程序化自动布局问题 iOS 8.0

Question

在 iOS 8.0 中看到一些关于自动布局行为的奇怪行为，并正在寻找有关如何解决此问题的任何提示或帮助。我有一个 UIView 包含另一个 UIView 作为包含两个标签的子视图。这些标签的约束以编程方式添加如下：

    //StreamCaptionTextView.m
    - (void)updateConstraints
    {
      NSDictionary *views = @{
                              @"title"   : self.titleLabel,
                              @"desc"    : self.descLabel
                              };

      NSDictionary *metrics = @{
                                @"top"    : @0,
                                @"middle" : @(-2)
                                };

      [self addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-0-[title]-0-|" options:0 metrics:metrics views:views]];
      [self addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-0-[desc]-0-|" options:0 metrics:metrics views:views]];
      [self addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|-top-[title]-middle-[desc(==title)]" options:0 metrics:metrics views:views]];

      [super updateConstraints];
    }

这个 labelView 的父视图也为 labelView 设置了约束。

//StreamCaptionView which contains the StreamCaptionTextView
- (void)updateConstraints
{
  [self removeConstraints:self.constraints];

  NSMutableDictionary *views = [[NSMutableDictionary alloc] initWithDictionary:@{
                                                                                 @"image"    : self.profileImageBtn,
                                                                                 @"leftView" : self.leftText
                                                                                 }];
  NSDictionary *metrics = @{
                            @"top"        : @6,
                            @"left"       : @8,
                            @"imageSize"  : @24,
                            @"marginText" : @10,
                            @"maxWidth"   : @120
                            };

  [self addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|-top-[image(imageSize)]" options:0 metrics:metrics views:views]];
  [self addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|-top-[leftView]-top-|" options:0 metrics:metrics views:views]];

  if(self.rightAcessoryView)
  {
    views[@"rightView"] = self.rightAcessoryView ;
    [self addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-left-[image(imageSize)]-2-[leftView]-10-[rightView(maxWidth)]-10-|" options:0 metrics:metrics views:views]];
    [self addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|-top-[rightView]-top-|" options:0 metrics:metrics views:views]];
  }
  else
  {
    [self addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-marginText-[image(imageSize)]-2-[leftView]-marginText-|" options:0 metrics:metrics views:views]];
  }

  [super updateConstraints];
}


//This is the View that contains the captionView
- (void)setVo:(RecordingStreamItemVO *)vo
    {
      _vo = vo;

      __weak RecordingDetailVideoView *_self = self;

      self.captionView.title            = vo.user.screenname;
      self.captionView.subTitle         = vo.title;
      self.captionView.profileImageURL  = vo.user.pictureURL;

      //Here, the captionView is the rectangular blur, inside of the
      //captionView is another UIView that contains the UILabels.

    }

由于某种原因，只有在 iOS 8.0 上，标签没有在 labelView 中正确呈现。这适用于 iOS 8.1 和 7.1 等。我尝试使用 [self.labelView setNeedsUpdateConstraints] 使约束无效，但这似乎没有 解决问题。我已经用谷歌搜索了很多，我看到其他人在 iOS 8.0 上遇到了 autoLayout 问题，但想验证这是否是 iOS 问题以及我可以实施的任何潜在解决方法。

