在scrollViewDidScroll中更改UIScrollView框架可消除顶部的弹跳

Question

Something strange happening, when I scroll in a UIScrollView I want to move it up and expand it's height because it's too small by default. It works fine and I listen to the scrollViewDidScroll delegate but that disables the bouncing on top!

Even if I do this in scrollViewDidScroll top bouncing is gone, bottom still bounces:

scrollView.frame = CGRectOffset(self.scrollView.frame, 0, 0);

This is my actual code in scrollViewDidScroll:

self.maxScrollDistance = 400;

if(scrollView.contentOffset.y <= self.maxScrollDistance) {
    float newY = self.startScrollViewY - scrollView.contentOffset.y / 3;
    float newScrollViewHeight = self.view.frame.size.height - newY;
    scrollView.frame = CGRectMake(0, newY, self.scrollView.frame.size.width, newScrollViewHeight);
}

Anyone a hint to what might be the problem, a video of the problem in action: Bounce Problem Simulator recording

Thanks guys!

Answer 1

Your frame is always changing when scrolling to bottom, and it's not bouncing because changing frame when scrolling in negative contentOffset.y

if(scrollView.contentOffset.y <= self.maxScrollDistance)

Try to catch when scrollView.contentOffset.y < 0 and set its changes frame.

if(scrollView.contentOffset.y < self.maxScrollDistance && scrollView.contentOffset.y>0) {
    // Todo
}else if(scrollView.contentOffset.y <= -self.maxScrollDistance && scrollView.contentOffset.y<0){
    // Todo
}

// Try this code :

if(scrollView.contentOffset.y < self.maxScrollDistance && scrollView.contentOffset.y>0) {
    float newY = self.startScrollViewY - scrollView.contentOffset.y / 3;
    float newScrollViewHeight = self.view.frame.size.height - newY;
    scrollView.frame = CGRectMake(0, newY, self.scrollView.frame.size.width, newScrollViewHeight);

}else if(scrollView.contentOffset.y <= -self.maxScrollDistance && scrollView.contentOffset.y<0){
    float newY = self.startScrollViewY + scrollView.contentOffset.y / 3;
    float newScrollViewHeight = self.view.frame.size.height + newY;
    scrollView.frame = CGRectMake(0, newY, self.scrollView.frame.size.width, newScrollViewHeight);
}