WPF中有种叫做触发器的东西（记住不是数据库的trigger哦）。它的主要作用是根据trigger的不同条件来自动更改外观属性，或者执行动画等操作。
WPFtrigger的主要类型有：Trigger、MultiTrigger、DataTrigger、MultiDataTrigger、EventTrigger几种。从字面意思上我们想大家已经知道个大概，接下来我将还会用实例代码逐一进行介绍。trigger主要运用的场景在Style、ControlTemplate、DataTemplate三个地方。在这些地方可以使用trigger，具体视情况而定。
1.在Style中使用各种trigger
在style中使用的trigger主要是属性的触发器，当属性的值发生改变是将会引发触发器。
a.普通属性trigger 当鼠标滑过时字体变成红色
<span> </span><CheckBox Content="Style Trigger MouseOver Red">
<CheckBox.Resources>
<Style TargetType="{x:Type CheckBox}">
<Setter Property="Foreground" Value="SkyBlue"/>
<Style.Triggers>
<!--鼠标滑过时字体为红色-->
<Trigger Property="IsMouseOver" Value="True">
<Setter Property="Foreground" Value="Red"/>
</Trigger>
</Style.Triggers>
</Style>
</CheckBox.Resources>
</CheckBox>
b.普通属性MultiTrigger 当checkbox勾选并且鼠标滑过时字体变成绿色
<span> </span><CheckBox Content="Style MultiTrigger Checked and MouseOver Green ">
<CheckBox.Resources>
<Style TargetType="{x:Type CheckBox}">
<Setter Property="Foreground" Value="SkyBlue"/>
<Style.Triggers>
<MultiTrigger>
<MultiTrigger.Conditions>
<Condition Property="IsChecked" Value="True" />
<Condition Property="IsMouseOver" Value="True" />
</MultiTrigger.Conditions>
<Setter Property="Foreground" Value="Green"/>
</MultiTrigger>
</Style.Triggers>
</Style>
</CheckBox.Resources>
</CheckBox>
c.EventTrigger 鼠标划入长度变长 鼠标移出 长度变短
<CheckBox Content="Style EventTrigger " Width="" HorizontalAlignment="Left">
<CheckBox.Resources>
<Style TargetType="{x:Type CheckBox}">
<Setter Property="Foreground" Value="SkyBlue"/>
<Style.Triggers>
<EventTrigger RoutedEvent="Mouse.MouseEnter">
<EventTrigger.Actions>
<BeginStoryboard>
<Storyboard>
<DoubleAnimation
Duration="0:0:0.2"
Storyboard.TargetProperty="Width"
To="" />
</Storyboard>
</BeginStoryboard>
</EventTrigger.Actions>
</EventTrigger>
<EventTrigger RoutedEvent="Mouse.MouseLeave">
<EventTrigger.Actions>
<BeginStoryboard>
<Storyboard>
<DoubleAnimation
Duration="0:0:0.2"
Storyboard.TargetProperty="Width"
To="" />
</Storyboard>
</BeginStoryboard>
</EventTrigger.Actions>
</EventTrigger>
</Style.Triggers>
</Style>
</CheckBox.Resources>
</CheckBox>
2.在ControlTemplate中使用trigger
在ControlTemplate中使用的trigger主要是在controltemplate中的元素的触发器，当属性的值发生改变是将会引发触发器。
属性为“Border” 的鼠标滑过时背景变色，其他的trigger同上面的style一样 这里就不多举例了
<Button Content="ControlTemplate" Width="" Height="">
<Button.Resources>
<Style TargetType="{x:Type Button}">
<Setter Property="Background" Value="Gray"/>
<Setter Property="BorderBrush" Value="Black"/>
<Setter Property="Cursor" Value="Hand"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type Button}">
<StackPanel>
<Border Height="" Background="Red"></Border>
<Border x:Name="Border" CornerRadius="" BorderThickness="" Background="{TemplateBinding Background}" BorderBrush="{TemplateBinding BorderBrush}">
<ContentPresenter VerticalAlignment="Center" HorizontalAlignment="Center"/>
</Border>
</StackPanel> <ControlTemplate.Triggers>
<Trigger Property="IsMouseOver" Value="True">
