SnapKit 源码阅读笔记

• Basic Information
• Note
  • Constraint.swift
  • ConstraintPriority.swift
  • ConstraintInsets.swift
  • ConstraintAttributes.swift
  • Targets
  • Maker

Basic Information

• Name:SnapKit
• Site:https://github.com/SnapKit/SnapKit
• Version:4.0.0
• Introduce: https://github.com/SnapKit/SnapKit/blob/develop/README.md

Note

Constraint.swift

class Constraint

• Property
  • internal let sourceLocation: (String, UInt)
  • internal let label: String?
  • private let from: ConstraintItem
  • private let to: ConstraintItem
  • private let relation: ConstraintRelation
  • private let multiplier: ConstraintMultiplierTarget
  • private var constant: ConstraintConstantTarget
  • private var priority: ConstraintPriorityTarget
  • public var layoutConstraints: [LayoutConstraint]
  • public var isActive: Bool {get}

一个实例对象由一个maker语句生成.

    view1.snp.makeConstraints { (maker) in
        maker.edges.equalToSuperview()
    }

生成一个Constraint对象,但是layoutConstraints有4个约束.

    view1.snp.makeConstraints { (maker) in
        maker.top.equalToSuperview()
        maker.left.equalToSuperview()
        maker.bottom.equalToSuperview()
        maker.right.equalToSuperview()
    }

生成4个Constraint对象,每个对象中分别有一个约束.所有两种写法是相同的.
但是第一种写法共用一个multiplier,constant,priority.如果这三个值不相同的话就需要使用第二种写法了.

let layoutFromAttributes = self.from.attributes.layoutAttributes
for layoutFromAttribute in layoutFromAttributes {
        // ... 省略部分代码
        // create layout constraint
        let layoutConstraint = LayoutConstraint(
            item: layoutFrom,
            attribute: layoutFromAttribute,
            relatedBy: layoutRelation,
            toItem: layoutTo,
            attribute: layoutToAttribute,
            multiplier: self.multiplier.constraintMultiplierTargetValue,
            constant: layoutConstant
        )

        // append
        self.layoutConstraints.append(layoutConstraint)
    }

每个Constraint对象layoutConstraints的个数由form.attributes.layoutAttributes的数量决定.

这里的LayoutConstraint是NSLayoutConstraint的子类.

• Line: 259- 274

• Description: 约束更新

• Note:

    guard let item = self.from.layoutConstraintItem else {
        print("WARNING: SnapKit failed to get from item from constraint. Activate will be a no-op.")
        return
    }
    if updatingExisting {
        var existingLayoutConstraints: [LayoutConstraint] = []
        for constraint in item.constraints {
            existingLayoutConstraints += constraint.layoutConstraints
        }
  
        for layoutConstraint in layoutConstraints {
            let existingLayoutConstraint = existingLayoutConstraints.first { $0 == layoutConstraint }
            guard let updateLayoutConstraint = existingLayoutConstraint else {
                fatalError("Updated constraint could not find existing matching constraint to update: \(layoutConstraint)")
            }
  
            let updateLayoutAttribute = (updateLayoutConstraint.secondAttribute == .notAnAttribute) ? updateLayoutConstraint.firstAttribute : updateLayoutConstraint.secondAttribute
            updateLayoutConstraint.constant = self.constant.constraintConstantTargetValueFor(layoutAttribute: updateLayoutAttribute)
        }
    }
  

从约束添加的view上找到所有的约束,一一比较attribute是否相同,如果没有相同的抛出异常.

ConstraintPriority.swift

• Path:/SnapKit/Source/ConstraintPriority.swift

• Line:30 - 77

• Note:

    public struct ConstraintPriority : ExpressibleByFloatLiteral, Equatable, Strideable {
        public typealias FloatLiteralType = Float
        
        public let value: Float
        
        public init(floatLiteral value: Float) {
            self.value = value
        }
        
        public init(_ value: Float) {
            self.value = value
        }
        
        public static var required: ConstraintPriority {
            return 1000.0
        }
        
        public static var high: ConstraintPriority {
            return 750.0
        }
        
        public static var medium: ConstraintPriority {
            #if os(OSX)
                return 501.0
            #else
                return 500.0
            #endif
            
