Ios 如何以编程方式添加标签并以编程方式使用自动布局定位标签

我正在尝试向UIScrollView添加标签。我正在添加顶部约束和前导约束。 标签没有出现

这是我的密码

   self.label = [[UILabel alloc] initWithFrame:CGRectMake(0, 0, 40, 40)];
    self.label.translatesAutoresizingMaskIntoConstraints = NO;
    self.label.backgroundColor = [UIColor clearColor];
    self.label.textAlignment = NSTextAlignmentCenter;
    self.label.textColor=[UIColor whiteColor];
    self.label.text = @"Hello";
    [self.imageCarouselScrollView addSubview:self.label];
    [self bringSubviewToFront:self.label];
    self.titleLabelTopConstraint = [NSLayoutConstraint
                                    constraintWithItem:self
                                    attribute:NSLayoutAttributeTop
                                    relatedBy:NSLayoutRelationEqual
                                    toItem:self.imageCarouselScrollView
                                    attribute:NSLayoutAttributeBottom
                                    multiplier:1.0
                                    constant:20];
    NSLayoutConstraint *titleLeadingConstraint = [NSLayoutConstraint
                                                  constraintWithItem:self
                                                  attribute:NSLayoutAttributeLeading
                                                  relatedBy:NSLayoutRelationEqual
                                                  toItem:self.imageCarouselScrollView
                                                  attribute:NSLayoutAttributeTrailing
                                                  multiplier:1.0
                                                  constant:20];
    [self addConstraints:@[self.titleLabelTopConstraint,titleLeadingConstraint]];

---

您必须在滚动视图的右侧（用于水平滚动）或底部（用于垂直滚动）包含一个约束，以便它可以推断内容大小。

我尝试注释您的代码：

    self.label = [[UILabel alloc] initWithFrame:CGRectMake(0, 0, 40, 40)]; //if 'translatesAutoresizingMaskIntoConstraints=NO' frame not work work anymore. Use CGRectZero instead
    self.label.translatesAutoresizingMaskIntoConstraints = NO;
    self.label.backgroundColor = [UIColor clearColor];
    self.label.textAlignment = NSTextAlignmentCenter;
    self.label.textColor=[UIColor whiteColor];
    self.label.text = @"Hello";
    [self.imageCarouselScrollView addSubview:self.label]; //Your self.label added on 'self.imageCarouselScrollView' but your constraints added on self
    [self bringSubviewToFront:self.label]; // ??? Why?
    self.titleLabelTopConstraint = [NSLayoutConstraint
            constraintWithItem:self
                     attribute:NSLayoutAttributeTop
                     relatedBy:NSLayoutRelationEqual
                        toItem:self.imageCarouselScrollView
                     attribute:NSLayoutAttributeBottom
                    multiplier:1.0
                      constant:20]; //it constrain means: "self view top edge equal to self.imageCarouselScrollView bottom + offset 20 "
    NSLayoutConstraint *titleLeadingConstraint = [NSLayoutConstraint
            constraintWithItem:self
                     attribute:NSLayoutAttributeLeading
                     relatedBy:NSLayoutRelationEqual
                        toItem:self.imageCarouselScrollView
                     attribute:NSLayoutAttributeTrailing
                    multiplier:1.0
                      constant:20];//it constrain means: "self view Leading edge equal to self.imageCarouselScrollView Trailing + offset 20 "
    [self addConstraints:@[self.titleLabelTopConstraint,titleLeadingConstraint]];

现在我有几个问题：

为什么要限制self.label？？因为翻译后自动调整大小gmaskintoconstraints=no，it帧等于0；你再也看不到标签了

你有两个约束，其他边呢

毫无疑问，委员会，试着使用“constraintsWithVisualFormat:options:metrics:views:”

---

您是否尝试查看

ui标签

是否在未添加约束的情况下显示？而且，不要试图搞笑。。您的视图背景色没有设置为白色，是吗？对于标签，您只有两个约束来确定其x值和y值，然后其宽度和高度将基于其内容。我还没有真正尝试过使用VisualFormat约束。@user1898829

sizeToFits

不使用自动布局，请学习

setContentHuggingPriority:forAxis:

和

SetContentCompressionResistance:forAxis: