add onLoadEnd in Layer

Author: fuzhenn

src/layer/Layer.js

@@ -77,13 +77,15 @@ class Layer extends JSONAble(Eventable(Renderable(Class))) {
             return this;
         }
         if (this.onLoad()) {
+            this._initRenderer();
             const zIndex = this.getZIndex();
             if (!isNil(zIndex)) {
                 this._renderer.setZIndex(zIndex);
                 if (!this.isCanvasRender()) {
                     this._renderer.render();
                 }
             }
+            this.onLoadEnd();
         }
         return this;
     }
@@ -414,6 +416,9 @@ class Layer extends JSONAble(Eventable(Renderable(Class))) {
         return true;
     }
 
+    onLoadEnd() {
+    }
+
     /**
      * Whether the layer is loaded
      * @return {Boolean}
@@ -448,7 +453,6 @@ class Layer extends JSONAble(Eventable(Renderable(Class))) {
             this.setZIndex(zIndex);
         }
         this._switchEvents('on', this);
-        this._initRenderer();
 
         this.onAdd();