SL4/MVVM:在 VM 中使用 void Foo() 处理 MouseDragElementBehavior.Dragging 事件 [英] SL4/MVVM: Handle MouseDragElementBehavior.Dragging event with void Foo() in VM

问题描述

我正在尝试处理我拥有的控件上的 MouseDragElementBehavior.Dragging 事件.见 在这里了解我为什么要这样做的背景.

I am trying to handle the MouseDragElementBehavior.Dragging event on a control I have. See here for background on why I want to do this.

我无法连接此事件.从 XAML 中您可以看到我向用户控件添加了一个行为.然后我尝试通过 CallMethodAction EventTrigger 在行为上的 Dragging 事件中添加一个处理程序.

I am having trouble wiring up this event. From the XAML you can see I have added a behavior to the user control. Then I attempted to add a handler to the Dragging event on the behavior via the CallMethodAction EventTrigger.

<i:Interaction.Behaviors>
    <ei:MouseDragElementBehavior ConstrainToParentBounds="True">
        <i:Interaction.Triggers>
            <i:EventTrigger EventName="Dragging">
                <ei:CallMethodAction MethodName="NotifyChildrenYouAreDragging" TargetObject="{Binding}"/>
            </i:EventTrigger>
        </i:Interaction.Triggers>
    </ei:MouseDragElementBehavior>
</i:Interaction.Behaviors>

我尝试了以下方法签名但没有成功:

I have tried the following method signatures with no luck:

void NotifyChildrenYouAreDragging(){}
void NotifyChildrenYouAreDragging(object sender, EventArgs e){}
void NotifyChildrenYouAreDragging(object sender, MouseEventArgs e){}

有人有使用触发器来处理附加行为中的事件的经验吗?

Anyone have experience using triggers to handle events in attached behaviors?

推荐答案

问题是 EventTrigger 没有连接到 Behavior 的事件.相反，它连接到 Behavior 的 AssociatedObject 事件.这是相关的源代码:

The problem is that the EventTrigger doesn't hook up to the Behavior's events. Instead it is hooking up to the Behavior's AssociatedObject's events. Here is the relevant source code:

 protected override void OnAttached()
    {
        base.OnAttached();
        DependencyObject associatedObject = base.AssociatedObject;
        Behavior behavior = associatedObject as Behavior;
        FrameworkElement element = associatedObject as FrameworkElement;
        this.RegisterSourceChanged();
        if (behavior != null)
        {
            associatedObject = ((IAttachedObject) behavior).AssociatedObject;
            behavior.AssociatedObjectChanged += new EventHandler(this.OnBehaviorHostChanged);
        }
        ....
  }

所以你可以看到，如果触发器的关联对象是一个行为，那么它会将关联对象设置为行为的关联对象，也就是你的项目集合.项目集合没有拖动事件，因此不会触发任何事件.

So you can see that if the associated object of the trigger is a behavior, then it sets the associated object to the Behavior's associated object which is your items collection. The items collection doesn't have a dragging event so nothing is ever fired.

您可能可以通过创建另一个行为来获得您想要的结果，该行为检查关联的对象是否具有拖动行为，如果有，则将您的行为附加到拖动事件.然后从那里调用对象上的方法.

You could probably get the results you want by creating another behavior that checks to see if the associated object has a drag behavior and if so have your behavior attach to the dragging event. Then call the method on the object from there.

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