ios 添加子视图并以编程方式使用约束对其进行定位
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Adding a subview and position it with constraints programmatically
提问by Isuru
I have added a UIViewusing the IB on to the view controller. Let's call it the redView.
我已经UIView使用 IB 在视图控制器上添加了一个。我们称之为redView.
Then I have pinned its all four sides using auto layout constraints in code and when I run it, it looks like this as expected.
然后我在代码中使用自动布局约束固定了它的所有四个边，当我运行它时，它看起来像预期的那样。
Now I want to add a UILabelto this view programmatically and position it in the center using auto layout constraints.
现在我想以UILabel编程方式向这个视图添加一个并使用自动布局约束将它放置在中心。
Below is the code I have so far.
下面是我到目前为止的代码。
import UIKit
class ViewController: UIViewController {
@IBOutlet private var redView: UIView!
override func viewDidLoad() {
super.viewDidLoad()
redView.setTranslatesAutoresizingMaskIntoConstraints(false)
let leadingConstraint = NSLayoutConstraint(item: redView, attribute: .Leading, relatedBy: .Equal, toItem: view, attribute: .Leading, multiplier: 1, constant: 0)
let trailingConstraint = NSLayoutConstraint(item: redView, attribute: .Trailing, relatedBy: .Equal, toItem: view, attribute: .Trailing, multiplier: 1, constant: 0)
let topConstraint = NSLayoutConstraint(item: redView, attribute: .Top, relatedBy: .Equal, toItem: view, attribute: .Top, multiplier: 1, constant: 0)
let bottomConstraint = NSLayoutConstraint(item: redView, attribute: .Bottom, relatedBy: .Equal, toItem: view, attribute: .Bottom, multiplier: 1, constant: 0)
view.addConstraints([leadingConstraint, trailingConstraint, topConstraint, bottomConstraint])
let label = UILabel()
label.text = "Auto Layout Exercise"
redView.addSubview(label)
let xCenterConstraint = NSLayoutConstraint(item: label, attribute: .CenterX, relatedBy: .Equal, toItem: redView, attribute: .CenterX, multiplier: 1, constant: 0)
let yCenterConstraint = NSLayoutConstraint(item: label, attribute: .CenterY, relatedBy: .Equal, toItem: redView, attribute: .CenterY, multiplier: 1, constant: 0)
let leadingConstraint1 = NSLayoutConstraint(item: label, attribute: .Leading, relatedBy: .Equal, toItem: redView, attribute: .Leading, multiplier: 1, constant: 20)
let trailingConstraint1 = NSLayoutConstraint(item: label, attribute: .Trailing, relatedBy: .Equal, toItem: redView, attribute: .Trailing, multiplier: 1, constant: -20)
redView.addConstraints([xCenterConstraint, yCenterConstraint, leadingConstraint1, trailingConstraint1])
}
}
The problem is the label doesn't appear on the redView. Can anyone please tell me what I'm missing here?
问题是标签没有出现在redView. 谁能告诉我我在这里缺少什么？
Thank you.
谢谢你。
回答by Glynbeard
I'm pretty sure you need to also set:
我很确定您还需要设置：
label.setTranslatesAutoresizingMaskIntoConstraints(false)
Otherwise I don't think the constraints will apply to the label.
否则我认为这些限制不适用于标签。
回答by Nikita Kurtin
Note for Swift 2/3
Swift 2/3 的注意事项
It has changed to Boolean property: UIView.translatesAutoresizingMaskIntoConstraints
它已更改为布尔属性：UIView.translatesAutoresizingMaskIntoConstraints
Instead of it previously being:
而不是以前的：
label.setTranslatesAutoresizingMaskIntoConstraints(false)
It is now:
就是现在：
label.translatesAutoresizingMaskIntoConstraints = false
回答by jaiswal Rajan
You need to do this for each UIControl to assign NSConstraints
您需要为每个 UIControl 执行此操作以分配 NSConstraints
label.translatesAutoresizingMaskIntoConstraints = false
