XAML - 触发器
基本上,触发器使您能够更改属性值或根据属性值采取行动。因此,它基本上允许您动态更改控件的外观和/或行为,而无需创建新控件。
触发器用于在满足某些条件时更改任何给定属性的值。触发器通常在样式中或文档的根目录中定义,并应用于该特定控件。有三种类型的触发器 −
- 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,它将立即或以动画方式更改另一个属性。例如,如果您想在鼠标悬停在按钮上时更改按钮的外观,则可以使用属性触发器。
示例
以下示例演示了如何在鼠标进入按钮区域时更改按钮的前景色。
<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>
编译并执行上述代码时,将产生以下输出 −

当鼠标进入按钮区域时,前景色将变为绿色。

数据触发器
当绑定数据满足某些条件时,数据触发器会执行某些操作。让我们看一下以下 XAML 代码,其中使用一些属性创建了一个复选框和一个文本块。选中复选框后,它会将前景色更改为红色。
<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>
编译并执行上述代码时,将产生以下输出 −

选中复选框后,文本块的前景色将变为红色。

事件触发器
事件触发器在触发特定事件时执行某些操作。它通常用于完成一些动画,如 DoubleAnimation、ColorAnimation 等。以下代码块创建了一个简单的按钮。当触发单击事件时,它将扩展按钮的宽度和高度。
<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>
当您编译并执行上述代码时,它将产生以下输出 −

现在,单击按钮,您将观察到它将开始在两个维度上扩展。
