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Keyboard.LostKeyboardFocus 附加事件

  • 参考

定义

命名空间:
System.Windows.Input
程序集:
PresentationCore.dll

在元素丢失键盘焦点时发生。

see AddLostKeyboardFocusHandler, and RemoveLostKeyboardFocusHandler
see AddLostKeyboardFocusHandler, and RemoveLostKeyboardFocusHandler
see AddLostKeyboardFocusHandler, and RemoveLostKeyboardFocusHandler

示例

以下示例创建 并TextBox附加 事件和 LostKeyboardFocus 事件的事件处理程序GotKeyboardFocus。 TextBox当 获得键盘焦点时，背景色将更改并清除 的文本TextBox。 TextBlock当 失去键盘焦点时，背景色将更改，并调用重置示例中使用的变量的方法。

<Border BorderBrush="Black" BorderThickness="1"
        Width="200" Height="100" Margin="5">
  <StackPanel>
    <Label HorizontalAlignment="Center" Content="Type Text In This TextBox" />
    <TextBox Width="175"
             Height="50" 
             Margin="5"
             TextWrapping="Wrap"
             HorizontalAlignment="Center"
             VerticalScrollBarVisibility="Auto"
             GotKeyboardFocus="TextBoxGotKeyboardFocus"
             LostKeyboardFocus="TextBoxLostKeyboardFocus"
             KeyDown="SourceTextKeyDown"/>
  </StackPanel>
</Border>

private void TextBoxGotKeyboardFocus(object sender, KeyboardFocusChangedEventArgs e)
{
    TextBox source = e.Source as TextBox;

    if (source != null)
    {
        // Change the TextBox color when it obtains focus.
        source.Background = Brushes.LightBlue;

        // Clear the TextBox.
        source.Clear();
    }
}

Private Sub TextBoxGotKeyboardFocus(ByVal sender As Object, ByVal e As KeyboardFocusChangedEventArgs)
    Dim source As TextBox = TryCast(e.Source, TextBox)

    If source IsNot Nothing Then
        ' Change the TextBox color when it obtains focus.
        source.Background = Brushes.LightBlue

        ' Clear the TextBox.
        source.Clear()
    End If
End Sub

private void TextBoxLostKeyboardFocus(object sender, KeyboardFocusChangedEventArgs e)
{
    TextBox source = e.Source as TextBox;

    if (source != null)
    {
        // Change the TextBox color when it loses focus.
        source.Background = Brushes.White;

        // Set the  hit counter back to zero and updates the display.
        this.ResetCounter();
    }
}

Private Sub TextBoxLostKeyboardFocus(ByVal sender As Object, ByVal e As KeyboardFocusChangedEventArgs)
    Dim source As TextBox = TryCast(e.Source, TextBox)

    If source IsNot Nothing Then
        ' Change the TextBox color when it loses focus.
        source.Background = Brushes.White

        ' Set the  hit counter back to zero and updates the display.
        Me.ResetCounter()
    End If
End Sub

注解

这是一个附加事件。 WPF 将附加事件实现为路由事件。 附加事件本质上是一种 XAML 语言概念，用于引用可在未定义该事件的对象上处理的事件，WPF 通过允许事件遍历路由来扩展该事件。 附加事件在代码中没有直接处理语法;若要在代码中附加路由事件的处理程序，请使用指定的 Add*Handler 方法。 有关详细信息，请参阅 附加事件概述。

键盘焦点是指接收键盘输入的对象。 具有键盘焦点的 元素已 IsKeyboardFocused 设置为 true。 整个桌面上只能有一个具有键盘焦点的元素。 逻辑焦点是指具有焦点的焦点范围内的对象。 有关焦点、键盘焦点和逻辑焦点的详细信息，请参阅 输入概述 和 焦点概述。

PreviewGotKeyboardFocus如果处理了事件或PreviewLostKeyboardFocus事件，则键盘焦点不会更改。

路由事件信息
标识符字段 LostKeyboardFocusEvent
路由策略 鼓 泡
委托 KeyboardFocusChangedEventHandler

适用于