如何给出EventTrigger的条件？

Question

可以在EventTrigger中给出条件吗？我为Radio按钮编写了一个以下EventTrigger(Mouse.MouseLeave).我希望不应该触发处于Checked条件(IsChecked = True)的项目.

<EventTrigger RoutedEvent="Mouse.MouseLeave" SourceName="border">                                 
      <BeginStoryboard Name="out_BeginStoryboard" Storyboard="{StaticResource out}" />
      <RemoveStoryboard BeginStoryboardName="over_BeginStoryboard" />
</EventTrigger>

请让我知道如何实现这一目标？

提前致谢.

Answer 1

您不能以这种方式使用EventTrigger.调用EventTriggers的WPF的RoutedEventHandler没有提供任何使触发器成为条件的机制,并且你无法通过继承TriggerAction来解决这个问题,因为没有受保护的Invoke()或Execute()操作要覆盖.

但是,使用自定义类可以非常轻松地完成此操作.以下是它的使用方法:

<Border>
  <my:ConditionalEventTrigger.Triggers>
    <my:ConditionalEventTriggerCollection>
      <my:ConditionalEventTrigger RoutedEvent="Mouse.MouseLeave"
                                  Condition="{Binding IsChecked, ElementName=checkbox}">
        <BeginStoryboard Name="out_BeginStoryboard" Storyboard="{StaticResource out}" />               
        <RemoveStoryboard BeginStoryboardName="over_BeginStoryboard" />               
      </my:ConditionalEventTrigger>               
    </my:ConditionalEventTriggerCollection>
  </my:ConditionalEventTrigger.Triggers>
  ...

以下是它的实现方式:

[ContentProperty("Actions")] 
public class ConditionalEventTrigger : FrameworkContentElement
{ 
  public RoutedEvent RoutedEvent { get; set; } 
  public List<TriggerAction> Actions { get; set; }

  // Condition
  public bool Condition { get { return (bool)GetValue(ConditionProperty); } set { SetValue(ConditionProperty, value); } }
  public static readonly DependencyProperty ConditionProperty = DependencyProperty.Register("Condition", typeof(bool), typeof(ConditionalEventTrigger));

  // "Triggers" attached property
  public static ConditionalEventTriggerCollection GetTriggers(DependencyObject obj) { return (ConditionalEventTriggerCollection)obj.GetValue(TriggersProperty); }
  public static void SetTriggers(DependencyObject obj, ConditionalEventTriggerCollection value) { obj.SetValue(TriggersProperty, value); }
  public static readonly DependencyProperty TriggersProperty = DependencyProperty.RegisterAttached("Triggers", typeof(ConditionalEventTriggerCollection), typeof(ConditionalEventTrigger), new PropertyMetadata 
  { 
    PropertyChangedCallback = (obj, e) => 
    { 
      // When "Triggers" is set, register handlers for each trigger in the list 
      var element = (FrameworkElement)obj; 
      var triggers = (List<ConditionalEventTrigger>)e.NewValue;
      foreach(var trigger in triggers)
        element.AddHandler(trigger.RoutedEvent, new RoutedEventHandler((obj2, e2) =>
          trigger.OnRoutedEvent(element)));
    } 
  });

  public ConditionalEventTrigger()
  {
    Actions = new List<TriggerAction>();
  }

  // When an event fires, check the condition and if it is true fire the actions 
  void OnRoutedEvent(FrameworkElement element) 
  { 
    DataContext = element.DataContext;  // Allow data binding to access element properties
    if(Condition) 
    { 
      // Construct an EventTrigger containing the actions, then trigger it 
      var dummyTrigger = new EventTrigger { RoutedEvent = _triggerActionsEvent }; 
      foreach(var action in Actions) 
        dummyTrigger.Actions.Add(action); 

      element.Triggers.Add(dummyTrigger); 
      try 
      { 
        element.RaiseEvent(new RoutedEventArgs(_triggerActionsEvent)); 
      } 
      finally 
      { 
        element.Triggers.Remove(dummyTrigger); 
      } 
    } 
  } 

  static RoutedEvent _triggerActionsEvent = EventManager.RegisterRoutedEvent("", RoutingStrategy.Direct, typeof(EventHandler), typeof(ConditionalEventTrigger)); 

} 

// Create collection type visible to XAML - since it is attached we cannot construct it in code 
public class ConditionalEventTriggerCollection : List<ConditionalEventTrigger> {} 

请享用!

Answer 2

这对我有用...

我想基于将鼠标悬停在UI元素上并且UI元素的相关所有者处于活动状态(即启用以使玩家移动)来执行动画.

为了支持这些要求,我使用相对源绑定来克服对事件触发条件的不足支持.

例:

<MultiDataTrigger>
    <MultiDataTrigger.Conditions>
        <Condition Binding="{Binding RelativeSource={RelativeSource self}, Path=IsMouseOver}" Value="True" />
        <Condition Binding="{Binding Path=IsPlayer1Active}" Value="True" />
    </MultiDataTrigger.Conditions>
    <MultiDataTrigger.EnterActions>
        <BeginStoryboard>
            <Storyboard>
                <ColorAnimation Storyboard.TargetProperty="Background.GradientStops[0].Color" To="#FF585454" Duration="0:0:.25"/>
                <ColorAnimation Storyboard.TargetProperty="Background.GradientStops[1].Color" To="Black" Duration="0:0:2"/>
            </Storyboard>
        </BeginStoryboard>
    </MultiDataTrigger.EnterActions>
</MultiDataTrigger>

Answer 3

在你的情况下，你需要：

<EventTrigger RoutedEvent="Checked" SourceName="border">

编辑：根据您的评论，您正在寻找多数据触发器。

   <MultiDataTrigger>
        <MultiDataTrigger.Conditions>
            <Condition SourceName="border" Property="IsMouseOver" Value="false" />                                            
        </MultiDataTrigger.Conditions>
        <MultiDataTrigger.EnterActions>
            <BeginStoryboard Name="out_BeginStoryboard" Storyboard="{StaticResource out}" />
            <RemoveStoryboard BeginStoryboardName="over_BeginStoryboard" />
        </MultiDataTrigger.EnterActions>
   </MultiDataTrigger>