问UIScrollView变焦问题(IOS 8 GM)

EN

- (void)scrollViewDidZoom:(UIScrollView *)scrollView{
    [self layoutSubviews];
}

- (void)layoutSubviews
{
[super layoutSubviews];

// center the image as it becomes smaller than the size of the screen
CGSize boundsSize = super.bounds.size;
CGRect frameToCenter = imageView.frame;

// center horizontally
if (frameToCenter.size.width < boundsSize.width){
    frameToCenter.origin.x = (boundsSize.width - frameToCenter.size.width) / 2;
}
else {
    frameToCenter.origin.x = 0;
}
// center vertically
if (frameToCenter.size.height < boundsSize.height){
    frameToCenter.origin.y = (boundsSize.height - frameToCenter.size.height) / 2;
}
else {
    frameToCenter.origin.y = 0;
}
imageView.frame = frameToCenter;
}

- (void)scrollViewDidZoom:(UIScrollView *)scrollView {
    [self setNeedsLayout]; // triggers a layout update during the next update cycle
    [self layoutIfNeeded]; // lays out the subviews immediately
}