cocos2d-x 3.2 android 为什么需要reload资源

Cocos2d-x
#1

void Java_org_cocos2dx_lib_Cocos2dxRenderer_nativeInit(JNIEnv* env, jobject thiz, jint w, jint h)
{
auto director = cocos2d::Director::getInstance();
auto glview = director->getOpenGLView();
if (!glview)
{
glview = cocos2d::GLView::create(“Android app”);
glview->setFrameSize(w, h);
director->setOpenGLView(glview);

    cocos_android_app_init(env, thiz);

    cocos2d::Application::getInstance()->run();
}
else
{
    AndroidReloadLayer::create();
    cocos2d::GL::invalidateStateCache();
    cocos2d::GLProgramCache::getInstance()->reloadDefaultGLPrograms();
    cocos2d::DrawPrimitives::init();
    cocos2d::VolatileTextureMgr::reloadAllTextures();

    cocos2d::EventCustom recreatedEvent(EVENT_RENDERER_RECREATED);
    director->getEventDispatcher()->dispatchEvent(&recreatedEvent);
    director->setGLDefaultValues();
}

}

android从后台返回前台的时候为什么需要reload资源。。。