TriggerBase Class

Represents the base class for specifying a conditional value within a Style object.

Namespace:  System.Windows
Assembly:  PresentationFramework (in PresentationFramework.dll)

[LocalizabilityAttribute(LocalizationCategory.None, Readability = Readability.Unreadable)]
public abstract class TriggerBase : DependencyObject

The TriggerBase type exposes the following members.

  NameDescription
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.
Public propertyExitActionsGets a collection of TriggerAction objects to apply when the trigger object becomes inactive. This property does not apply to the EventTrigger class.
Public propertyIsSealedGets a value that indicates whether this instance is currently sealed (read-only). (Inherited from DependencyObject.)
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  NameDescription
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.)
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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The WPF styling and templating model allows you to specify triggers within your Style, ControlTemplate, and DataTemplate. Essentially, TriggerBase is the base class for objects that allow you to apply changes when certain conditions (such as when a certain property value becomes true, or when an event occurs) are satisfied.

There are several different types of triggers: Trigger, MultiTrigger, EventTrigger, DataTrigger, and MultiDataTrigger.

The Trigger class is the simplest type of triggers. A Trigger object allows you to apply changes based on the value of a property. For example, the following example shows a named Style available to Button controls. The Style defines a Trigger element that changes the Foreground property of a button when the IsPressed property is true.

<Style x:Key="Triggers" TargetType="Button">
    <Style.Triggers>
    <Trigger Property="IsPressed" Value="true">
        <Setter Property = "Foreground" Value="Green"/>
    </Trigger>
    </Style.Triggers>
</Style>

If you need to apply changes based on the state of multiple properties, you can use the MultiTrigger. For an example, see the MultiTrigger page.

The EventTrigger class allows you to apply changes when an event occurs. The following example contains two EventTrigger objects, one of which occurs when the mouse enters the element and the other occurs when the mouse leaves the element.

<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>

These are also the DataTrigger and the MultiDataTrigger classes. These are similar to Trigger and MultiTrigger except that they are for data-bound properties.

.NET Framework

Supported in: 4.5.2, 4.5.1, 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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