WPF - 触发器

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触发器基本上使您能够根据属性的值更改属性值或执行操作。因此，它允许您动态更改控件的外观和/或行为，而无需创建新的控件。

触发器用于在满足某些条件时更改任何给定属性的值。触发器通常定义在样式中或文档的根目录中，这些样式应用于该特定控件。触发器有三种类型：

• 属性触发器
• 数据触发器
• 事件触发器

属性触发器

在属性触发器中，当一个属性发生变化时，它将导致另一个属性立即或动画变化。例如，您可以使用属性触发器在鼠标悬停在按钮上时更改按钮的外观。

以下示例代码演示了如何在鼠标悬停在按钮上时更改按钮的前景色。

<Window x:Class = "WPFPropertyTriggers.MainWindow" 
   xmlns = "http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
   xmlns:x = "http://schemas.microsoft.com/winfx/2006/xaml" 
   Title = "MainWindow" Height = "350" Width = "604"> 
	
   <Window.Resources> 
      <Style x:Key = "TriggerStyle" TargetType = "Button"> 
         <Setter Property = "Foreground" Value = "Blue" /> 
         <Style.Triggers> 
            <Trigger Property = "IsMouseOver" Value = "True"> 
               <Setter Property = "Foreground" Value = "Green" /> 
            </Trigger> 
         </Style.Triggers> 
      </Style> 
   </Window.Resources> 
	
   <Grid> 
      <Button Width = "100" Height = "70"
         Style = "{StaticResource TriggerStyle}" Content = "Trigger"/> 
   </Grid> 
	
</Window> 

编译并执行上述代码后，将生成以下窗口：

当鼠标悬停在按钮上时，其前景色将更改为绿色。

数据触发器

数据触发器在绑定数据满足某些条件时执行某些操作。让我们看一下以下 XAML 代码，其中创建了一个复选框和一个文本块，并带有一些属性。当选中复选框时，它将将其前景色更改为红色。

<Window x:Class = "WPFDataTrigger.MainWindow" 
   xmlns = "http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
   xmlns:x = "http://schemas.microsoft.com/winfx/2006/xaml" 
   Title = "Data Trigger" Height = "350" Width = "604">
	
   <StackPanel HorizontalAlignment = "Center"> 
      <CheckBox x:Name = "redColorCheckBox" 
         Content = "Set red as foreground color" Margin = "20"/> 
			
      <TextBlock Name = "txtblock" VerticalAlignment = "Center" 
         Text = "Event Trigger" FontSize = "24" Margin = "20"> 
         <TextBlock.Style> 
            <Style> 
               <Style.Triggers> 
                  <DataTrigger Binding = "{Binding ElementName = redColorCheckBox, Path = IsChecked}" 
                     Value = "true"> 
                     <Setter Property = "TextBlock.Foreground" Value = "Red"/> 
                     <Setter Property = "TextBlock.Cursor" Value = "Hand" /> 
                  </DataTrigger> 
               </Style.Triggers> 
            </Style> 
         </TextBlock.Style> 
      </TextBlock> 
		
   </StackPanel> 
	
</Window>

编译并执行上述代码后，将生成以下输出：

选中复选框后，文本块将将其前景色更改为红色。

事件触发器

事件触发器在触发特定事件时执行某些操作。它通常用于在控件上实现一些动画，例如 DoubleAnumatio、ColorAnimation 等。在以下示例中，我们将创建一个简单的按钮。当单击事件触发时，它将扩展按钮的宽度和高度。

<Window x:Class = "WPFEventTrigger.MainWindow"
   xmlns = "http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
   xmlns:x = "http://schemas.microsoft.com/winfx/2006/xaml" 
   Title = "MainWindow" Height = "350" Width = "604"> 
	
   <Grid> 
      <Button Content = "Click Me" Width = "60" Height = "30">
		
         <Button.Triggers> 
            <EventTrigger RoutedEvent = "Button.Click"> 
               <EventTrigger.Actions> 
                  <BeginStoryboard> 
                     <Storyboard> 
							
                        <DoubleAnimationUsingKeyFrames Storyboard.TargetProperty = 
                           "Width" Duration = "0:0:4"> 
                           <LinearDoubleKeyFrame Value = "60" KeyTime = "0:0:0"/> 
                           <LinearDoubleKeyFrame Value = "120" KeyTime = "0:0:1"/> 
                           <LinearDoubleKeyFrame Value = "200" KeyTime = "0:0:2"/> 
                           <LinearDoubleKeyFrame Value = "300" KeyTime = "0:0:3"/> 
                        </DoubleAnimationUsingKeyFrames>
								
                        <DoubleAnimationUsingKeyFrames Storyboard.TargetProperty = "Height" 
                           Duration = "0:0:4"> 
                           <LinearDoubleKeyFrame Value = "30" KeyTime = "0:0:0"/> 
                           <LinearDoubleKeyFrame Value = "40" KeyTime = "0:0:1"/> 
                           <LinearDoubleKeyFrame Value = "80" KeyTime = "0:0:2"/> 
                           <LinearDoubleKeyFrame Value = "150" KeyTime = "0:0:3"/> 
                        </DoubleAnimationUsingKeyFrames>
								
                     </Storyboard> 
                  </BeginStoryboard> 
               </EventTrigger.Actions> 
            </EventTrigger> 
         </Button.Triggers> 
			
      </Button> 
   </Grid> 
	
</Window>

编译并执行上述代码后，将生成以下窗口：

单击按钮后，您将观察到它将开始在两个维度上扩展。

我们建议您编译并执行上述示例，并将触发器应用于其他属性。