Downloading progress (when preLoad many scenes)

Downloading progress (when preLoad many scenes)
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am making fb instant game and i wonder if there is anyway to show a progress of downloading files when calling cc.director.preloadScene
i found only a way to show a progress of loading scene by this method cc.loader.onProgress

preloadScene(sceneName: string, onProgress?: (completedCount: number, totalCount: number, item: any) => void, onLoaded?: (error: Error, asset: SceneAsset) => void): void;		

use onProgress callback, it can help you to know a progress of scene loading, the same as use cc.loader.load to load assets.

use it like

        var progress = 0;// a progress of scene loading,0 ~ 1;
        cc.director.preloadScene('SceneA', (completedCount: number, totalCount: number, item: any) => {
            progress = completedCount / totalCount;
        }, (error: Error, asset: cc.SceneAsset) => {
            //do something after preloaded scene
        });