        }
        
        public static var low: ConstraintPriority {
            return 250.0
        }
        
        public static func ==(lhs: ConstraintPriority, rhs: ConstraintPriority) -> Bool {
            return lhs.value == rhs.value
        }
    
        // MARK: Strideable
    
        public func advanced(by n: FloatLiteralType) -> ConstraintPriority {
            return ConstraintPriority(floatLiteral: value + n)
        }
    
        public func distance(to other: ConstraintPriority) -> FloatLiteralType {
            return other.value - value
        }
    }
  

• Description:ExpressibleByFloatLiteral协议和Strideable协议的使用 MARK

ConstraintInsets.swift

• Path: /SnapKit/Source/ConstraintInsets.swift

• Line: 31 - 35

• Note:

    #if os(iOS) || os(tvOS)
        public typealias ConstraintInsets = UIEdgeInsets
    #else
        public typealias ConstraintInsets = NSEdgeInsets
    #endif
  

• Description: typealias的一种使用场景,其他地方还有很多同样的试用场景就不一一列举了.

ConstraintAttributes.swift

• Path: /SnapKit/Source/ConstraintAttribu tes.swift

  • Line: 31 - 190
    * Note:

      internal struct ConstraintAttributes : OptionSet {
          
          internal init(rawValue: UInt) {
              self.rawValue = rawValue
          }
          internal init(_ rawValue: UInt) {
              self.init(rawValue: rawValue)
          }
          internal init(nilLiteral: ()) {
              self.rawValue = 0
          }
          
          internal private(set) var rawValue: UInt
          internal static var allZeros: ConstraintAttributes { return self.init(0) }
          internal static func convertFromNilLiteral() -> ConstraintAttributes { return self.init(0) }
          internal var boolValue: Bool { return self.rawValue != 0 }
          
          internal func toRaw() -> UInt { return self.rawValue }
          internal static func fromRaw(_ raw: UInt) -> ConstraintAttributes? { return self.init(raw) }
          internal static func fromMask(_ raw: UInt) -> ConstraintAttributes { return self.init(raw) }
          
          // normal
          
          internal static var none: ConstraintAttributes { return self.init(0) }
          internal static var left: ConstraintAttributes { return self.init(1) }
          internal static var top: ConstraintAttributes {  return self.init(2) }
          internal static var right: ConstraintAttributes { return self.init(4) }
          internal static var bottom: ConstraintAttributes { return self.init(8) }
          internal static var leading: ConstraintAttributes { return self.init(16) }
          internal static var trailing: ConstraintAttributes { return self.init(32) }
          internal static var width: ConstraintAttributes { return self.init(64) }
          internal static var height: ConstraintAttributes { return self.init(128) }
          internal static var centerX: ConstraintAttributes { return self.init(256) }
          internal static var centerY: ConstraintAttributes { return self.init(512) }
          internal static var lastBaseline: ConstraintAttributes { return self.init(1024) }
          
          @available(iOS 8.0, OSX 10.11, *)
          internal static var firstBaseline: ConstraintAttributes { return self.init(2048) }
          
          @available(iOS 8.0, *)
          internal static var leftMargin: ConstraintAttributes { return self.init(4096) }
          
          @available(iOS 8.0, *)
          internal static var rightMargin: ConstraintAttributes { return self.init(8192) }
          
          @available(iOS 8.0, *)
          internal static var topMargin: ConstraintAttributes { return self.init(16384) }
          
          @available(iOS 8.0, *)
          internal static var bottomMargin: ConstraintAttributes { return self.init(32768) }
          
          @available(iOS 8.0, *)
          internal static var leadingMargin: ConstraintAttributes { return self.init(65536) }
          
          @available(iOS 8.0, *)
          internal static var trailingMargin: ConstraintAttributes { return self.init(131072) }
          
          @available(iOS 8.0, *)
          internal static var centerXWithinMargins: ConstraintAttributes { return self.init(262144) }
          
          @available(iOS 8.0, *)
          internal static var centerYWithinMargins: ConstraintAttributes { return self.init(524288) }
          
          // aggregates
          
          internal static var edges: ConstraintAttributes { return self.init(15) }
          internal static var size: ConstraintAttributes { return self.init(192) }
          internal static var center: ConstraintAttributes { return self.init(768) }
          
          @available(iOS 8.0, *)
          internal static var margins: ConstraintAttributes { return self.init(61440) }
          
