后来研究发现，不是取不到，而是在createChildren的时候，自定义的objcet还没有被赋值，只有当该组件的init事件之后才会被赋值，代码如下：
APP:
<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
layout="absolute" xmlns:com="com.*">
<mx:Script>
<!--[CDATA[
[Bindable]
private var o:Object = {};
]]-->
</mx:Script>
<com:CustomPanel width="100%" height="100%" label="FlexInitResearch">
<com:CustomButton label="Button"
customString="customString test" customObject="{o}"/>
</com:CustomPanel>
</mx:Application>
CustomPanel：
package com
{
import mx.containers.Panel;
import mx.events.FlexEvent;
public class CustomPanel extends Panel
{
public function CustomPanel()
{
super();
this.addEventListener(FlexEvent.PREINITIALIZE, onPreInit);
this.addEventListener(FlexEvent.INITIALIZE, onInit);
this.addEventListener(FlexEvent.CREATION_COMPLETE, onCreationComplete);
this.addEventListener(FlexEvent.APPLICATION_COMPLETE, onAppInitComplete);
}
//=================================
// event handler
//=================================
private function onPreInit(event:FlexEvent):void
{
trace("CustomPanel[ PreInit ]");
}
private function onInit(event:FlexEvent):void
{
trace("CustomPanel[ Init ]");
}
private function onCreationComplete(event:FlexEvent):void
{
trace("CustomPanel[ CreationComplete ]");
}
private function onAppInitComplete(event:FlexEvent):void
{
trace("CustomPanel[ AppInitComplete ]");
}
//=================================
// override function
//=================================
override protected function createChildren():void
{
trace("CustomPanel[ Begin to createChildren ]");
super.createChildren();
trace("CustomPanel[ The end of createChildren ]");
}
override protected function measure():void
{
trace("CustomPanel[ Begin to measure ]");
super.measure();
trace("CustomPanel[ The end of measure ]");
}
override protected function updateDisplayList(unscaledWidth:Number, unscaledHeight:Number):void
{
trace("CustomPanel[ Begin to updateDisplayList ]");
super.updateDisplayList(unscaledWidth, unscaledHeight);
trace("CustomPanel[ The end of updateDisplayList ]");
}
override protected function layoutChrome(unscaledWidth:Number, unscaledHeight:Number):void
{
trace("CustomPanel[ Begin to layoutChrome ]");
super.layoutChrome(unscaledWidth, unscaledHeight);
trace("CustomPanel[ The end of layoutChrome ]");
}
override protected function commitProperties():void
{
trace("CustomButton[ Begin to commitProperties ]");
super.commitProperties();
trace("CustomButton[ The end of commitProperties ]");
}
}
}
CustomButton：
package com
{
import mx.controls.Button;
import mx.events.FlexEvent;
public class CustomButton extends Button
{
//=================================
// properties
//=================================
private var _customString:String = "";
private var _customObject:Object = null;
public function get customString():String
{
return _customString;
}
//string
public function set customString(value:String):void
{
trace("CustomButton( set customString )");
_customString = value;
}
//object
public function get customObject():Object
{
return _customObject;
}
public function set customObject(value:Object):void
{
trace("CustomButton( set customObject )");
_customObject = value;
}
//=================================
// Constructor
//=================================
public function CustomButton()
{
trace("CustomButton( Begin to Constructor )");
super();
this.addEventListener(FlexEvent.PREINITIALIZE, onPreInit);
this.addEventListener(FlexEvent.INITIALIZE, onInit);
this.addEventListener(FlexEvent.CREATION_COMPLETE, onCreationComplete);
this.addEventListener(FlexEvent.APPLICATION_COMPLETE, onAppInitComplete);
trace("CustomButton( The end of Constructor )");
}
//=================================
// event handler
//=================================
private function onPreInit(event:FlexEvent):void
{
trace("CustomButton( PreInit )");
}
private function onInit(event:FlexEvent):void
{
trace("CustomButton( Init )");
}
private function onCreationComplete(event:FlexEvent):void
{
trace("CustomButton( Creation Complete )");
}
private function onAppInitComplete(event:FlexEvent):void
{
trace("CustomButton( AppInitComplete )");
}
