Freddie's Ria World

3.15使用延迟实例化提高启动效率

发表时间：18. 12月, 2009 作者：Freddie.

问题
我们要保证组件仅仅在需要显示在屏幕上的时候才被创建。
Container 类默认情况下仅仅在要显示组件的时候创建它，因为UIComponent 默认的
creationPolicy 值为auto。换句话说，当视图(view)设置成可视的时候，如果还没有创建
该视图，则组件会实例化此视图
code:
<mx:Canvas xmlns:mx=”http://www.adobe.com/2006/mxml”
           height=”600″
           width=”600″>
    <mx:Script>
        <![CDATA[
            private function changeViewStackCreation():void
            {
                viewStack.creationPolicy=(comboBox.selectedItem as String);
                viewStack.createComponentsFromDescriptors(true);
            }
            private function changeViewStack():void
            {
                viewStack.selectedIndex=comboBoxChangeIndex.selectedIndex;
            }
        ]]>
    </mx:Script>
    <mx:Fade alphaFrom=”0″
             alphaTo=”1″
             duration=”4000″
             id=”fadeIn”/>
    <mx:ComboBox dataProvider=”{['none', 'all', 'queued',
'auto']}”
                 change=”changeViewStackCreation()”
                 id=”comboBox”/>
    <mx:ComboBox dataProvider=”{[1, 2, 3, 4]}”
                 x=”150″
                 change=”changeViewStack()”
                 id=”comboBoxChangeIndex”/>
    <mx:ViewStack id=”viewStack”
                  width=”400″
                  height=”300″
                  creationPolicy=”none”
                  y=”100″>
        <mx:Canvas creationCompleteEffect=”{fadeIn}”
                   creationIndex=”0″
                   backgroundColor=”#0000ff”
                   [...]

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