简单封装系统LayoutConstraint，实现类似Mason

GitHub上的代码👉，后续有时间会有更新。>>>GRLayout demo

• 使用

import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        let testView = UIView()
        testView.backgroundColor = .yellow
        view.addSubview(testView)
        testView.gr_top.equal(view.gr_top).offset(100.0)
        testView.gr_left.equal(view.gr_left).offset(10.0)
        testView.gr_right.equal(view.gr_right).offset(-10.0)
        testView.gr_bottom.equal(view.gr_bottom).offset(-100)
//        testView.gr_height.greaterThanOrEqual(200.0)
    }
}

• 设计

第一反应想到的是给UIView做一个extension，让它及其子类都带有特定都属性，可以调用方法去设置，修改约束。
所以这里设计了几个属性，用于约束设置。

• gr_top
• gr_bottom
• gr_left
• gr_right
• gr_height
• gr_width

在UIView+Extension.swift 文件中，代码如下：

import UIKit

extension UIView {
    
    var gr_top: GRLayoutY {
        get {
            translatesAutoresizingMaskIntoConstraints = false
            return GRLayoutY.create(anchor: topAnchor)
        }
    }

    var gr_bottom: GRLayoutY {
        get {
            translatesAutoresizingMaskIntoConstraints = false
            return GRLayoutY.create(anchor: bottomAnchor)
        }
    }

    var gr_left: GRLayoutX {
        get {
            translatesAutoresizingMaskIntoConstraints = false
            return GRLayoutX.create(anchor: leftAnchor)
        }
    }

    var gr_right: GRLayoutX {
        get {
            translatesAutoresizingMaskIntoConstraints = false
            return GRLayoutX.create(anchor: rightAnchor)
        }
    }

    var gr_height: GRLayoutDimension {
        get {
            translatesAutoresizingMaskIntoConstraints = false
            return GRLayoutDimension.create(anchor: heightAnchor)
        }
    }

    var gr_width: GRLayoutDimension {
        get {
            translatesAutoresizingMaskIntoConstraints = false
            return GRLayoutDimension.create(anchor: widthAnchor)
        }
    }
}

• 添加方法实现，实现像Masonry链式编程的约束方法。(如果不明白什么是链式编程，可以看这里)

class GRLayoutY: NSObject {
    open var constant: CGFloat = 0.0 {
        didSet {
            curLayoutConstraint.constant = constant
        }
    }
    
    open var priority: Int = 1000 {
        didSet {
            curLayoutConstraint.priority = UILayoutPriority(rawValue: Float(priority))
        }
    }
    
    private var curLayoutConstraint = NSLayoutConstraint()
    private var curAnchor = NSLayoutYAxisAnchor()
    
    open class func create(anchor: NSLayoutYAxisAnchor) -> GRLayoutY {
        let grabin = GRLayoutY()
        grabin.curAnchor = anchor
        return grabin
    }
    
    @discardableResult open func equal(_ other: GRLayoutY) -> GRLayoutY {
        curLayoutConstraint = curAnchor.constraint(equalTo: other.curAnchor)
        curLayoutConstraint.isActive = true
        return self
    }
    
    @discardableResult open func offset(_ offSet: CGFloat) -> GRLayoutY {
        curLayoutConstraint.constant = offSet
        return self
    }
}

class GRLayoutX: NSObject {
    open var constant: CGFloat = 0.0 {
        didSet {
            curLayoutConstraint.constant = constant
        }
    }
    open var priority: Int = 1000 {
        didSet {
            curLayoutConstraint.priority = UILayoutPriority(rawValue: Float(priority))
        }
    }
    private var curLayoutConstraint = NSLayoutConstraint()
    private var curAnchor = NSLayoutXAxisAnchor()
    
    open class func create(anchor: NSLayoutXAxisAnchor) -> GRLayoutX {
        let grabin = GRLayoutX()
        grabin.curAnchor = anchor
        return grabin
    }
    
    @discardableResult open func equal(_ other: GRLayoutX) -> GRLayoutX {
        curLayoutConstraint = curAnchor.constraint(equalTo: other.curAnchor)
        curLayoutConstraint.isActive = true
        return self
    }
    
    @discardableResult open func offset(_ offSet: CGFloat) -> GRLayoutX {
        curLayoutConstraint.constant = offSet
        return self
    }
}

class GRLayoutDimension: NSObject {
    open var constant: CGFloat = 0.0 {
        didSet {
            curLayoutConstraint.constant = constant
        }
    }
    open var priority: Int = 1000 {
        didSet {
            curLayoutConstraint.priority = UILayoutPriority(rawValue: Float(priority))
        }
    }
    private var curLayoutConstraint = NSLayoutConstraint()
    private var curAnchor = NSLayoutDimension()
    
    open class func create(anchor: NSLayoutDimension) -> GRLayoutDimension {
        let grabin = GRLayoutDimension()
        grabin.curAnchor = anchor
        return grabin
    }
    
    @discardableResult open func equal(_ other: GRLayoutDimension, multiplier: CGFloat = 1) -> GRLayoutDimension {
        curLayoutConstraint = curAnchor.constraint(equalTo: other.curAnchor, multiplier: multiplier)
        curLayoutConstraint.isActive = true
        return self
    }
    
    @discardableResult open func equal(_ equalToConstant: CGFloat) -> GRLayoutDimension {
        curLayoutConstraint = curAnchor.constraint(equalToConstant: equalToConstant)
        curLayoutConstraint.isActive = true
        return self
    }
    
    @discardableResult open func greaterThanOrEqual(_ toConstant: CGFloat) -> GRLayoutDimension {
        curLayoutConstraint = curAnchor.constraint(greaterThanOrEqualToConstant: toConstant)
        curLayoutConstraint.isActive = true
        return self
    }
    
    @discardableResult open func lessThanOrEqual(_ toConstant: CGFloat) -> GRLayoutDimension {
        curLayoutConstraint = curAnchor.constraint(lessThanOrEqualToConstant: toConstant)
        curLayoutConstraint.isActive = true
        return self
    }
    
    @discardableResult open func offset(_ offSet: CGFloat) -> GRLayoutDimension {
        curLayoutConstraint.constant = offSet
        return self
    }
}

• Tips

让Xcode不报返回值使用警告，可以在带返回值的方法前加 @discardableResult