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关于Flex 初始化的research

时间：2020-02-02 13:12 编辑：来源：阅读：
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摘要：关于Flex 初始化的research

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： [b]APP:[/b]

<?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>

[b]CustomPanel：[/b]

[u]复制代码[/u] 代码如下:

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：

[u]复制代码[/u] 代码如下:

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：

[u]复制代码[/u] 代码如下:

<?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";//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：

[u]复制代码[/u] 代码如下:

<?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。

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