关于gui的skinnableContainer的一点问题

创建一个UIAsset

 var uiAsset = new egret.gui.UIAsset();uiAsset.source = "bgImage";

把UIAsset添加到SkinnableContainer上

 var container = new egret.gui.SkinnableContainer();container.addElement(uiAsset);

然后把container添加到stage上会发现uiAsset并没有显示出来。这是什么原因呢？

这时我去看了一下SkinnableContainer的代码，发现

public addElement(element:IVisualElement):IVisualElement {return this._getCurrentContentGroup().addElement(element);
}public _getCurrentContentGroup():Group {if (this.contentGroup == null) {if (this._placeHolderGroup == null) {this._placeHolderGroup = new Group();this._placeHolderGroup.visible = false;this._addToDisplayList(<DisplayObject><any>this._placeHolderGroup);}this._placeHolderGroup.addEventListener(ElementExistenceEvent.ELEMENT_ADD, this._contentGroup_elementAddedHandler, this);this._placeHolderGroup.addEventListener(ElementExistenceEvent.ELEMENT_REMOVE, this._contentGroup_elementRemovedHandler, this);return this._placeHolderGroup;}else {return this.contentGroup;　　　　　　}
}

SkinnableContainer的addElement是默认如果没有contentGroup的话是加在_placeHolderGroup上的，而placeHolderGroup默认的visible是false的，而在partAdded中如果发现有皮肤里有contentGroup，则会把placeHolderGroup的children放到contentGroup里。

皮肤里若没有contentGroup，则skinnableContainer所有的addElement的子项都不会显示。

我们给container赋一个皮肤。

 var container = new egret.gui.SkinnableContainer();container.skinName = testSkin;container.addElement(uiAsset);//皮肤类
class testSkin extends egret.gui.Skin {private contentGroup:egret.gui.Group;public get skinParts() {return ["contentGroup"]}constructor() {super();}public createChildren():void {super.createChildren();var group = new egret.gui.Group();this.contentGroup = group;this.addElement(group);}
}