如何：启用命令

下面的示例演示如何在 Windows Presentation Foundation (WPF) 中使用命令设置功能。 该示例演示如何将 RoutedCommand 与 Button 关联，如何创建 CommandBinding，以及如何创建实现 RoutedCommand 的事件处理程序。 有关设置命令的更多信息，请参见命令概述。

示例

代码的第一部分创建由 Button 和 StackPanel 组成的user interface (UI)，并创建一个将命令处理程序与 RoutedCommand 关联的 CommandBinding。

Button 的 Command 属性与 Close 命令关联。

CommandBinding 添加到根 Window 的 CommandBindingCollection 中。 Executed 和 CanExecute 事件处理程序附加到此绑定并与 Close 命令关联。

没有 CommandBinding 就没有命令逻辑，而只是存在调用命令的机制。 在单击 Button 时，会针对命令目标引发 PreviewExecuted RoutedEvent，之后将引发 Executed RoutedEvent。 这些事件会遍历元素树，以查找该特定命令的 CommandBinding。 值得注意的是，由于 RoutedEvent 会在元素树中执行隧道和冒泡操作，因此一定要注意 CommandBinding 的放置位置。 如果 CommandBinding 位于命令目标的同级，或者它所在的节点不在 RoutedEvent 的路由上，将不会访问 CommandBinding。

<Window x:Class="WCSamples.Window1"
    xmlns="https://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="https://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.
            Dim CloseCmdStackPanel As New StackPanel()
            Dim CloseCmdButton As New Button()
            CloseCmdStackPanel.Children.Add(CloseCmdButton)

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

            ' Create the CommandBinding.
            Dim CloseCommandBinding As New CommandBinding(ApplicationCommands.Close, AddressOf CloseCommandHandler, AddressOf CanExecuteHandler)

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

// 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);

代码的第二部分实现 Executed 和 CanExecute 事件处理程序。

Executed 处理程序调用一个方法来关闭已打开的文件。 CanExecute 处理程序调用一个方法来确定文件是否处于打开状态。 如果文件处于打开状态，CanExecute 将设置为 true；否则将设置为 false。

        ' Executed event handler.
        Private Sub CloseCommandHandler(ByVal sender As Object, ByVal e As ExecutedRoutedEventArgs)
            ' Calls a method to close the file and release resources.
            CloseFile()
        End Sub

        ' CanExecute event handler.
        Private Sub CanExecuteHandler(ByVal sender As Object, ByVal e As CanExecuteRoutedEventArgs)
            ' Call a method to determine if there is a file open.
            ' If there is a file open, then set CanExecute to true.
            If IsFileOpened() Then
                e.CanExecute = True
            ' if there is not a file open, then set CanExecute to false.
            Else
                e.CanExecute = False
            End If
        End Sub

// 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;
    }
}

请参见

概念

命令概述