EventTrigger Class

Represents a trigger that applies a set of actions in response to an event.

Namespace:  System.Windows
Assembly:  PresentationFramework (in PresentationFramework.dll)
XMLNS for XAML: http://schemas.microsoft.com/winfx/2006/xaml/presentation, http://schemas.microsoft.com/netfx/2007/xaml/presentation

[<ContentPropertyAttribute("Actions")>]
type EventTrigger =  
    class 
        inherit TriggerBase 
        interface IAddChild 
    end
<EventTrigger>
  Actions
</EventTrigger>

The EventTrigger type exposes the following members.

  NameDescription
Public methodEventTrigger()Initializes a new instance of the EventTrigger class.
Public methodEventTrigger(RoutedEvent)Initializes a new instance of the EventTrigger class with the specified event.
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  NameDescription
Public propertyActionsGets the collection of actions to apply when the event occurs.
Public propertyDependencyObjectTypeGets the DependencyObjectType that wraps the CLR type of this instance.  (Inherited from DependencyObject.)
Public propertyDispatcherGets the Dispatcher this DispatcherObject is associated with. (Inherited from DispatcherObject.)
Public propertyEnterActionsGets a collection of TriggerAction objects to apply when the trigger object becomes active. This property does not apply to the EventTrigger class. (Inherited from TriggerBase.)
Public propertyExitActionsGets a collection of TriggerAction objects to apply when the trigger object becomes inactive. This property does not apply to the EventTrigger class. (Inherited from TriggerBase.)
Public propertyIsSealedGets a value that indicates whether this instance is currently sealed (read-only). (Inherited from DependencyObject.)
Public propertyRoutedEventGets or sets the RoutedEvent that will activate this trigger.
Public propertySourceNameGets or sets the name of the object with the event that activates this trigger. This is only used by element triggers or template triggers.
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  NameDescription
Protected methodAddChildAdds the specified object to the Actions collection of the current event trigger.
Protected methodAddTextThis method is not supported and results in an exception.
Public methodCheckAccessDetermines whether the calling thread has access to this DispatcherObject. (Inherited from DispatcherObject.)
Public methodClearValue(DependencyProperty)Clears the local value of a property. The property to be cleared is specified by a DependencyProperty identifier. (Inherited from DependencyObject.)
Public methodClearValue(DependencyPropertyKey)Clears the local value of a read-only property. The property to be cleared is specified by a DependencyPropertyKey. (Inherited from DependencyObject.)
Public methodCoerceValueCoerces the value of the specified dependency property. This is accomplished by invoking any CoerceValueCallback function specified in property metadata for the dependency property as it exists on the calling DependencyObject. (Inherited from DependencyObject.)
Public methodEqualsDetermines whether a provided DependencyObject is equivalent to the current DependencyObject. (Inherited from DependencyObject.)
Protected methodFinalizeAllows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Public methodGetHashCodeGets a hash code for this DependencyObject. (Inherited from DependencyObject.)
Public methodGetLocalValueEnumeratorCreates a specialized enumerator for determining which dependency properties have locally set values on this DependencyObject. (Inherited from DependencyObject.)
Public methodGetTypeGets the Type of the current instance. (Inherited from Object.)
Public methodGetValueReturns the current effective value of a dependency property on this instance of a DependencyObject. (Inherited from DependencyObject.)
Public methodInvalidatePropertyRe-evaluates the effective value for the specified dependency property (Inherited from DependencyObject.)
Protected methodMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Protected methodOnPropertyChangedInvoked whenever the effective value of any dependency property on this DependencyObject has been updated. The specific dependency property that changed is reported in the event data. (Inherited from DependencyObject.)
Public methodReadLocalValueReturns the local value of a dependency property, if it exists. (Inherited from DependencyObject.)
Public methodSetCurrentValueSets the value of a dependency property without changing its value source. (Inherited from DependencyObject.)
Public methodSetValue(DependencyProperty, Object)Sets the local value of a dependency property, specified by its dependency property identifier. (Inherited from DependencyObject.)
Public methodSetValue(DependencyPropertyKey, Object)Sets the local value of a read-only dependency property, specified by the DependencyPropertyKey identifier of the dependency property. (Inherited from DependencyObject.)
Public methodShouldSerializeActionsReturns whether serialization processes should serialize the effective value of the Actions property on instances of this class.
Protected methodShouldSerializePropertyReturns a value that indicates whether serialization processes should serialize the value for the provided dependency property. (Inherited from DependencyObject.)
Public methodToStringReturns a string that represents the current object. (Inherited from Object.)
Public methodVerifyAccessEnforces that the calling thread has access to this DispatcherObject. (Inherited from DispatcherObject.)
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  NameDescription
Explicit interface implemetationPrivate methodIAddChild.AddChildInfrastructure. Adds a child object.
Explicit interface implemetationPrivate methodIAddChild.AddTextInfrastructure. Adds the text content of a node to the object.
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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>

More Code

How to: Use Event Triggers to Control a Storyboard After It StartsThis example shows how to control a Storyboard after it starts. To start a Storyboard by using XAML, use BeginStoryboard, which distributes the animations to the objects and properties they animate and then starts the storyboard. If you give BeginStoryboard a name by specifying its Name property, you make it a controllable storyboard. You can then interactively control the storyboard after it starts.

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.
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