XAML - 觸發器

基本上，觸發器使您能夠根據屬性的值更改屬性值或執行操作。因此，它基本上允許您動態更改控制元件的外觀和/或行為，而無需建立新的控制元件。

觸發器用於在滿足某些條件時更改任何給定屬性的值。觸發器通常在樣式或文件的根目錄中定義，並應用於該特定控制元件。觸發器有三種類型：

屬性觸發器
資料觸發器
事件觸發器

屬性觸發器

在屬性觸發器中，當一個屬性發生變化時，它將導致另一個屬性發生立即或動畫變化。例如，如果要在滑鼠懸停在按鈕上時更改按鈕外觀，可以使用屬性觸發器。

示例

以下示例演示瞭如何在滑鼠進入其區域時更改按鈕的前景色。

<Window x:Class = "XAMLPropertyTriggers.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>

編譯並執行上述程式碼後，將生成以下輸出：

當滑鼠進入按鈕區域時，前景色將更改為綠色。

資料觸發器

資料觸發器在繫結資料滿足某些條件時執行某些操作。讓我們看一下以下 XAML 程式碼，其中建立了一個複選框和一個文字塊，並具有一些屬性。當選中複選框時，它會將前景色更改為紅色。

<Window x:Class = "XAMLDataTrigger.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>

編譯並執行上述程式碼後，將生成以下輸出：

選中複選框後，文字塊的前景色將更改為紅色。

事件觸發器

事件觸發器在觸發特定事件時執行某些操作。它通常用於完成一些動畫，例如 DoubleAnimation、ColorAnimation 等。以下程式碼塊建立了一個簡單的按鈕。當單擊事件觸發時，它將擴充套件按鈕的寬度和高度。

<Window x:Class = "XAMLEventTrigger.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>

編譯並執行上述程式碼後，將生成以下輸出：

現在，單擊按鈕，您將觀察到它將開始在兩個維度上擴充套件。

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