以编程方式对子视图进行约束

Posted 2023-03-11

【中文标题】以编程方式对子视图进行约束

【英文标题】：Make constraints for subviews programmatically

【发布时间】：2017-07-25 12:49:19

【问题描述】：

我需要创建一个 UISlider 并将其放在现有滑块的上方。

如果我想将视图附加到其父视图，我确实知道如何为视图创建约束：

UIView *superview = view.superview;
[view setValue: [NSNumber numberWithBool: FALSE] forKey: @"translatesAutoresizingMaskIntoConstraints"];

NSLayoutConstraint *topConstraint =[NSLayoutConstraint
                                    constraintWithItem: view
                                    attribute:NSLayoutAttributeTop
                                    relatedBy:NSLayoutRelationEqual
                                    toItem: superview
                                    attribute:NSLayoutAttributeTop
                                    multiplier:1.0
                                    constant:0.0];
NSLayoutConstraint *bottomConstraint =[NSLayoutConstraint
                                       constraintWithItem: view
                                       attribute:NSLayoutAttributeBottom
                                       relatedBy:NSLayoutRelationEqual
                                       toItem: superview
                                       attribute:NSLayoutAttributeBottom
                                       multiplier:1.0
                                       constant:0.0];
NSLayoutConstraint *leadingConstraint =[NSLayoutConstraint
                                        constraintWithItem: view
                                        attribute:NSLayoutAttributeLeading
                                        relatedBy:NSLayoutRelationEqual
                                        toItem: superview
                                        attribute:NSLayoutAttributeLeading
                                        multiplier:1.0
                                        constant:0.0];
NSLayoutConstraint *trailingConstraint =[NSLayoutConstraint
                                         constraintWithItem: view
                                         attribute:NSLayoutAttributeTrailing
                                         relatedBy:NSLayoutRelationEqual
                                         toItem: superview
                                         attribute:NSLayoutAttributeTrailing
                                         multiplier:1.0
                                         constant:0.0];
NSArray *constraints = @[topConstraint, bottomConstraint, leadingConstraint, trailingConstraint];
[superview addConstraints: constraints];

但是当我需要将两个子视图附加在一起时，相同的方法不起作用。说，我有 view1 作为 superview 的子视图。它是前一段时间创建的。现在我需要另一个（view2）在superview中具有相同的定位。

类似

UIView *superview = view1.superview;

UIView *view2 = [[UIView alloc] init];
[superview addSubview: view2];

[view2 setValue: [NSNumber numberWithBool: FALSE] forKey: @"translatesAutoresizingMaskIntoConstraints"];

NSLayoutConstraint *topConstraint =[NSLayoutConstraint
                                    constraintWithItem: view1
                                    attribute:NSLayoutAttributeTop
                                    relatedBy:NSLayoutRelationEqual
                                    toItem: view2
                                    attribute:NSLayoutAttributeTop
                                    multiplier:1.0
                                    constant:0.0];
NSLayoutConstraint *bottomConstraint =[NSLayoutConstraint
                                       constraintWithItem: view1
                                       attribute:NSLayoutAttributeBottom
                                       relatedBy:NSLayoutRelationEqual
                                       toItem: view2
                                       attribute:NSLayoutAttributeBottom
                                       multiplier:1.0
                                       constant:0.0];
NSLayoutConstraint *leadingConstraint =[NSLayoutConstraint
                                        constraintWithItem: view1
                                        attribute:NSLayoutAttributeLeading
                                        relatedBy:NSLayoutRelationEqual
                                        toItem: view2
                                        attribute:NSLayoutAttributeLeading
                                        multiplier:1.0
                                        constant:0.0];
NSLayoutConstraint *trailingConstraint =[NSLayoutConstraint
                                         constraintWithItem: view1
                                         attribute:NSLayoutAttributeTrailing
                                         relatedBy:NSLayoutRelationEqual
                                         toItem: view2
                                         attribute:NSLayoutAttributeTrailing
                                         multiplier:1.0
                                         constant:0.0];
NSArray *constraints = @[topConstraint, bottomConstraint, leadingConstraint, trailingConstraint];
[superview addConstraints: constraints];

破坏一切。

【问题讨论】：

让事情变得简单......分配slider.frame = oldSlider.frame

【参考方案1】：

看起来你只是把它倒过来了......

你想限制view2 到 view1:

[NSLayoutConstraint
    constraintWithItem: view2    // <-- constrain this view
    attribute:NSLayoutAttributeTop
    relatedBy:NSLayoutRelationEqual
    toItem: view1               //  <-- to this view
    attribute:NSLayoutAttributeTop
    multiplier:1.0
    constant:0.0];