一、属性触发器
要改变的属性值不能再控件里面设置初始值，否则不能触发，如下例的Width

     <Rectangle Height="100"  Fill="Black"  Name="R1" RenderTransformOrigin="0.5,0.5">
            <Rectangle.RenderTransform>
                <RotateTransform></RotateTransform>
            </Rectangle.RenderTransform>
            <Rectangle.Style>
                <Style TargetType="Rectangle">
                    <Setter Property="Width" Value="100"></Setter>
                    <Style.Triggers>
                        <Trigger Property="Fill" Value="Black">
                            <Trigger.EnterActions>
                                <BeginStoryboard>
                                    <Storyboard RepeatBehavior="Forever" >
                                        <DoubleAnimation Storyboard.TargetProperty="Height" From="100" To="200" Duration="0:0:1"></DoubleAnimation>
                                        <DoubleAnimation Storyboard.TargetProperty="(Rectangle.RenderTransform).(RotateTransform.Angle)" From="0" To="360" Duration="0:0:1"></DoubleAnimation>
                                    </Storyboard>
                                </BeginStoryboard>
                            </Trigger.EnterActions>
                            <Setter Property="Width" Value="200"></Setter>
                        </Trigger>
                    </Style.Triggers>
                </Style>
            </Rectangle.Style>
        </Rectangle>

二、数据触发器
相比对属性触发器而言，他可以绑定其他控件的属性或者ViewModel里面的属性

        <Rectangle  Width="200" Name="R2" Fill="Green" RenderTransformOrigin="0.5,0.5">
            <Rectangle.RenderTransform >
                <RotateTransform x:Name="R2RT" Angle="0"></RotateTransform>
            </Rectangle.RenderTransform>
            <Rectangle.Style>
                <Style TargetType="Rectangle">
                    <Setter Property="Height" Value="100"></Setter>
                    <Style.Triggers>
                        <DataTrigger Binding="{Binding ElementName=R1,Path=Fill}" Value="Black">
                            <Setter Property="Height" Value="200"></Setter>
                            <DataTrigger.EnterActions>
                                <BeginStoryboard>
                                    <Storyboard RepeatBehavior="Forever" >
                                        <DoubleAnimation Storyboard.TargetProperty="(Rectangle.RenderTransform).(RotateTransform.Angle)" From="0" To="360" Duration="0:0:1"></DoubleAnimation>
                                    </Storyboard>
                                </BeginStoryboard>
                            </DataTrigger.EnterActions>
                        </DataTrigger>
                    </Style.Triggers>
                </Style>
            </Rectangle.Style>

        </Rectangle>

三、事件触发器

1. 只能触发故事板（不知道是否正确）
2. 分为控件触发器和样式触发器（这两个名字自己取的，也不知道有没有官方说法）
   控件触发器( Storyboard.TargetName似乎专为它服务)

     <Rectangle Width="200" Height="200" Name="R3" RenderTransformOrigin="0.5,0.5" Fill="Yellow">
            <Rectangle.RenderTransform>
                <RotateTransform x:Name="R3RT"></RotateTransform>
            </Rectangle.RenderTransform>
            
            <Rectangle.Triggers>
                <EventTrigger RoutedEvent="Mouse.MouseEnter">
                    <BeginStoryboard>
                        <Storyboard>
                            <DoubleAnimation Storyboard.TargetName="R2RT" Storyboard.TargetProperty="Angle" From="0" To="360" RepeatBehavior="Forever" Duration="0:0:1"></DoubleAnimation>
                            <DoubleAnimation Storyboard.TargetName="R3RT" Storyboard.TargetProperty="Angle" From="0" To="360" RepeatBehavior="Forever" Duration="0:0:1"></DoubleAnimation>
                        </Storyboard>
                    </BeginStoryboard>
                </EventTrigger>
            </Rectangle.Triggers>
        </Rectangle>

样式触发器

        <Rectangle Width="200" Height="200" Name="R4" RenderTransformOrigin="0.5,0.5" Fill="Yellow">
            <Rectangle.RenderTransform>
                <RotateTransform x:Name="R4RT"></RotateTransform>
            </Rectangle.RenderTransform>
            <Rectangle.Style>
                <Style TargetType="Rectangle">
                    <Style.Triggers>
                        <EventTrigger RoutedEvent="Mouse.MouseEnter">
                            <EventTrigger.Actions>
                                <BeginStoryboard>
                                    <Storyboard>
                                        <DoubleAnimation Storyboard.TargetProperty="(Rectangle.RenderTransform).(RotateTransform.Angle)" From="0" To="360" RepeatBehavior="Forever" Duration="0:0:1"></DoubleAnimation>
                                    </Storyboard>
                                </BeginStoryboard>
                            </EventTrigger.Actions>
                        </EventTrigger>
                    </Style.Triggers>
                </Style>
            </Rectangle.Style>
        </Rectangle>

[WPF 学习] 10.触发器