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關(guān)于Flex 初始化的research

 更新時間：2009年09月28日 18:01:46   作者：  
前些天在寫一個自定義的UI組件的時候，發(fā)現(xiàn)在override createChildren的,只能取到基本類型的自定義變量，而取不到Object類型的自定義變量。
后來研究發(fā)現(xiàn)，不是取不到，而是在createChildren的時候，自定義的objcet還沒有被賦值，只有當該組件的init事件之后才會被賦值，代碼如下：
APP:
復(fù)制代碼 代碼如下:

<?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：
復(fù)制代碼 代碼如下:

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：
復(fù)制代碼 代碼如下:

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 )");
        }
    }
}

最后運行的結(jié)果是：
CustomPanel[ PreInit ]
CustomPanel[ Begin to createChildren ]
CustomButton( Begin to Constructor )
CustomButton( The end of Constructor )
CustomButton( set customString ) //基本變量（String，Number（int，uint），Boolean）在PreInit 之前就被賦值
CustomButton( PreInit )
CustomButton( Begin to createChildren )
CustomButton( The end of createChildren )
CustomButton( Init )
CustomButton( set customObject ) //自定義對象變量在 Init之后才能被賦值，所以在createChildren中取不到
CustomPanel[ Init ] //有子控件的時候，Init 事件是在createChildren中發(fā)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 ] //證明layoutChrome是在updateDisplayList 中被調(diào)用的
CustomPanel[ The end of updateDisplayList ]
CustomButton( Begin to updateDisplayList )
CustomButton( The end of updateDisplayList )
CustomButton( Creation Complete )
CustomPanel[ CreationComplete ]
后來又發(fā)現(xiàn)，在MXML中設(shè)置基本變量和對象變量有一定區(qū)別，那就是對象變量必須要用大括號{}包起來，于是就想，會不會是綁定造成的，將APP改成如下,發(fā)現(xiàn)跟預(yù)想中的一樣，最后的輸出結(jié)果與上面的一樣：
復(fù)制代碼 代碼如下:

<?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";//將原對象換成字符串
        ]]-->
    </mx:Script>
    <com:CustomPanel width="100%" height="100%" label="FlexInitResearch">
        <com:CustomButton label="Button"
            customString="customString test" customObject="{o}"/>
    </com:CustomPanel>
</mx:Application>

為了進一步確定是由于綁定造成的賦值時期不一致，我又做了如下的一個試驗，不使用綁定給對象變量賦值：
復(fù)制代碼 代碼如下:

<?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>

其結(jié)果為:
CustomPanel[ PreInit ]
CustomPanel[ Begin to createChildren ]
CustomButton( Begin to Constructor )
CustomButton( The end of Constructor )
CustomButton( set customString )
CustomButton( set customObject ) //賦值時間與基本變量相同
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 ]
問題確定，所以以后再createChildren 中使用自定義對象變量的時候必須要注意，否則就會出現(xiàn)空指針之類的問題了。

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