Flex中的target和currenttarget有什么区别？

发布于 2024-08-22 22:16:33 字数 50 浏览 4 评论 0原文

谁能告诉我 Flex 中 target 和 currenttarget 之间的区别吗？

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葬花如无物 2024-08-29 22:16:33

当然，我也遇到过一些麻烦。 currentTarget 属性是您为其注册事件处理程序的 IEventListener。 目标 是调度您当前正在处理的事件的目标。因此，currentTarget 发生了变化，而 target 却没有变化。

查看以下示例：

示例应用程序

<?xml version="1.0" encoding="utf-8"?>
<mx:Application
    xmlns:mx="http://www.adobe.com/2006/mxml"
    creationComplete="addListeners()">

    <mx:Script>
        <![CDATA[

            protected function addListeners():void
            {
                greatGrandParent.addEventListener(Event.COMPLETE, completeHandler);
                grandParent.addEventListener(Event.COMPLETE, completeHandler);
                aParent.addEventListener(Event.COMPLETE, completeHandler);
                child.addEventListener(Event.COMPLETE, completeHandler);
                // dispatch event that "bubbles", second param is "true"
                // dispatched from child
                child.dispatchEvent(new Event(Event.COMPLETE, true));
            }

            protected function completeHandler(event:Event):void
            {
                trace("target: ", event.target + ", currentTarget: ", event.currentTarget);
            }

        ]]>
    </mx:Script>

    <mx:Panel id="greatGrandParent">
        <mx:Panel id="grandParent">
            <mx:Panel id="aParent">
                <mx:Button id="child"/>
            </mx:Panel>
        </mx:Panel>
    </mx:Panel>

</mx:Application>

输出

target:  MyApp.greatGrandParent.grandParent.aParent.child, currentTarget:  MyApp.greatGrandParent.grandParent.aParent.child
target:  MyApp.greatGrandParent.grandParent.aParent.child, currentTarget:  MyApp.greatGrandParent.grandParent.aParent
target:  MyApp.greatGrandParent.grandParent.aParent.child, currentTarget:  MyApp.greatGrandParent.grandParent
target:  MyApp.greatGrandParent.grandParent.aParent.child, currentTarget:  MyApp.greatGrandParent

这是一个简单的显示对象树，当应用程序准备就绪时，我：

在每个组件上添加相同事件的侦听器树。
调度任意事件（仅用于演示）。我选择了Event.COMPLETE。

由于所有内容都已为同一事件注册了一个 eventHandler，并且由于我已将“bubbles”设置为 true（“new Event(type, bubbles)”），因此树中的任何内容（从子级）对于为 Event.COMPLETE 注册了事件处理程序的 grandGrandParent 及更高版本，将运行该方法：completeHandler。事件沿着链条向上传播，然后返回。 target 是调度该事件的目标，因此由于 child 调度了它，因此它应该是常量。 currentTarget 是发生变化的部分。

这意味着，假设您想要检查何时滚动 Flex 中的 DataGrid，您想知道何时滚动 DataGrid 中的 itemRenderer 之一内的复选框。一种方法是在每个 itemRenderer 的 MouseEvent.ROLL_OVER 复选框上添加 EventListener。另一种方法是为 MouseEvent.ROLL_OVER 添加事件监听器到 DataGrid 本身，并检查事件的目标：

protected function dataGrid_rollOverHandler(event:MouseEvent):void
{
    // event.currentTarget is DataGrid
    if (event.target is CheckBox)
        trace("rolled over checkbox!");
}

这就是我经常使用 event.target< /代码>。

希望有帮助，
槊

Sure, I've had some trouble with this too. The currentTarget property is the IEventListener you registered the event handler for. The target is the one that dispatched the event that you are currently handling. So the currentTarget changes, the target doesn't.

Check out the following example:

Sample App

<?xml version="1.0" encoding="utf-8"?>
<mx:Application
    xmlns:mx="http://www.adobe.com/2006/mxml"
    creationComplete="addListeners()">

    <mx:Script>
        <![CDATA[

            protected function addListeners():void
            {
                greatGrandParent.addEventListener(Event.COMPLETE, completeHandler);
                grandParent.addEventListener(Event.COMPLETE, completeHandler);
                aParent.addEventListener(Event.COMPLETE, completeHandler);
                child.addEventListener(Event.COMPLETE, completeHandler);
                // dispatch event that "bubbles", second param is "true"
                // dispatched from child
                child.dispatchEvent(new Event(Event.COMPLETE, true));
            }

            protected function completeHandler(event:Event):void
            {
                trace("target: ", event.target + ", currentTarget: ", event.currentTarget);
            }

        ]]>
    </mx:Script>

    <mx:Panel id="greatGrandParent">
        <mx:Panel id="grandParent">
            <mx:Panel id="aParent">
                <mx:Button id="child"/>
            </mx:Panel>
        </mx:Panel>
    </mx:Panel>

</mx:Application>

Output

target:  MyApp.greatGrandParent.grandParent.aParent.child, currentTarget:  MyApp.greatGrandParent.grandParent.aParent.child
target:  MyApp.greatGrandParent.grandParent.aParent.child, currentTarget:  MyApp.greatGrandParent.grandParent.aParent
target:  MyApp.greatGrandParent.grandParent.aParent.child, currentTarget:  MyApp.greatGrandParent.grandParent
target:  MyApp.greatGrandParent.grandParent.aParent.child, currentTarget:  MyApp.greatGrandParent

It's a simple tree of display objects, and when the app is ready I:

Add listeners for the same event on each component in the tree.
Dispatch an arbitrary event (just for demonstration). I chose Event.COMPLETE.

Since everything has registered an eventHandler for that same event, and since I have set bubbles to true (new Event(type, bubbles)), anything in the tree, from child to greatGrandParent and beyond, that has registered an event handler for Event.COMPLETE, will run that method: completeHandler. Events travel up the chain then back down. The target is the one that dispatched the event, so since child dispatched it, it should be constant. The currentTarget is what changes.

This means that, say you want to check when you are rolling over a DataGrid in Flex, you want to know when you roll over a Checkbox inside one of the itemRenderers in the DataGrid. One way is to addEventListener on every itemRenderer's checkbox for MouseEvent.ROLL_OVER. Another way is to addEventListener to the DataGrid itself for MouseEvent.ROLL_OVER, and check what the target is on the event:

protected function dataGrid_rollOverHandler(event:MouseEvent):void
{
    // event.currentTarget is DataGrid
    if (event.target is CheckBox)
        trace("rolled over checkbox!");
}

That's how I often use event.target.

Hope that helps,
Lance

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