Trigger objects have the Setters, EnterActions, and ExitActions properties that apply changes or actions based on the state of certain properties, while EventTrigger objects start a set of Actions when a specified routed event occurs. For example, you may want to use an EventTrigger to start a set of animations when the mouse pointer is over a certain user interface (UI) control. Unlike Trigger, EventTrigger has no concept of termination of state, so the action will not be undone once the condition that raised the event is no longer true.

Note that when using an EventTrigger, you need to choose events that do not interfere with the inherent behavior of your control. Controls such as Button or TextBox perform specific actions on user input events such as mouse clicks and keyboard events. For example, if you are styling a button and try to set the MouseDown event as the RoutedEvent of an EventTrigger, the EventTrigger never gets applied because the event first gets handled by the button. Instead, you can use the PreviewMouseDown event or a different event.

When using data binding, if you are using the TargetUpdated event, you must set the NotifyOnTargetUpdated value of your Binding object to true for the event to be raised.

Adding a TriggerAction child to an EventTrigger object implicitly adds it to the TriggerActionCollection for the EventTrigger object.

This example shows how to use event triggers in a style to animate the MouseEnter and MouseLeave events of a FrameworkElement. In this example, the Style has the TargetType set to Rectangle. Therefore, there is no need to qualify the MouseEnter and MouseLeave event names with the class name.

<Style TargetType="Rectangle">
  <Setter Property="Width" Value="50" />
  <Setter Property="Height" Value="50" />
  <Setter Property="Margin" Value="20" />
  <Setter Property="HorizontalAlignment" Value="Left" />
  <Style.Triggers>
    <EventTrigger RoutedEvent="MouseEnter">
        <BeginStoryboard>
            <Storyboard>
              <DoubleAnimation To="300" Duration="0:0:1.5" 
                AccelerationRatio="0.10" DecelerationRatio="0.25" 
                Storyboard.TargetProperty="(Canvas.Width)" />
            </Storyboard>
        </BeginStoryboard>
    </EventTrigger>
    <EventTrigger RoutedEvent="MouseLeave">
        <BeginStoryboard>
            <Storyboard>
              <DoubleAnimation Duration="0:0:1.5" 
                AccelerationRatio="0.10" DecelerationRatio="0.25" 
                Storyboard.TargetProperty="(Canvas.Width)" />
            </Storyboard>
        </BeginStoryboard>
    </EventTrigger>
  </Style.Triggers>
</Style>

To see the complete sample, see Event Triggers Sample.

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.NET Framework

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