ios - UIView一开始就往下跳

Question

我需要更改 UIView 在 tableview 滚动时的位置。当我在动画 block 中更改 UIView 的帧大小时，它会下降，然后移动到正确的位置。请看我的代码。

- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
CGPoint scrollVelocity = [_collectionViewLeaderboard.panGestureRecognizer velocityInView:_collectionViewLeaderboard.superview];
if (scrollVelocity.y > 0.0f){
    NSLog(@"going down");
    [UIView animateWithDuration:0.3f
                              animations:^ {

                                  _headerview.frame = CGRectMake(0, 0, _headerview.frame.size.width, _headerview.frame.size.height);

                                  _headerviewSecond.frame = CGRectMake(0, _headerview.frame.size.height, _headerviewSecond.frame.size.width, _headerviewSecond.frame.size.height);

                                  self.collectionViewLeaderboard.frame = CGRectMake(self.view.frame.origin.x, _headerviewSecond.frame.size.height+_headerview.frame.size.height, self.view.frame.size.width, self.view.frame.size.height);

                                  frameconditon = _headerview.frame;

                              } completion:^ (BOOL completed) {

                              }];

}
else if (scrollVelocity.y < 0.0f){
    NSLog(@"going up");

    //CGAffineTransform transform = CGAffineTransformMake(1, 0, 0, 1, _headerview.frame.origin.x, _headerview.frame.origin.y);
        [UIView animateWithDuration:5.0 animations:^{
            NSLog(@"test");


            _headerview.frame = CGRectMake(0, -(_headerview.frame.size.height), _headerview.frame.size.width, _headerview.frame.size.height);

            _headerviewSecond.frame = CGRectMake(0, (_headerview.frame.size.height)-40, _headerviewSecond.frame.size.width, _headerviewSecond.frame.size.height);

        } completion:^(BOOL finished) {

        }];


         self.collectionViewLeaderboard.frame = CGRectMake(self.view.frame.origin.x, _headerviewSecond.frame.size.height, self.view.frame.size.width, self.view.frame.size.height);

 }
 }

headerview 应该移动到 View 的顶部并且它可以工作但是当我第一次运行它时，它会下降并返回到正确的位置。我将如何在滚动时更改约束。

Answer 1

对于基于约束的 View ，尝试使用 socket 通过更改约束常量属性来设置动画。