iOS - 带约束的多行 UILabel 高度

Question

我正在尝试创建一个可重用的消息UIView 子类，该子类根据其UILabel 中的文本调整其高度。这个答案说它不能完成。真的是这样吗？ iOS message cell width/height using auto layout

我的问题是 UILabel 的 CGFrame 的高度太大。 （UILabel 的背景颜色为绿色。）

这是我的代码（顺便说一下，[autolayoutView] 将 translatesAutoresizingMaskIntoConstraints 设置为 NO）：

SSLStickyView *stickyView = [[SSLStickyView alloc] initWithText:@"Try keeping a steady beat to help me get past the notes! Press the bass drum to jump!"];

SSLStickyView.m

- (instancetype)initWithText:(NSString *)text
{
    self = [super initWithFrame:CGRectZero];
    if (self)
    {

        _stickyImageView = [UIImageView autoLayoutView];
        _stickyImageView.backgroundColor = [UIColor blueColor];
        _stickyImageView.image = [UIImage imageNamed:@"element_sticky"];
        [self addSubview:_stickyImageView];

        float padding = 5;
        NSMutableAttributedString *attributedText =
        [[NSMutableAttributedString alloc]
         initWithString:text
         attributes:@
         {
         NSFontAttributeName: [UIFont boldSystemFontOfSize:30],
         NSForegroundColorAttributeName: [UIColor purpleColor]
         }];

        UILabel *textLabel = [UILabel autoLayoutView];
        textLabel.preferredMaxLayoutWidth = 50;
        textLabel.attributedText = attributedText;
        textLabel.numberOfLines = 0; // unlimited number of lines
        textLabel.lineBreakMode = NSLineBreakByWordWrapping;
        textLabel.backgroundColor = [UIColor greenColor];

        [_stickyImageView addSubview:textLabel];

        NSLayoutConstraint *stickyWidthPin =
        [NSLayoutConstraint constraintWithItem:_stickyImageView
                                     attribute:NSLayoutAttributeWidth
                                     relatedBy:NSLayoutRelationEqual
                                        toItem:textLabel
                                     attribute:NSLayoutAttributeWidth
                                    multiplier:1
                                      constant:padding * 2];
        NSLayoutConstraint *stickyHeightPin =
        [NSLayoutConstraint constraintWithItem:_stickyImageView
                                     attribute:NSLayoutAttributeHeight
                                     relatedBy:NSLayoutRelationEqual
                                        toItem:textLabel
                                     attribute:NSLayoutAttributeHeight
                                    multiplier:1
                                      constant:0];
        NSLayoutConstraint *stickyTextLabelTop =
        [NSLayoutConstraint constraintWithItem:_stickyImageView
                                     attribute:NSLayoutAttributeTop
                                     relatedBy:NSLayoutRelationEqual
                                        toItem:textLabel
                                     attribute:NSLayoutAttributeTop
                                    multiplier:1
                                      constant:0];
        NSLayoutConstraint *stickyTextLeftPin = [NSLayoutConstraint constraintWithItem:_stickyImageView
                                                                            attribute:NSLayoutAttributeLeft
                                                                            relatedBy:NSLayoutRelationEqual
                                                                               toItem:textLabel
                                                                            attribute:NSLayoutAttributeLeft
                                                                           multiplier:1
                                                                             constant:-padding * 2];
        NSDictionary *views = NSDictionaryOfVariableBindings(_stickyImageView, textLabel);
        [self addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"|[_stickyImageView]" options:0 metrics:nil views:views]];
        [self addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|[_stickyImageView]" options:0 metrics:nil views:views]];
        [self addConstraints:@[stickyWidthPin, stickyHeightPin, stickyTextLeftPin, stickyTextLabelTop]];
        self.backgroundColor = [UIColor whiteColor];

    }

    return self;
}

Answer 1

让您的 superview 了解其内容大小的变化，并相应地调整 superview 的宽度和高度。由于如何做到这一点可能不是很明显，我提供了一个 UIView 子类，它将根据其内容（一个 UILabel）调整自身大小。

注意：仅向 ReusableMessageView 添加会影响其在其父视图中的位置的约束。 ReusableMessageView 将根据消息调整其宽度/高度。

@interface ReusableMessageView : UIView
-(instancetype)initWithMessage:(NSString *)message preferredWidth:(CGFloat)width;
-(void)setMessage:(NSString *)message;
@end

@implementation ReusableMessageView {
    UILabel *_label;
}

-(instancetype)initWithMessage:(NSString *)message preferredWidth:(CGFloat)width {
    if (self = [super init]) {
        self.translatesAutoresizingMaskIntoConstraints = NO;
        //setup label
        _label = [UILabel new];
        _label.translatesAutoresizingMaskIntoConstraints = NO;
        _label.text = message;
        _label.preferredMaxLayoutWidth = width;
        _label.numberOfLines = 0;
        [self addSubview:_label];
    }
    return self;
}

-(void)layoutSubviews {
    [super layoutSubviews];
    // remove all previously added constraints
    [self removeConstraints:self.constraints];

    CGFloat width = _label.bounds.size.width;
    CGFloat height = _label.bounds.size.height;

    NSLayoutConstraint *c1,*c2,*c3,*c4;
    // set the view's width/height to be equal to the label's width/height
    c1 = [NSLayoutConstraint constraintWithItem:self attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0 constant:width];
    c2 = [NSLayoutConstraint constraintWithItem:self attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0 constant:height];
    // center the label
    c3 = [NSLayoutConstraint constraintWithItem:_label attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:self attribute:NSLayoutAttributeCenterX multiplier:1.0 constant:0.0];
    c4 = [NSLayoutConstraint constraintWithItem:_label attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:self attribute:NSLayoutAttributeCenterY multiplier:1.0 constant:0.0];
    // add all constraints
    [self addConstraints:@[c1,c2,c3,c4]];
}

-(void)setMessage:(NSString *)message {
    _label.text = message;
    // once the message changes, the constraints need to be adjusted
    [self setNeedsLayout];
}
@end

这可以通过重用现有约束并仅更改每个约束的“常量”属性来改进。如果您这样做，您甚至可以为更改设置动画。

这是一个在 viewController 的 viewDidLoad 方法中使用的示例：

ReusableMessageView *view = [[ReusableMessageView alloc]initWithMessage:@"This is the first message that is rather long in order to exaggerate the change in size" preferredWidth:50.0];
[self.view addSubview:view];
[self.view addConstraint:[NSLayoutConstraint constraintWithItem:view attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterX multiplier:1.0 constant:0.0]];
[self.view addConstraint:[NSLayoutConstraint constraintWithItem:view attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterY multiplier:1.0 constant:0.0]];
// demonstrate the change in size
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(2.0 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
    [view setMessage:@"This is the second message"];
});

Answer 2

当然可以，但不能没有代码。视图不会根据其内部内容的约束和大小自动变小。这不是自动布局的行为方式。

您可以根据其中的约束和大小（使用systemLayoutFittingSize）确定某物需要的大小，并且您可以设置该东西代码中的那个大小。但这不会通过某种魔法发生。