flex初始化时的事件测试

flex组件在建立的时候都会经历四个事件：preinitialize, initialize, creationComplete和updateComplete （updateComplete事件在任何改动视觉的情况下都会发生，不是初始化时独有的）。我这里有个例子来检测在嵌套和平行的情况下，测试各个组件的事件抛出顺序。


程序代码


<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute"
    preinitialize="showEvent(event)"
    initialize="showEvent(event)"
    creationComplete="showEvent(event)"
    updateComplete="showEvent(event)">

    <mx:Script>
        <![CDATA[
            import flash.utils.getTimer;
            private function showEvent(event:Event):void
            {
                trace(flash.utils.getTimer().toString()+" >> "+event.currentTarget.name+" "+event.type);
            }
        ]]>
    </mx:Script>

    <mx:Canvas id="canv1"
        preinitialize="showEvent(event)"
        initialize="showEvent(event)"
        creationComplete="showEvent(event)"
        updateComplete="showEvent(event)">

        <mx:Button id="btn1"
            preinitialize="showEvent(event)"
            initialize="showEvent(event)"
            creationComplete="showEvent(event)"
            updateComplete="showEvent(event)"/>
    </mx:Canvas>

    <mx:Button id="btn2"
            preinitialize="showEvent(event)"
            initialize="showEvent(event)"
            creationComplete="showEvent(event)"
            updateComplete="showEvent(event)"/>

</mx:Application>

它的输出是：

    1299 >> eventTest0 preinitialize

    1307 >> canv1 preinitialize

    1310 >> btn1 preinitialize

    1318 >> btn1 initialize

    1319 >> canv1 initialize

    1320 >> btn2 preinitialize

    1321 >> btn2 initialize

    1321 >> eventTest0 initialize

    [SWF] G:\projects\eventTest\bin-debug\eventTest.swf - 588,818 bytes after decompression

    1387 >> btn1 creationComplete

    1387 >> btn1 updateComplete

    1387 >> canv1 creationComplete

    1387 >> canv1 updateComplete

    1388 >> btn2 creationComplete

    1388 >> btn2 updateComplete

    1388 >> eventTest0 creationComplete

    1390 >> eventTest0 updateComplete

看着有点混乱，不过仔细看看，可以把过程分成两个部分。很明显，所有的creationComplete和updateComplete发生在第二次update的时候，之前flex组件只是做一些设置和计算的工作，并没有在画布上画任何东西。除此以外，还有这么一些规律：

    * 就单个组件而言，事件的抛出顺序是preinitialize，initialize，creationComplete
    * 嵌套关系的两个组件（比如Canvas和button1），preinitialize先外后内，initialize和creationComplete先内后外。只是creationComplete要在下一次update才会发生。
    * 平行关系的两个组件（比如Canvas和button2），按mxml内的顺序，只有前面组件initialize结束后，后面的组件才会抛出preinitialize。