//=================================
// override function
//=================================
override protected function createChildren():void
{
trace("CustomButton( Begin to createChildren )");
super.createChildren();
trace("CustomButton( The end of createChildren )");
}
override protected function measure():void
{
trace("CustomButton( Begin to measure )");
super.measure();
trace("CustomButton( The end of measure )");
}
override protected function updateDisplayList(unscaledWidth:Number, unscaledHeight:Number):void
{
trace("CustomButton( Begin to updateDisplayList )");
super.updateDisplayList(unscaledWidth, unscaledHeight);
trace("CustomButton( The end of updateDisplayList )");
}
override protected function commitProperties():void
{
trace("CustomButton( Begin to commitProperties )");
super.commitProperties();
trace("CustomButton( The end of commitProperties )");
}
}
}
最后运行的结果是：
CustomPanel[ PreInit ]
CustomPanel[ Begin to createChildren ]
CustomButton( Begin to Constructor )
CustomButton( The end of Constructor )
CustomButton( set customString ) //基本变量（String，Number（int，uint），Boolean）在PreInit 之前就被赋值
CustomButton( PreInit )
CustomButton( Begin to createChildren )
CustomButton( The end of createChildren )
CustomButton( Init )
CustomButton( set customObject ) //自定义对象变量在 Init之后才能被赋值，所以在createChildren中取不到
CustomPanel[ Init ] //有子控件的时候，Init 事件是在createChildren中发出的
CustomPanel[ The end of createChildren ]
CustomButton( set customObject )
CustomButton[ Begin to commitProperties ]
CustomButton[ The end of commitProperties ]
CustomButton( Begin to commitProperties )
CustomButton( The end of commitProperties )
CustomButton( Begin to measure )
CustomButton( The end of measure )
CustomPanel[ Begin to measure ]
CustomPanel[ The end of measure ]
CustomPanel[ Begin to updateDisplayList ]
CustomPanel[ Begin to layoutChrome ]
CustomPanel[ The end of layoutChrome ] //证明layoutChrome是在updateDisplayList 中被调用的
CustomPanel[ The end of updateDisplayList ]
CustomButton( Begin to updateDisplayList )
CustomButton( The end of updateDisplayList )
CustomButton( Creation Complete )
CustomPanel[ CreationComplete ]
后来又发现，在MXML中设置基本变量和对象变量有一定区别，那就是对象变量必须要用大括号{}包起来，于是就想，会不会是绑定造成的，将APP改成如下,发现跟预想中的一样，最后的输出结果与上面的一样：
<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
layout="absolute" xmlns:com="com.*">
<mx:Script>
<!--[CDATA[
[Bindable]
private var o:String = "String test";//将原对象换成字符串
]]-->
</mx:Script>
<com:CustomPanel width="100%" height="100%" label="FlexInitResearch">
<com:CustomButton label="Button"
customString="customString test" customObject="{o}"/>
</com:CustomPanel>
</mx:Application>
为了进一步确定是由于绑定造成的赋值时期不一致，我又做了如下的一个试验，不使用绑定给对象变量赋值：
<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
layout="absolute" xmlns:com="com.*">
<com:CustomPanel width="100%" height="100%" label="FlexInitResearch">
<com:CustomButton label="Button"
customString="customString test">
<com:customObject>
<mx:ArrayCollection/>
</com:customObject>
</com:CustomButton>
</com:CustomPanel>
</mx:Application>
其结果为:
CustomPanel[ PreInit ]
CustomPanel[ Begin to createChildren ]
CustomButton( Begin to Constructor )
CustomButton( The end of Constructor )
CustomButton( set customString )
CustomButton( set customObject ) //赋值时间与基本变量相同
CustomButton( PreInit )
CustomButton( Begin to createChildren )
CustomButton( The end of createChildren )
CustomButton( Init )
CustomPanel[ Init ]
CustomPanel[ The end of createChildren ]
CustomButton[ Begin to commitProperties ]
CustomButton[ The end of commitProperties ]
CustomButton( Begin to commitProperties )
CustomButton( The end of commitProperties )
CustomButton( Begin to measure )
CustomButton( The end of measure )
CustomPanel[ Begin to measure ]
CustomPanel[ The end of measure ]
CustomPanel[ Begin to updateDisplayList ]
CustomPanel[ Begin to layoutChrome ]
CustomPanel[ The end of layoutChrome ]
CustomPanel[ The end of updateDisplayList ]
CustomButton( Begin to updateDisplayList )
CustomButton( The end of updateDisplayList )
CustomButton( Creation Complete )
CustomPanel[ CreationComplete ]
问题确定，所以以后再createChildren 中使用自定义对象变量的时候必须要注意，否则就会出现空指针之类的问题了。
