3.0 自带Physics设置无效的问题，求帮助

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我继承了Scene类
然后create
bool GameScene::init()
{
bool ret = false;
do
{
CC_BREAK_IF(!Scene::initWithPhysics());

m_SceneUI = cocostudio::GUIReader::getInstance()->widgetFromJsonFile(“GameSceneUI/GameSceneUI.ExportJson”);
this->addChild(m_SceneUI);

this->getPhysicsWorld()->setDebugDrawMask(PhysicsWorld::DEBUGDRAW_ALL);
this->getPhysicsWorld()->setGravity(Vect(0, -900));

发现那个按钮停在那边没有动，而且碰撞圈也没显示出来.求指教

Sprite *spr = Sprite::create(“CloseNormal.png”);
spr->setPosition(100, 300);
this->addChild(spr);
PhysicsBody *body = PhysicsBody::createCircle(spr->getContentSize().width / 2);
spr->setPhysicsBody(body);

ret = true;
} while (0);

return ret;
}

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求帮助啊！！！直接在APP里面写也没用啊
auto scene = Scene::createWithPhysics();
Director::getInstance()->runWithScene(scene);
scene->getPhysicsWorld()->setGravity(Vect(0, -10));

auto layer = Layer::create();
scene->addChild(layer);
Sprite *spr = Sprite::create("CloseNormal.png");
spr->setPosition(100, 300);
layer->addChild(spr);
PhysicsBody *body = PhysicsBody::createCircle(spr->getContentSize().width / 2);
spr->setPhysicsBody(body);

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坑，加入场景之前必须设置刚体，之后设置无效
这个是个什么道理。。。。
纠结了我一个下午，太坑了