IOS以编程方式在Swift中添加约束条件

因此，我完成了Xcode中的IB并且想要在Swift中编写所有UI。IOS以编程方式在Swift中添加约束条件

所以我所做的就是：

创建一个新的UIView包含我想写的元素 -
我添加TestView到VC为让称它为“TestView”子视图。

在TestView类我已经添加的元素是这样的：

class TestView: UIView { 
     var someLabel:UILabel! 
     override init(frame: CGRect) { 
      super.init(frame: frame) 

      self.someLabel = UILabel(frame: CGRect(x: self.frame.midX, y: oneSixthHeight, width: 100, height: 22)) 
      self.someLabel.text = "test" 

      var constraints:[NSLayoutConstraint] = [] 
      self.someLabel.translatesAutoresizingMaskIntoConstraints = false 
      let rightsideAnchor:NSLayoutConstraint = NSLayoutConstraint(item: self.someLabel, attribute: .Trailing, relatedBy: .Equal, toItem: self, attribute: .Trailing, multiplier: 1, constant: 1) 

      constraints.append(rightsideAnchor) 
      NSLayoutConstraint.activateConstraints(constraints) 
     } 
}

有了这个，我期待UILabel锚定到视图的右侧。

不过，我得到这个错误：

Terminating app due to uncaught exception 'NSGenericException', reason: 'Unable to activate constraint with items > and > because they have no common ancestor.
Does the constraint reference items in different view hierarchies? That's illegal.'

我在做什么错？

来源

2016-11-28 Simon k

你在哪里添加someLabel为您的视图的子视图？您只能应用约束，并在已添加为子视图时将其激活。否则尝试会导致崩溃，你只看到 –

只有在将视图添加到视图层次结构后，才应该添加约束。从你的代码中可以清楚的看到你没有添加UILabel实例来查看。

来源

2016-11-28 08:34:53 msk

宾果:)因此，投票:) –

谢谢你！ :)添加了标签作为子视图，它都像一个魅力。 <3 –

很高兴它的工作。 – msk

更新了斯威夫特3约束

import UIKit 

class ViewController: UIViewController { 

let redView: UIView = { 

    let view = UIView() 
    view.translatesAutoresizingMaskIntoConstraints = false 
    view.backgroundColor = .red 
    return view 
}() 

override func viewDidLoad() { 
    super.viewDidLoad() 

    setupViews() 
    setupAutoLayout() 
} 

func setupViews() { 

    view.backgroundColor = .white 
    view.addSubview(redView) 
} 

func setupAutoLayout() { 

    // Available from iOS 9 commonly known as Anchoring System for AutoLayout... 
    redView.leftAnchor.constraint(equalTo: view.leftAnchor, constant: 20).isActive = true 
    redView.rightAnchor.constraint(equalTo: view.rightAnchor, constant: -20).isActive = true 

    redView.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true 
    redView.heightAnchor.constraint(equalToConstant: 300).isActive = true 

    // You can also modified above last two lines as follows by commenting above & uncommenting below lines... 
    // redView.topAnchor.constraint(equalTo: view.topAnchor, constant: 20).isActive = true 
    // redView.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true 
} 
}

类型：

/* 
// regular use 
1.leftAnchor 
2.rightAnchor 
3.topAnchor 
// intermediate use 
4.widthAnchor 
5.heightAnchor 
6.bottomAnchor 
7.centerXAnchor 
8.centerYAnchor 
// rare use 
9.leadingAnchor 
10.trailingAnchor 
etc. (note: very project to project) 
*/

来源

2017-07-14 09:05:40 iajmeri43

IOS以编程方式在Swift中添加约束条件

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