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CommandBinding Class

Binds a RoutedCommand to the event handlers that implement the command.

Namespace:  System.Windows.Input
Assembly:  PresentationCore (in PresentationCore.dll)
XMLNS for XAML: http://schemas.microsoft.com/winfx/2006/xaml/presentation, http://schemas.microsoft.com/netfx/2007/xaml/presentation

public class CommandBinding
<CommandBinding .../>

A CommandBinding associates a command with the PreviewExecuted/Executed and PreviewCanExecute/CanExecute events which implement and determine the status of the command.

When the Execute or CanExecute method of a RoutedCommand is called, the PreviewExecuted/Executed or the PreviewCanExecute/CanExecute events are raised on the command target. If the command target has a CommandBinding for the command, the appropriate handlers are called. If the command target does not have a CommandBinding for the command, the events are routed through the element tree until an element that has a CommandBinding is found.

A CommandBinding has limited use with an ICommand that is not a RoutedCommand. This is because a CommandBinding binds the command to the ExecutedRoutedEventHandler and the CanExecuteRoutedEventHandler which listen to the Executed and CanExecute routed events which are raised when the Execute and CanExecute method of the RoutedCommand are called.

The following example demonstrates how to use commanding in Windows Presentation Foundation (WPF). The example shows how to associate a RoutedCommand to a Button, create a CommandBinding, and create the event handlers which implement the RoutedCommand. For more information on commanding, see the Commanding Overview.

The first section of code creates the user interface (UI), which consists of a Button and a StackPanel, and creates a CommandBinding that associates the command handlers with the RoutedCommand.

The Command property of the Button is associated with the Close command.

The CommandBinding is added to the CommandBindingCollection of the root Window. The Executed and CanExecute event handlers are attached to this binding and associated with the Close command.

Without the CommandBinding there is no command logic, only a mechanism to invoke the command. When the Button is clicked, the PreviewExecuted RoutedEvent is raised on the command target followed by the Executed RoutedEvent. These events traverse the element tree looking for a CommandBinding for that particular command. It is worth noting that because RoutedEvent tunnel and bubble through the element tree, care must be taken in where the CommandBinding is put. If the CommandBinding is on a sibling of the command target or another node that is not on the route of the RoutedEvent, the CommandBinding will not be accessed.

<Window x:Class="WCSamples.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="CloseCommand"
    Name="RootWindow"
    >
  <Window.CommandBindings>
    <CommandBinding Command="ApplicationCommands.Close"
                    Executed="CloseCommandHandler"
                    CanExecute="CanExecuteHandler"
                    />
  </Window.CommandBindings>
  <StackPanel Name="MainStackPanel">
    <Button Command="ApplicationCommands.Close" 
            Content="Close File" />
  </StackPanel>
</Window>
// Create ui elements.
StackPanel CloseCmdStackPanel = new StackPanel();
Button CloseCmdButton = new Button();
CloseCmdStackPanel.Children.Add(CloseCmdButton);

// Set Button's properties.
CloseCmdButton.Content = "Close File";
CloseCmdButton.Command = ApplicationCommands.Close;

// Create the CommandBinding.
CommandBinding CloseCommandBinding = new CommandBinding(
    ApplicationCommands.Close, CloseCommandHandler, CanExecuteHandler);

// Add the CommandBinding to the root Window.
RootWindow.CommandBindings.Add(CloseCommandBinding);

The next section of code implements the Executed and CanExecute event handlers.

The Executed handler calls a method to close the open file. The CanExecute handler calls a method to determine whether a file is open. If a file is open, CanExecute is set to true; otherwise, it is set to false.

// Executed event handler. 
private void CloseCommandHandler(object sender, ExecutedRoutedEventArgs e)
{
    // Calls a method to close the file and release resources.
    CloseFile();
}

// CanExecute event handler. 
private void CanExecuteHandler(object sender, CanExecuteRoutedEventArgs e)
{
    // Call a method to determine if there is a file open. 
    // If there is a file open, then set CanExecute to true. 
    if (IsFileOpened())
    {
        e.CanExecute = true;
    }
    // if there is not a file open, then set CanExecute to false. 
    else
    {
        e.CanExecute = false;
    }
}

System.Object
  System.Windows.Input.CommandBinding

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 7, Windows Vista, Windows XP SP2, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0

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