Objective-C：动画高度约束更改不起作用

Question

我有两个代码块，一个有效，第二个无效。首先添加一个视图，将其高度限制为 0，然后在动画块中取消此约束，使其长大。完美运行。第二个应该重新激活0 height constraint，使其高度缩回到0，然后将其删除，但它会立即被删除。代码如下：

self.pickupAddressViewModel.infoViewBlock = ^(MandatoryPickupView * _Nonnull pickupView) {
        if (weakSelf.mandatoryPickupView) {
            return;
        }
        weakSelf.mandatoryPickupView = pickupView;
        [weakSelf.view addSubview:pickupView];

        CGFloat gap = weakSelf.orderButton.originY;
        [[pickupView.bottomAnchor constraintEqualToAnchor:weakSelf.view.bottomAnchor constant:-gap] setActive:YES];
        [[pickupView.leadingAnchor constraintEqualToAnchor:weakSelf.view.leadingAnchor
                                                  constant:16.0] setActive:YES];
        [[pickupView.trailingAnchor constraintEqualToAnchor:weakSelf.view.trailingAnchor
                                                   constant:-16.0] setActive:YES];
        weakSelf.mandatoryPickupViewHeight = [pickupView.heightAnchor constraintEqualToConstant:0];
        [weakSelf.mandatoryPickupViewHeight setActive:YES];

        [weakSelf.view layoutIfNeeded];
        [UIView animateWithDuration:0.5 animations:^{
            [weakSelf.mandatoryPickupViewHeight setActive:NO];
            [weakSelf.view layoutIfNeeded];
        }];
    };
    self.pickupAddressViewModel.closeViewBlock = ^{
        if (!weakSelf.mandatoryPickupView) {
            return;
        }
        [weakSelf.view layoutIfNeeded];
        [UIView animateWithDuration:10.5
                         animations:^{
                             [weakSelf.mandatoryPickupViewHeight setActive:YES];
                             [weakSelf.view layoutIfNeeded];
                         } completion:^(BOOL finished) {
                             [weakSelf.mandatoryPickupView removeFromSuperview];
                             weakSelf.mandatoryPickupView = nil;
                             weakSelf.mandatoryPickupViewHeight = nil;
                         }];
    };

1. 这一切都发生在主线程上。
2. 我尝试将框架的高度设置为 0，但也没有用
3. weakSelf.mandatoryPickupViewHeight 是一个强大的属性，当我第二次激活时它不是 nil。

有什么建议吗？谢谢！

Answer 1

当你对动画使用自动布局时，你可以这样做：

1. 确保自动布局已完成：

   self.view.layoutIfNeeded()
   

2. 然后您在动画块之前更改约束。比如：

   someConstraint.constant = 0
   

3. 然后在更改约束后，告诉自动布局约束已更改：

   self.view.setNeedsLayout()
   

4. 然后您只需调用 layoutIfNeeded() 即可添加一个动画块：

   UIView.animate(withDuration: 1, animations: {
       self.view.layoutIfNeeded()
   })
   

请注意，您没有停用约束 - 它必须始终处于活动状态。

我猜你的代码中的问题就在这里：

    [UIView animateWithDuration:0.5 animations:^{
        [weakSelf.mandatoryPickupViewHeight setActive:NO];
        [weakSelf.view layoutIfNeeded];
    }];

试试改成

    [weakSelf.mandatoryPickupViewHeight setActive:NO];
    [weakSelf.view setNeedsLayout];
    [UIView animateWithDuration:0.5 animations:^{
        [weakSelf.view layoutIfNeeded];
    }];

虽然你在做的事情似乎有点晦涩难懂。如果约束被禁用，您确定自动布局有足够的约束来计算正确的高度吗？如果是这样，您确定mandatoryPickupViewHeight 约束与那些没有冲突吗？

Answer 2

这是一种将视图缩小到零高度并使其与子视图一样高的方法。

 -(void)manageViewCollapse
 {

    if(animationRunning)
   {
      return ;
   }

    animationRunning = YES;

  if(supportShown)
  {

      // Hide the view by setting its height constant to zero
      NSLayoutConstraint*full=[NSLayoutConstraint constraintWithItem:self.supportView attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0 constant:0.0];


    [self.supportView addConstraint:full];

    // retrieve the bottom constraint of the view with bottom most item and remove it
    for (NSLayoutConstraint*con in self.supportView.constraints)
    {
        if (con.firstAttribute == NSLayoutAttributeBottom && con.firstItem == self.bottomItemView)
        {

            [self.supportView removeConstraint:con];

            break;
        }


    }

        [UIView animateWithDuration:0.5 animations:^{
            [self.view layoutIfNeeded];

            }completion:^(BOOL finished){

            supportShown = NO;
            animationRunning = NO ;



            } ];


}
else
{
    // show the view first by deleting it's zero height

    for (NSLayoutConstraint*con in self.supportView.constraints)
    {
        if (con.firstAttribute == NSLayoutAttributeHeight)
        {

            [self.supportView removeConstraint:con];

            break;
        }


    }

   // hook the bottom of the view again to the bottom most item to make it have the correct height

    NSLayoutConstraint*full1=[NSLayoutConstraint constraintWithItem:self.bottomItemView attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual toItem:self.supportView attribute:NSLayoutAttributeBottom multiplier:1.0 constant:-15.0];

    full1.priority = UILayoutPriorityDefaultHigh;

    [self.supportView addConstraint:full1];


      [UIView animateWithDuration:0.5 animations:^{
            [self.view layoutIfNeeded];

            }completion:^(BOOL finished){

            supportShown = YES;
            animationRunning = NO;


            } ];





}
}