<Setter TargetName="Border" Property="Background" Value="#FFC2E0FF"/>
<Setter TargetName="Border" Property="BorderBrush" Value="#FF3399FF"/>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</Button.Resources>
</Button>
3.在DataTemplate中使用trigger
在DataTemplate中使用trigger可以根据绑定的数据不同显示不同的内容。
<TreeView Name="_tree" Margin="" BorderThickness="" VerticalAlignment="Stretch" Background="Transparent" ItemsSource="{Binding Children}" >
<TreeView.ItemTemplate>
<HierarchicalDataTemplate ItemsSource="{Binding Children}">
<Border CornerRadius="" Margin="" x:Name="back" MinWidth=""
Background="Transparent" DataContext="{Binding}" PreviewMouseMove="TreeItem_PreviewMouseMove">
<StackPanel Orientation="Horizontal" Margin="">
<Image x:Name="BGimage" Source="/Vdc3D.Coms.DModelEditor;component/Images/item.png" Height="" Width="" />
<TextBlock Text="{Binding ShowText}" Margin="2 0"/>
</StackPanel>
<Border.ContextMenu>
<ContextMenu x:Name="menu" >
<MenuItem Header="Add Directory" x:Name="menu_addDir" Click="AddDir_Click" DataContext="{Binding}"/>
<MenuItem Header="Add Property" x:Name="menu_addChild" Click="AddChild_Click" DataContext="{Binding}"/>
<MenuItem Header="Edit" Click="Modify_Click" DataContext="{Binding}"/>
<MenuItem Header="Delete" Click="Delete_Click" DataContext="{Binding}"/>
</ContextMenu>
</Border.ContextMenu>
</Border>
<HierarchicalDataTemplate.Triggers>
<MultiDataTrigger>
<MultiDataTrigger.Conditions>
<Condition Binding="{Binding RelativeSource={RelativeSource Mode=FindAncestor,AncestorType={x:Type TreeViewItem}},Path=IsExpanded}" Value="False"/>
<Condition Binding="{Binding IsDir}" Value="True"/>
</MultiDataTrigger.Conditions>
<MultiDataTrigger.Setters>
<Setter TargetName="BGimage" Property="Source" Value="/Vdc3D.Coms.DModelEditor;component/Images/dir.png" />
</MultiDataTrigger.Setters>
</MultiDataTrigger>
<MultiDataTrigger>
<MultiDataTrigger.Conditions>
<Condition Binding="{Binding RelativeSource={RelativeSource Mode=FindAncestor,AncestorType={x:Type TreeViewItem}},Path=IsExpanded}" Value="True"/>
<Condition Binding="{Binding IsDir}" Value="True"/>
</MultiDataTrigger.Conditions>
<MultiDataTrigger.Setters>
<Setter TargetName="BGimage" Property="Source" Value="/Vdc3D.Coms.DModelEditor;component/Images/dir_open.png" />
</MultiDataTrigger.Setters>
</MultiDataTrigger>
<DataTrigger Binding="{Binding IsDir}" Value="True">
<Setter TargetName="menu_addDir" Property="Visibility" Value="Visible"/>
<Setter TargetName="menu_addChild" Property="Visibility" Value="Visible"/>
</DataTrigger>
<DataTrigger Binding="{Binding IsDir}" Value="False">
<Setter TargetName="menu_addDir" Property="Visibility" Value="Collapsed"/>
<Setter TargetName="menu_addChild" Property="Visibility" Value="Collapsed"/>
</DataTrigger>
</HierarchicalDataTemplate.Triggers>
</HierarchicalDataTemplate>
</TreeView.ItemTemplate>
</TreeView>
这是一个treeview控件 根据绑定的isdir值不同 可以显示icon是一个目录（文件夹）或者是一个文件，看是不是很简单呢
以上只是简单的介绍了trigger的一些用法，具体的功能大家可以自由发挥，这也是wpf的强大之处