//这里有一些照片展示了它在 Xcode 可视化调试器中的样子

//第一张照片在iOS 8.1上运行正常

//这张照片是在 iOS 8.0 上，似乎忽略了约束。

//ios 8.0

layer = <CALayer: 0x17396c90>>
   |    |    |    |    |    |    |    |    |    | <StreamCaptionView: 0x15f1fe10; frame = (0 146; 320 35); layer = <CALayer: 0x15f2b3e0>>
   |    |    |    |    |    |    |    |    |    |    | <UIButton: 0x15fcc240; frame = (10 6; 24 24); opaque = NO; layer = <CALayer: 0x15fcc340>>
   |    |    |    |    |    |    |    |    |    |    |    | <UIImageView: 0x1700d1c0; frame = (0 0; 24 24); clipsToBounds = YES; opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0x1700d240>>
   |    |    |    |    |    |    |    |    |    |    | <StreamCaptionTextView: 0x15fcc410; frame = (36 6; 274 23); layer = <CALayer: 0x15f2f620>>
   |    |    |    |    |    |    |    |    |    |    |    | <MarqueeLabel: 0x15f2f650; baseClass = UILabel; frame = (0 0; 274 13.5); text = 'test1'; clipsToBounds = YES; userInteractionEnabled = NO; layer = <_UILabelLayer: 0x15f200b0>>
   |    |    |    |    |    |    |    |    |    |    |    |    | <UILabel: 0x17378d20; frame = (0 0; 26 0); text = 'test1'; userInteractionEnabled = NO; tag = 700; animations = { position=<CAKeyframeAnimation: 0x173b8960>; }; layer = <_UILabelLayer: 0x17378de0>>
   |    |    |    |    |    |    |    |    |    |    |    |    | <UILabel: 0x173906b0; frame = (45 0; 22 0); text = 'test1'; userInteractionEnabled = NO; tag = 701; animations = { position=<CAKeyframeAnimation: 0x173b8a60>; }; layer = <_UILabelLayer: 0x17390770>>
   |    |    |    |    |    |    |    |    |    |    |    | <MarqueeLabel: 0x17390c40; baseClass = UILabel; frame = (0 11.5; 274 13.5); text = 'Test'; clipsToBounds = YES; userInteractionEnabled = NO; layer = <_UILabelLayer: 0x17390d60>>
   |    |    |    |    |    |    |    |    |    |    |    |    | <UILabel: 0x17390940; frame = (0 0; 17 0); text = 'Test'; userInteractionEnabled = NO; tag = 700; animations = { position=<CAKeyframeAnimation: 0x173b93a0>; }; layer = <_UILabelLayer: 0x17390a00>>
   |    |    |    |    |    |    |    |    |    |    |    |    | <UILabel: 0x173a1640; frame = (82 0; 48 0); text = 'Test'; userInteractionEnabled = NO; tag = 701; animations = { position=<CAKeyframeAnimation: 0x173b94a0>; }; layer = <_UILabelLayer: 0x173a1700>>
   |    |    |    |    |    |    |    |    | <_UITableViewCellSeparatorView: 0x173ae010; frame = (15 179.5; 305 0.5); layer = <CALayer: 0x173ad1d0>>
   |    |    |    |    |    |    |    | <TimePublishedDetailView: 0x173a1d60; frame = (238.5 20; 71.5 11); layer = <CALayer: 0x173a1ef0>>
   |    |    |    |    |    |    |    |    | <UIImageView: 0x173a21e0; frame = (0 0; 9 9); opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0x173a2260>>
   |    |    |    |    |    |    |    |    | <UILabel: 0x173a85d0; frame = (16 -2; 55.5 13.5); text = '5 hours ago'; userInteractionEnabled = NO; layer = <_UILabelLayer: 0x173a8550>>

更新：

我实际上在父视图控制器中通过一个非常简单的修复解决了这个问题。

- (void)viewDidLoad
{
  [super viewDidLoad];
  // Do any additional setup after loading the view.

  [self.view addSubview:self.detailsView];
  [self.view setNeedsUpdateConstraints];
}

- (void)viewWillAppear:(BOOL)animated
{
  [super viewWillAppear:animated];
  [self loadDetails];

  [self.view layoutIfNeeded]; //This fixed the iOS 8.0 problem

}

//In my case the self.detailsView property contains the view hierarchy which 
//contains the UILabels that weren't being rendered properly way down
//in the view hierarchy. calling layoutIfNeeded fixes this problem for me. 

Answer 1

首先，您需要确切地知道发生了什么。在方便的时候暂停应用程序，然后在控制台中输入以下命令：

po [[UIWindow keyWindow] recursiveDescription]

如果这对您没有帮助，请至少尝试将其发布在此处作为我们的参考。

通常进行手动布局会导致布局受到不足或过度约束，而 Interface Builder 会对此发出警告。对我来说，没有更广泛的调试信息，我仍然有点盲目。

现在我有了这些日志，我注意到以下几行：

   |    |    |    |    |    |    |    |    |    |    |    |    | <UILabel: 0x17378d20; frame = (0 0; 26 0); text = 'test1'; userInteractionEnabled = NO; tag = 700; animations = { position=<CAKeyframeAnimation: 0x173b8960>; }; layer = <_UILabelLayer: 0x17378de0>>
   |    |    |    |    |    |    |    |    |    |    |    |    | <UILabel: 0x173906b0; frame = (45 0; 22 0); text = 'test1'; userInteractionEnabled = NO; tag = 701; animations = { position=<CAKeyframeAnimation: 0x173b8a60>; }; layer = <_UILabelLayer: 0x17390770>>

所以所有标签似乎都没有高度。

这条线可能是关闭的：

@"V:|-top-[title]-middle-[desc(==title)]"

它似乎没有点击到底部，所以它不能给出标题高度或描述？尝试做这样的事情：

@"V:|-top-[title]-middle-[desc(==title)]-|"

或者给出一个最小高度：

@"V:|-top-[title(>=10)]-middle-[desc(==title)]"