滚动视图显示的坐标问题

Cocos2d-x
#1

我在init中这样写的

    scrollView = CCScrollView::create();
    CCLayer * _layer = CCLayer::create();
    char str = {0};
    for (int i = 2;i < 12 ;i++)
    {
        //sprintf(str,"",i); 
        CCSprite * shopSp = CREATE_SPRITE_FROM_CACHE("y_c_2_h.png");
        shopSp->setPosition(ccp(size.width/2,size.height/2 + 100 - 100*i));
        _layer->addChild(shopSp);
    }
    _layer->setAnchorPoint(CCPointZero);  
    _layer->setPosition(CCPointZero);  

    scrollView->setPosition(CCPointZero);
    scrollView->setContentOffset(CCPointZero);
    _layer->setContentSize(CCSizeMake(500,800*2));
    scrollView->setContentSize(CCSizeMake(500,800));
    scrollView->setContainer(_layer);
    scrollView->setTouchEnabled(true);                         
    scrollView->setDelegate(this);  
    scrollView->setDirection(kCCScrollViewDirectionVertical);  
    this->addChild(scrollView);

但是运行后的结果却是这样的，显示是左下角，我想它居中显示的，_layer->setPosition(CCPointZero); 改这写成居中的坐标，直接看不到滚动视图了，这是为什么呢？