandBindings. For example, if the MoveLeft command is executed on a control (the command target), the logic that performs the MoveLeft command may not be provided by the command target, so the application writer is responsible for writing the logic that determines how the command target handles the command.

Many controls do provide implementation logic, though, for many of the commands in the command library. For example, the TextBox class provides logic for the Paste command, Cut command, Copy command, Undo command, and Redo command. See the class documentation for particular control classes for more information.

For more information on commands and commanding, see Commanding Overview.

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.

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.

<Window x:Class="SDKSamples.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MenuItemCommandTask"
    >
    <DockPanel>
      <Menu DockPanel.Dock="Top">
        <MenuItem Command="ApplicationCommands.Paste" Width="75" />
      </Menu>
      <TextBox BorderBrush="Black" BorderThickness="2" Margin="25"
               TextWrapping="Wrap">
        The MenuItem will not be enabled until
        this TextBox gets keyboard focus  
      </TextBox>
    </DockPanel>
</Window>

// Window1 constructor
public Window1()
{
    InitializeComponent();

    // Instantiating UIElements.
    DockPanel mainPanel = new DockPanel();
    Menu mainMenu = new Menu();
    MenuItem pasteMenuItem = new MenuItem();
    TextBox mainTextBox = new TextBox();

    // Associating the MenuItem with the Paste command.
    pasteMenuItem.Command = ApplicationCommands.Paste;

    // Setting properties on the TextBox.
    mainTextBox.Text =
        "The MenuItem will not be enabled until this TextBox receives keyboard focus.";
    mainTextBox.Margin = new Thickness(25);
    mainTextBox.BorderBrush = Brushes.Black;
    mainTextBox.BorderThickness = new Thickness(2);
    mainTextBox.TextWrapping = TextWrapping.Wrap;

    // Attaching UIElements to the Window.
    this.AddChild(mainPanel);
    mainMenu.Items.Add(pasteMenuItem);
    mainPanel.Children.Add(mainMenu);
    mainPanel.Children.Add(mainTextBox);

    // Defining DockPanel layout.
    DockPanel.SetDock(mainMenu, Dock.Top);
    DockPanel.SetDock(mainTextBox, Dock.Bottom);
}

More Code

.NET Framework

.NET Framework Client Profile

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

Reference

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