Iphone UIImageView没有'；t正确响应center.x

我试图让一个图像环绕窗口（当它从左边掉下来时，它会重新出现在右边），我有一个计时器调用一个包含以下内容的函数：

bgImage.center = CGPointMake(bgImage.center.x - 5, bgImage.center.y);
if (bgImage.center.x < -self.view.frame.size.width/2)
    bgImage.center = CGPointMake(bgImage.center.x + self.view.frame.size.width, bgImage.center.y);
    NSLog(@"%f",bgImage.center.x);

---

这个怎么样？它将考虑图像的大小

bgImage.frame = CGRectMake(bgImage.origin.x - 5.0f, bgImage.origin.y, bgImage.size.width, bgImage.size.height);

if ( (bgImage.frame.origin.x + bgImage.frame.size.width) < 0.0f) {
    bgImage.frame = CGRectMake(self.view.frame.size.width, bgImage.origin.y, bgImage.size.width, bgImage.size.height);
}

bgImage.frame=CGRectMake（bgImage.origin.x-5.0f，bgImage.origin.y，bgImage.size.width，bgImage.size.height）；
if（（bgImage.frame.origin.x+bgImage.frame.size.width）<0.0f）{
bgImage.frame=CGRectMake（self.view.frame.size.width，bgImage.origin.y，bgImage.size.width，bgImage.size.height）；
}

bgImage.frame = CGRectMake(bgImage.origin.x - 5.0f, bgImage.origin.y, bgImage.size.width, bgImage.size.height);

if ( (bgImage.frame.origin.x + bgImage.frame.size.width) < 0.0f) {
    bgImage.frame = CGRectMake(self.view.frame.size.width, bgImage.origin.y, bgImage.size.width, bgImage.size.height);
}