ios中frame设置宽高计算的Demo

- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
int totalHeightOfScrollView = scrollView.contentSize.height - self.footerImageView.image.size.height;
float footerImageViewY = (totalHeightOfScrollView - scrollView.contentOffset.y);
float footerImageViewX = 0;
float bottomEdge = scrollView.contentOffset.y + scrollView.frame.size.height;

if (bottomEdge >= scrollView.contentSize.height) {
footerImageViewY = scrollView.frame.size.height - self.footerImageView.image.size.height;
}

if (self.footerImageView.image.size.width < self.view.frame.size.width) {
footerImageViewX = (self.view.frame.size.width/2)-(self.footerImageView.image.size.width/2);
}

[self.view addSubview:self.footerImageView];
self.footerImageView.frame = CGRectMake(footerImageViewX, footerImageViewY, self.footerImageView.image.size.width, self.footerImageView.image.size.height);
}