iOS UIScrollView知识点

1-bounces取消下拉弹簧效果

- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
        
   CGFloat offsetY = scrollView.contentOffset.y;

    if ( offsetY < 0 ) {
        // 1 头部下拉失效，但 微微卡顿抖动，同时下拉失效后，手指在屏幕上继续上滑也失效，只有手指离开屏幕后才可以上滑
        scrollView.bounces = NO;
        scrollView.scrollEnabled = NO;

        // 2 同1，但卡顿有所改善
        scrollView.bounces = NO;
        scrollView.scrollEnabled = NO;
        [scrollView setContentOffset:CGPointZero];
        
        // 3 解决了1和2的卡顿和滑动问题
        scrollView.bounces = NO;
        [scrollView setContentOffset:CGPointZero];
    }
    else {
        
        // 1,2
        scrollView.bounces = YES;
        scrollView.scrollEnabled = YES;
        
        // 3
        scrollView.bounces = YES;
    }
}