?1?????public?function?Application()
?2?????{
?3?????????UIComponentGlobals.layoutManager?=?ILayoutManager(
?4?????????????Singleton.getInstance("mx.managers::ILayoutManager"));
?5?????????UIComponentGlobals.layoutManager.usePhasedInstantiation?=?true;
?6?
?7?????????if?(!FlexGlobals.topLevelApplication)
?8?????????????FlexGlobals.topLevelApplication?=?this;
?9?
10?????????super();
11?????????????????????
12?????????showInAutomationHierarchy?=?true;
13?????}
布局分三個階段執行:提交、度量和布局。?2?????{
?3?????????UIComponentGlobals.layoutManager?=?ILayoutManager(
?4?????????????Singleton.getInstance("mx.managers::ILayoutManager"));
?5?????????UIComponentGlobals.layoutManager.usePhasedInstantiation?=?true;
?6?
?7?????????if?(!FlexGlobals.topLevelApplication)
?8?????????????FlexGlobals.topLevelApplication?=?this;
?9?
10?????????super();
11?????????????????????
12?????????showInAutomationHierarchy?=?true;
13?????}
那作為一個組件,是怎么樣 參與到布局策略中呢?
flex中所有的組件都繼承自UIComponent類,在該類上實現了一個叫IInvalidating的接口:
public?interface?IInvalidating
{
????function?invalidateProperties():void;
????function?invalidateSize():void;
????function?invalidateDisplayList():void;
????????function?validateNow():void;
}
當組件調用invalidateProperties方法,表明該組件一個屬性發生變化,需要更新.{
????function?invalidateProperties():void;
????function?invalidateSize():void;
????function?invalidateDisplayList():void;
????????function?validateNow():void;
}
它會在方法體寫上這么一句:
?? UIComponentGlobals.layoutManager.invalidateProperties(this);
來告訴布局管理器(LayoutManager),布局管理器在適當的時候回調組件上的validateProperties()驗證屬性,
如果有屬性有變化,進而再調用commitProperties()提交變化的屬性.
同理,
調用invalidateSize()告訴布局管理器組件大小發生了變化.
調用invalidateDisplayList()告訴布局管理器組件布局發生了變化.