Keyboard.LostKeyboardFocus 附加事件
重要
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在元素丢失键盘焦点时发生。
C#
see AddLostKeyboardFocusHandler, and RemoveLostKeyboardFocusHandlersee AddLostKeyboardFocusHandler, and RemoveLostKeyboardFocusHandlersee AddLostKeyboardFocusHandler, and RemoveLostKeyboardFocusHandler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。
XML
<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>
C#
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
C#
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
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。
| 标识符字段 | LostKeyboardFocusEvent |
| 路由策略 | 鼓 泡 |
| 委托 | KeyboardFocusChangedEventHandler |
- 相应的隧道事件为 PreviewLostKeyboardFocus。
| 产品 | 版本 |
|---|---|
| .NET Framework | 3.0, 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1 |
| Windows Desktop | 3.0, 3.1, 5, 6, 7, 8, 9 |
