ios - 以编程方式添加约束

Question

我正在尝试以编程方式实现以下布局:

它是一个子类的 UIView，我想在它上面放置一个固定高度(40 像素)、动态宽度(宽度是根据文本的长度计算的，所以我想这可以被认为是固定的 UILabel，而不是动态的，因为我只计算了一次)，并且距离左侧和底部正好 40 像素。

这是我的代码:

- (UIView *) initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self)
    {

    marginGeneral       = 40.0f;

    UILabel *titleLabel = [[UILabel alloc] init];
    [titleLabel setTranslatesAutoresizingMaskIntoConstraints: NO];
    titleLabel.backgroundColor  = [UIColor blackColor];
    titleLabel.textColor        = [UIColor whiteColor];
    titleLabel.text             = @"Some Text";
    [self addSubview:titleLabel];

    NSLayoutConstraint *contsTitleLeft = [NSLayoutConstraint
                                          constraintWithItem: titleLabel
                                          attribute: NSLayoutAttributeLeft
                                          relatedBy: NSLayoutRelationEqual
                                          toItem: self
                                          attribute: NSLayoutAttributeLeft
                                          multiplier: 1.0
                                          constant: marginGeneral];

    NSLayoutConstraint *contsTitleRight = [NSLayoutConstraint
                                           constraintWithItem: titleLabel
                                           attribute: NSLayoutAttributeRight
                                           relatedBy: NSLayoutRelationEqual
                                           toItem: self
                                           attribute: NSLayoutAttributeRight
                                           multiplier: 1.0
                                           constant: marginGeneral * -1.0f];

    NSLayoutConstraint *contsTitleBottom = [NSLayoutConstraint
                                            constraintWithItem: titleLabel
                                            attribute: NSLayoutAttributeBottom
                                            relatedBy: NSLayoutRelationEqual
                                            toItem: self
                                            attribute: NSLayoutAttributeBottom
                                            multiplier: 1.0
                                            constant: marginGeneral * -1.0f];

    NSLayoutConstraint *contsTitleHeight = [NSLayoutConstraint
                                            constraintWithItem: titleLabel
                                            attribute: NSLayoutAttributeHeight
                                            relatedBy: NSLayoutRelationEqual
                                            toItem: nil
                                            attribute: NSLayoutAttributeNotAnAttribute
                                            multiplier: 1.0
                                            constant: 40.0f];

    [self addConstraints:@[contsTitleLeft, contsTitleRight, contsTitleBottom]];
    [titleLabel addConstraint:contsTitleHeight];

    }

return self;
}

@end

这当然会返回各种与约束相关的警告，并且标签不会显示。

你们好心人能帮助我了解我哪里出了问题以及如何纠正吗？非常感谢!

P.s.:我不使用界面生成器，所以这不是一个选项。 :)

Answer 1

首先，您从未将 titleLabel 添加为 subview 。

其次，您需要忽略自动调整大小掩码以避免约束冲突。

第三，您正在为 View 添加高度约束，而它属于标签。

这是有效的代码:

UILabel *titleLabel = [[UILabel alloc] init];
[titleLabel setTranslatesAutoresizingMaskIntoConstraints: NO];
titleLabel.backgroundColor  = [UIColor blackColor];
titleLabel.textColor        = [UIColor whiteColor];
titleLabel.text             = @"Some Text";
[self.view addSubview: titleLabel];

NSLayoutConstraint *contsTitleLeft = [NSLayoutConstraint
                                      constraintWithItem: titleLabel
                                      attribute: NSLayoutAttributeLeft
                                      relatedBy: NSLayoutRelationEqual
                                      toItem: self
                                      attribute: NSLayoutAttributeLeft
                                      multiplier: 1.0
                                      constant: marginGeneral];

NSLayoutConstraint *contsTitleRight = [NSLayoutConstraint
                                       constraintWithItem: titleLabel
                                       attribute: NSLayoutAttributeRight
                                       relatedBy: NSLayoutRelationEqual
                                       toItem: self
                                       attribute: NSLayoutAttributeRight
                                       multiplier: 1.0
                                       constant: marginGeneral * -1.0f];

NSLayoutConstraint *contsTitleBottom = [NSLayoutConstraint
                                        constraintWithItem: titleLabel
                                        attribute: NSLayoutAttributeBottom
                                        relatedBy: NSLayoutRelationEqual
                                        toItem: self
                                        attribute: NSLayoutAttributeBottom
                                        multiplier: 1.0
                                        constant: marginGeneral * -1.0f];

NSLayoutConstraint *contsTitleHeight = [NSLayoutConstraint
                                        constraintWithItem: titleLabel
                                        attribute: NSLayoutAttributeHeight
                                        relatedBy: NSLayoutRelationEqual
                                        toItem: nil
                                        attribute: NSLayoutAttributeNotAnAttribute
                                        multiplier: 1.0
                                        constant: 40.0f];

[self addConstraints:@[contsTitleLeft, contsTitleRight, contsTitleBottom]];
[titleLabel addConstraint: contsTitleHeight];

更新:在 viewDidLoad 中添加自定义 View 到 View Controller :

CustomView *customView = [[CustomView alloc] initWithFrame: CGRectMake(0, 0, 200, 200)];
[customView setTranslatesAutoresizingMaskIntoConstraints: NO];
[customView setBackgroundColor: [UIColor greenColor]];
[self.view addSubview: customView];

NSLayoutConstraint *widthConstraint = [NSLayoutConstraint constraintWithItem: customView
                                                                       attribute: NSLayoutAttributeWidth
                                                                       relatedBy: NSLayoutRelationEqual
                                                                          toItem: nil
                                                                       attribute: NSLayoutAttributeNotAnAttribute
                                                                      multiplier:1
                                                                        constant:200];
NSLayoutConstraint *heightConstraint = [NSLayoutConstraint constraintWithItem: customView
                                                                       attribute: NSLayoutAttributeHeight
                                                                       relatedBy: NSLayoutRelationEqual
                                                                          toItem: nil
                                                                       attribute: NSLayoutAttributeNotAnAttribute
                                                                      multiplier:1
                                                                        constant:200];

[customView addConstraints: @[widthConstraint, heightConstraint]];

NSLayoutConstraint *centerHorizontallyConstraint = [NSLayoutConstraint constraintWithItem: customView
                                                                                    attribute: NSLayoutAttributeCenterX
                                                                                    relatedBy: NSLayoutRelationEqual
                                                                                       toItem: self.view
                                                                                    attribute: NSLayoutAttributeCenterX
                                                                                   multiplier: 1
                                                                                     constant: 0];

NSLayoutConstraint *centerVerticallyConstraint = [NSLayoutConstraint constraintWithItem: customView
                                                                                    attribute: NSLayoutAttributeCenterY
                                                                                    relatedBy: NSLayoutRelationEqual
                                                                                       toItem: self.view
                                                                                    attribute: NSLayoutAttributeCenterY
                                                                                   multiplier: 1
                                                                                     constant: 0];

[self.view addConstraints: @[centerHorizontallyConstraint, centerVerticallyConstraint]];