使用自动布局调整同级视图大小时，重新定位带有子视图的UIView不起作用

Question

我有两个视图，我试图用自动布局调整大小/重新定位。

我设置了以下约束：

红色视图：

• 超级视图的顶部空间：0
• 落后和领先空间到超级视图：0
• 高度等于：100

蓝色视图：

• 顶部空间到红色视图：0
• 落后和领先空间到超级视图：0
• 高度等于：100

两个视图都是self.view的子视图。蓝色视图有一个UILabel作为子视图（屏幕截图中未显示）。我想做的是更改红色视图的大小（带有动画），并让蓝色视图跟随该大小更改：

- (IBAction)resizeButtonPressed:(UIButton*)sender
{
    [UIView animateWithDuration:0.25 animations:^{
        if (sender.selected) {
            self.redViewHeightConstraint.constant = 100; // collapse
        }
        else {
            self.redViewHeightConstraint.constant = 200; // expand
        }
        [self.view layoutIfNeeded];
    }];

    sender.selected = !sender.selected;
}

动画生效，红色视图的大小发生变化。但是，蓝色视图永远不会改变位置，即使它对红色视图的底部有约束。

我尝试过添加 [self.blueView 布局需要] 甚至 [自我.视图集需要更新约束] 和 [自我.blueView 设置需要更新约束]，但这没有任何区别。

奇怪的是，如果我从蓝色视图中删除标签，一切都会按预期运行。只要我再次添加它，蓝色视图就保持不变。标签是否有任何约束没有区别。

Answer 1

我也遇到过同样的问题。我通过将标签的帧保存在动画块之前（CGRect frame=self.label.frame；），并在动画块中再次设置标签的帧（

Answer 2

这是一个完整的实现：

@interface ViewController ()

@property(nonatomic, strong) NSLayoutConstraint* redViewHeightConstraint;

@end

@implementation ViewController


-  (void)viewDidLoad
{
    [super viewDidLoad];

    UIView* redView = [[UIView alloc] init];
    UIView* blueView = [[UIView alloc] init];

    redView.translatesAutoresizingMaskIntoConstraints = NO;
    blueView.translatesAutoresizingMaskIntoConstraints = NO;

    redView.backgroundColor = [UIColor redColor];
    blueView.backgroundColor = [UIColor blueColor];

    NSDictionary* views = NSDictionaryOfVariableBindings(redView, blueView);

    [self.view addSubview:redView];
    [self.view addSubview:blueView];

    [self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|[redView]|"
                                                                      options:0
                                                                      metrics:nil
                                                                        views:views]];
    [self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|[blueView]|"
                                                                      options:0
                                                                      metrics:nil
                                                                        views:views]];

    [self.view addConstraint:[NSLayoutConstraint constraintWithItem:redView
                                                          attribute:NSLayoutAttributeTop
                                                          relatedBy:NSLayoutRelationEqual
                                                             toItem:self.view
                                                          attribute:NSLayoutAttributeTop
                                                         multiplier:1
                                                           constant:0]];

    self.redViewHeightConstraint = [NSLayoutConstraint constraintWithItem:redView
                                                                attribute:NSLayoutAttributeHeight
                                                                relatedBy:NSLayoutRelationEqual
                                                                   toItem:nil
                                                                attribute:NSLayoutAttributeNotAnAttribute
                                                               multiplier:0
                                                                 constant:100];

    [self.view addConstraint:self.redViewHeightConstraint];


    [self.view addConstraint:[NSLayoutConstraint constraintWithItem:blueView
                                                          attribute:NSLayoutAttributeTop
                                                          relatedBy:NSLayoutRelationEqual
                                                             toItem:redView
                                                          attribute:NSLayoutAttributeBottom
                                                         multiplier:1
                                                           constant:0]];

    [self.view addConstraint:[NSLayoutConstraint constraintWithItem:blueView
                                                          attribute:NSLayoutAttributeHeight
                                                          relatedBy:NSLayoutRelationEqual
                                                             toItem:nil
                                                          attribute:NSLayoutAttributeNotAnAttribute
                                                         multiplier:0
                                                           constant:100]];

    UILabel* label = [[UILabel alloc] init];
    label.text = @"label";
    label.translatesAutoresizingMaskIntoConstraints = NO;
    [blueView addSubview:label];

    [blueView addConstraint:[NSLayoutConstraint constraintWithItem:label
                                                          attribute:NSLayoutAttributeCenterX
                                                          relatedBy:NSLayoutRelationEqual
                                                             toItem:blueView
                                                          attribute:NSLayoutAttributeCenterX
                                                         multiplier:1
                                                           constant:0]];

    [blueView addConstraint:[NSLayoutConstraint constraintWithItem:label
                                                         attribute:NSLayoutAttributeCenterY
                                                         relatedBy:NSLayoutRelationEqual
                                                            toItem:blueView
                                                         attribute:NSLayoutAttributeCenterY
                                                        multiplier:1
                                                          constant:0]];

    UIButton *button = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    [button addTarget:self
               action:@selector(resizeButtonPressed:)
     forControlEvents:UIControlEventTouchUpInside];
    [button setTitle:@"Expand" forState:UIControlStateNormal];
    [button setTitle:@"Collapse" forState:UIControlStateSelected];
    button.translatesAutoresizingMaskIntoConstraints = NO;
    [self.view addSubview:button];

    [self.view addConstraint:[NSLayoutConstraint constraintWithItem:button
                                                          attribute:NSLayoutAttributeTop
                                                          relatedBy:NSLayoutRelationEqual
                                                             toItem:blueView
                                                          attribute:NSLayoutAttributeBottom
                                                         multiplier:1
                                                           constant:30]];

    [self.view addConstraint:[NSLayoutConstraint constraintWithItem:button
                                                          attribute:NSLayoutAttributeCenterX
                                                          relatedBy:NSLayoutRelationEqual
                                                             toItem:self.view
                                                          attribute:NSLayoutAttributeCenterX
                                                         multiplier:1
                                                           constant:0]];



}

- (IBAction)resizeButtonPressed:(UIButton*)sender
{
    [UIView animateWithDuration:0.25 animations:^{
        if (sender.selected) {
            self.redViewHeightConstraint.constant = 100; // collapse
        }
        else {
            self.redViewHeightConstraint.constant = 200; // expand
        }
        [self.view layoutIfNeeded];
    }];

    sender.selected = !sender.selected;
}

@end