Swift 以编程方式向标签添加约束

Question

我在 for index 循环中并根据每个索引项添加标签。因为我以编程方式添加这些标签，所以我不知道如何将它们限制在设备宽度的最右侧。我在下面解释了我认为约束是如何起作用的。我的目标 = 尾随 space 到超级视图（或包含视图）常量设置为 8.

let y_align = 340 * index + 70
let x_align = self.deviceWidth - 110
var derp = UILabel(frame: CGRectMake(0, 0, 200, 21))
derp.center = CGPointMake(CGFloat(x_align), CGFloat(y_align))    
derp.textAlignment = NSTextAlignment.Right    
derp.text = json["things"][index]["thing"].string!    
self.some_view_container.addSubview(derp)

//now this is what I understand about constraints    
let xconstraint = NSLayoutConstraint(    
    item: derp, //-- the object that we want to constrain    
    attribute: NSLayoutAttribute.Trailing, //-- the attribute of the object we want to constrain    
    relatedBy: NSLayoutRelation.Equal, //-- how we want to relate THIS object to A DIFF object    
    toItem: some_view_container, //-- this is the different object we want to constrain to    
    attribute: NSLayoutAttribute.Right, //-- the attribute of the different object    
    multiplier: 1, //-- multiplier    
    constant: 8 //-- regular constant    
)

derp.addConstraint(xconstraint)

这就是我想要的人情

item: 我想约束 derp，它是 json
属性：我想限制它的尾部 space 以便它一直向右推
relatedBy：这里不知道，我不在乎它是否与任何东西相关，因为我只想要尾随 space 到 superview
toItem：我想将它推到超级视图的右侧或者它的容器是 some_view_container
attribute：这里没概念，我不关心视图容器的attribute
乘数：我只想要常量的个数，所以乘以 1
常量：我希望尾部 space 距离边缘

Answer 1

您可以使用此代码作为参考：

import UIKit

class ViewController: UIViewController {
 override func viewDidLoad() {
    super.viewDidLoad()
    addLabels()
 }

 func addLabels(){
    let deviceWidth = UIScreen.mainScreen().bounds.width
    //Here recopilate the constranins for later activation
    var constraints = [NSLayoutConstraint]()
    //Here I'm assuming that there are 5 labels
    for index in 0..<5 {
        //adjust this to spaciate labels
        let y_align = CGFloat(20 * index + 70)
        let x_align = deviceWidth - 110
        var derp = UILabel(frame: CGRectMake(0, 0, 200, 21))
        derp.center = CGPointMake(CGFloat(x_align), CGFloat(y_align))
        derp.textAlignment = NSTextAlignment.Right
        derp.text = "things \(index)"

        let xconstraint = NSLayoutConstraint(
            item: derp, //-- the object that we want to constrain
            attribute: NSLayoutAttribute.Trailing, //-- the attribute of the object we want to constrain
            relatedBy: NSLayoutRelation.Equal, //-- how we want to relate THIS object to A DIFF object
            toItem: self.view, //-- this is the different object we want to constrain to
            attribute: NSLayoutAttribute.Right, //-- the attribute of the different object
            multiplier: 1, //-- multiplier
            constant: -8 //-- (Take a look here, its a minus)
        )
        let yconstraint = NSLayoutConstraint(
            item: derp, //-- the object that we want to constrain
            attribute: NSLayoutAttribute.Top, //-- the attribute of the object we want to constrain
            relatedBy: NSLayoutRelation.Equal, //-- how we want to relate THIS object to A DIFF object
            toItem: self.view, //-- this is the different object we want to constrain to
            attribute: NSLayoutAttribute.TopMargin, //-- the attribute of the different object
            multiplier: 1, //-- multiplier
            constant: y_align //-- regular constant
        )
        //recopilate constraints created here
        constraints.append(xconstraint)
        constraints.append(yconstraint)
        derp.setTranslatesAutoresizingMaskIntoConstraints(false)
        //add them to the desired control
        self.view.addSubview(derp)
    }
    //This will tell iOS to use your constraint
    NSLayoutConstraint.activateConstraints(constraints)
 }
}

Answer 2

对于 swift 3.0

func addLabels(){
    let deviceWidth = UIScreen.main.bounds.width
    //Here recopilate the constranins for later activation
    var constraints = [NSLayoutConstraint]()
    //Here I'm assuming that there are 5 labels
    for index in 0..<5 {
        //adjust this to spaciate labels
        let y_align = CGFloat(20 * index + 70)
        let x_align = deviceWidth - 110
        var derp = UILabel(frame: CGRect(x: 0, y: 0, width: 200, height: 100))
        derp.center = CGPoint(x:CGFloat(x_align), y:CGFloat(y_align))

        derp.textAlignment = NSTextAlignment.right
        derp.text = "things \(index)"

        let xconstraint = NSLayoutConstraint(
            item: derp, //-- the object that we want to constrain
            attribute: NSLayoutAttribute.trailing, //-- the attribute of the object we want to constrain
            relatedBy: NSLayoutRelation.equal, //-- how we want to relate THIS object to A DIFF object
            toItem: self.view, //-- this is the different object we want to constrain to
            attribute: NSLayoutAttribute.right, //-- the attribute of the different object
            multiplier: 1, //-- multiplier
            constant: -8 //-- (Take a look here, its a minus)
        )
        let yconstraint = NSLayoutConstraint(
            item: derp, //-- the object that we want to constrain
            attribute: NSLayoutAttribute.top, //-- the attribute of the object we want to constrain
            relatedBy: NSLayoutRelation.equal, //-- how we want to relate THIS object to A DIFF object
            toItem: self.view, //-- this is the different object we want to constrain to
            attribute: NSLayoutAttribute.topMargin, //-- the attribute of the different object
            multiplier: 1, //-- multiplier
            constant: y_align //-- regular constant
        )
        //recopilate constraints created here
        constraints.append(xconstraint)
        constraints.append(yconstraint)
        derp.translatesAutoresizingMaskIntoConstraints = false
        //add them to the desired control
        self.view.addSubview(derp)
    }
    //This will tell iOS to use your constraint
    NSLayoutConstraint.activate(constraints)
}

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