target和currentTarget的区别
开始学习Flex,会在别人的代码中经常看到target和currentTarget这两个属性,一般是event.target、event.currentTarget,那他们两个有什么区别呢?
简单说,target是事件的调用对象(event dispatcher),currentTarget是事件的处理对象(event processor)
以一个实例来说吧
说明:
简单说,target是事件的调用对象(event dispatcher),currentTarget是事件的处理对象(event processor)
以一个实例来说吧
1 <?xml version="1.0" encoding="utf-8"?>
2 <mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="vertical" name="app"
3 initialize="init()">
4
5 <mx:Button id="btn" name="btn" label="按钮1"/>
6
7 <mx:Button id="btn2" name="btn2" label="按钮2" click="clickHandler(event)" />
8
9 <mx:Script>
10 <![CDATA[
11 import mx.controls.Alert;
12 private function init(): void
13 {
14 addEventListener(MouseEvent.CLICK, clickHandler);
15 }
16
17 private function clickHandler(event: MouseEvent): void
18 {
19 Alert.show("target: " + (event.target as DisplayObject).name
20 + "\ncurrentTarget: " + (event.currentTarget as DisplayObject).name);
21 }
22 ]]>
23 </mx:Script>
24 </mx:Application>
25
2 <mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="vertical" name="app"
3 initialize="init()">
4
5 <mx:Button id="btn" name="btn" label="按钮1"/>
6
7 <mx:Button id="btn2" name="btn2" label="按钮2" click="clickHandler(event)" />
8
9 <mx:Script>
10 <![CDATA[
11 import mx.controls.Alert;
12 private function init(): void
13 {
14 addEventListener(MouseEvent.CLICK, clickHandler);
15 }
16
17 private function clickHandler(event: MouseEvent): void
18 {
19 Alert.show("target: " + (event.target as DisplayObject).name
20 + "\ncurrentTarget: " + (event.currentTarget as DisplayObject).name);
21 }
22 ]]>
23 </mx:Script>
24 </mx:Application>
25
说明:
- 点击btn,btn是事件发送者,因此,target是btn;
- app注册了事件监听器,用于监听MouseEvnet.Click事件,是事件处理者,因此currentTarget是app
- btn2自己注册了click事件,那么btn2既是事件发送者,又是处理者,因此,target和currentTarget都是btn2,这种情况下,两者是一致的
- 同时注意,由于app注册了鼠标点击事件,在点击btn2的时候,首先响应的是app的处理器,然后才是btn2的处理器