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Trigger, classe

Represents a trigger that applies property values or performs actions conditionally.

Espace de noms: System.Windows
Assembly : PresentationFramework (dans presentationframework.dll)
Espace de noms XML :  http://schemas.microsoft.com/winfx/2006/xaml/presentation

[ContentPropertyAttribute("Setters")] 
public class Trigger : TriggerBase, IAddChild
/** @attribute ContentPropertyAttribute("Setters") */ 
public class Trigger extends TriggerBase implements IAddChild
ContentPropertyAttribute("Setters") 
public class Trigger extends TriggerBase implements IAddChild
<Trigger>
  Setters
</Trigger>

WPF defines properties that correspond to end-user actions, such as the IsMouseOver property that is set to true when the user hovers the cursor over a UIElement or the corresponding IsMouseOver property of a ContentElement. Representing end-user actions in property values, along with the Trigger element, allows WPF styles to change property values based on those end-user actions, all from within markup.

The properties changed by triggers are automatically reset to their previous value when the triggered condition is no longer satisfied. Triggers are optimized for transient states which are expected to change and return to original state, such as IsPressed on Button and IsSelected on ListBoxItem. The Property of interest must be a dependency property.

Note that you must specify both the Property and Value properties on a Trigger for the trigger to be meaningful. If one or both of the properties are not set, an exception is thrown.

The Setters property of a Trigger object can only consist of Setter objects. Adding a Setter child to a Trigger object implicitly adds it to the SetterBaseCollection for the Trigger object. EventSetter objects are not supported; only Style.Setters supports EventSetter objects.

There are other types of triggers. MultiTrigger allows you to apply changes based on the state of multiple properties. EventTrigger allows you to apply changes when an event occurs. DataTrigger and MultiTrigger are for data-bound properties.

The following example contains two triggers. The first changes the Background property of a Button when the IsMouseOver property is true. The second changes the Foreground property of a button when the IsPressed property is true.

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

Davantage de code

How to: Trigger an Animation When a Property Value Changes

This example shows how to use a Trigger to start a Storyboard when a property value changes. You can use a Trigger inside a Style, ControlTemplate, or DataTemplate.

Les membres statiques publics (Shared en Visual Basic) de ce type sont thread-safe. Il n'est pas garanti que les membres d'instance soient thread-safe.

Microsoft .NET Framework 3.0 est pris en charge sur Windows Vista, Microsoft Windows XP SP2 et Windows Server 2003 SP1.

.NET Framework

Prise en charge dans : 3.0

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