如何将自动布局约束添加到表视图标题视图中的多行 UILabel 视图

Question

我整天都在寻找这个问题的解决方案。我正在尝试让我的 UILabels 根据tableViewHeaderView内文本的长度自动调整自己的大小。通常，将我的 UILabels 放在 UIView 中，我会为 UILeu 设置顶部、前导和尾随约束，它会像我想要的那样工作。但是，我无法在tableViewHeaderView内工作.我能够设置顶部和前导约束，但我的尾随约束似乎不起作用。文本超出屏幕宽度。

将 preferredMaxLayoutWidth 属性设置为数字可以解决问题，但我不想对其进行硬编码。

如果我错了，请纠正我，但是设置前导和尾随约束应该能够为我提供视图的宽度，不是吗？然后我可以用该值设置preferredMaxLayoutWidth。但该值是 2403，比屏幕宽度长得多。

还有其他人经历过吗？

#import "CustomTableViewHeader.h"
@implementation ReplyHeader{
    UILabel *questionLabel;
}

questionLabel = [[UILabel alloc]init];
            questionLabel.text = @"SAMPLE TEXT: I had a question about how I can be a better human being using your method. I belive it is an integral part of what it means to be a human so I want to learn more if you are able give more details about it. I also found that what you said about the dogs out there is very cool and would love to learn more about that.";
            questionLabel.font = [UIFont fontWithName:@"AvenirNext-Regular" size:17];
        questionLabel.lineBreakMode = NSLineBreakByWordWrapping;
        questionLabel.numberOfLines = 0;
        questionLabel.translatesAutoresizingMaskIntoConstraints = NO;
        [self addSubview:questionLabel];

约束

  [self addConstraint:[NSLayoutConstraint constraintWithItem:questionLabel attribute:NSLayoutAttributeLeading relatedBy:NSLayoutRelationEqual toItem:self attribute:NSLayoutAttributeLeading multiplier:1.0f constant:5.0f]];
        [self addConstraint:[NSLayoutConstraint constraintWithItem:questionLabel attribute:NSLayoutAttributeTrailing relatedBy:NSLayoutRelationEqual toItem:self attribute:NSLayoutAttributeTrailing multiplier:1.0f constant:-5.0f]];
            [self addConstraint:[NSLayoutConstraint constraintWithItem:questionLabel attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:self attribute:NSLayoutAttributeTop multiplier:1.0f constant:10]];
        [self addConstraint:[NSLayoutConstraint constraintWithItem:questionLabel attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual toItem:self attribute:NSLayoutAttributeBottom multiplier:1.0f constant:-10]];

更新视图

- (void)viewDidLayoutSubviews
{
    questionLabel.preferredMaxLayoutWidth = questionLabel.frame.size.width;
    [self layoutIfNeeded];
}

Answer 1

UITableView与AutoLayout不相处。页眉和页脚都继承了这个问题。您可能已经知道，UITableViews是花哨的UIScrollViews。如果您曾经尝试过使用滚动视图，许多元素和自动布局，则必须知道它不能很好地工作。它滞后。这就是UITableView重用单元格的原因。它提高了性能，并且他们不使用自动布局。

你应该尝试类似的东西

 // with this you will get the most compressed size for your view if the constraints properly define it's size
 CGFloat height = [footer systemLayoutSizeFittingSize:UILayoutFittingCompressedSize].height;
 footer = CGRectMake(CGRectGetMinX(view.frame), CGRectGetMinY(footer.frame), CGRectGetWidth(footer.bounds), height);
 // This will tell the layout engine to ignore the view and not try to resize it
 view.autoresizingMask = UIViewAutoresizingNone; 
 self.tableView.tableFooterView = footer;