          @available(iOS 8.0, *)
          internal static var centerWithinMargins: ConstraintAttributes { return self.init(786432) }
          
          internal var layoutAttributes:[LayoutAttribute] {
              var attrs = [LayoutAttribute]()
              if (self.contains(ConstraintAttributes.left)) {
                  attrs.append(.left)
              }
              if (self.contains(ConstraintAttributes.top)) {
                  attrs.append(.top)
              }
              if (self.contains(ConstraintAttributes.right)) {
                  attrs.append(.right)
              }
              if (self.contains(ConstraintAttributes.bottom)) {
                  attrs.append(.bottom)
              }
              if (self.contains(ConstraintAttributes.leading)) {
                  attrs.append(.leading)
              }
              if (self.contains(ConstraintAttributes.trailing)) {
                  attrs.append(.trailing)
              }
              if (self.contains(ConstraintAttributes.width)) {
                  attrs.append(.width)
              }
              if (self.contains(ConstraintAttributes.height)) {
                  attrs.append(.height)
              }
              if (self.contains(ConstraintAttributes.centerX)) {
                  attrs.append(.centerX)
              }
              if (self.contains(ConstraintAttributes.centerY)) {
                  attrs.append(.centerY)
              }
              if (self.contains(ConstraintAttributes.lastBaseline)) {
                  attrs.append(.lastBaseline)
              }
              
              #if os(iOS) || os(tvOS)
                  if (self.contains(ConstraintAttributes.firstBaseline)) {
                      attrs.append(.firstBaseline)
                  }
                  if (self.contains(ConstraintAttributes.leftMargin)) {
                      attrs.append(.leftMargin)
                  }
                  if (self.contains(ConstraintAttributes.rightMargin)) {
                      attrs.append(.rightMargin)
                  }
                  if (self.contains(ConstraintAttributes.topMargin)) {
                      attrs.append(.topMargin)
                  }
                  if (self.contains(ConstraintAttributes.bottomMargin)) {
                      attrs.append(.bottomMargin)
                  }
                  if (self.contains(ConstraintAttributes.leadingMargin)) {
                      attrs.append(.leadingMargin)
                  }
                  if (self.contains(ConstraintAttributes.trailingMargin)) {
                      attrs.append(.trailingMargin)
                  }
                  if (self.contains(ConstraintAttributes.centerXWithinMargins)) {
                      attrs.append(.centerXWithinMargins)
                  }
                  if (self.contains(ConstraintAttributes.centerYWithinMargins)) {
                      attrs.append(.centerYWithinMargins)
                  }
              #endif
              
              return attrs
          }
      }
      
      internal func + (left: ConstraintAttributes, right: ConstraintAttributes) -> ConstraintAttributes {
          return left.union(right)
      }
      
      internal func +=(left: inout ConstraintAttributes, right: ConstraintAttributes) {
          left.formUnion(right)
      }
      
      internal func -=(left: inout ConstraintAttributes, right: ConstraintAttributes) {
          left.subtract(right)
      }
      
      internal func ==(left: ConstraintAttributes, right: ConstraintAttributes) -> Bool {
          return left.rawValue == right.rawValue
      }
    

• Description: OptionSet用法 mark

Targets

• Path: /SnapKit-develop/Source/*Targte.swfit
• Note:

    public protocol ConstraintRelatableTarget {
    }
    
    extension Int: ConstraintRelatableTarget {
    }
    
    extension UInt: ConstraintRelatableTarget {
    }
    
    extension Float: ConstraintRelatableTarget {
    }
    
    extension Double: ConstraintRelatableTarget {
    }
    
    extension CGFloat: ConstraintRelatableTarget {
    }
    
    extension CGSize: ConstraintRelatableTarget {
    }
    
    extension CGPoint: ConstraintRelatableTarget {
    }
    
    extension ConstraintInsets: ConstraintRelatableTarget {
    }
    
    extension ConstraintItem: ConstraintRelatableTarget {
    }
    
    extension ConstraintView: ConstraintRelatableTarget {
    }
    
    @available(iOS 9.0, OSX 10.11, *)
    extension ConstraintLayoutGuide: ConstraintRelatableTarget {
    }

• Description: 使用协议扩展接口支持类型.

Maker

• Note:

  class ConstraintMakerFinalizable

  class ConstraintMakerPriortizable: ConstraintMakerFinalizable

  class ConstraintMakerEditable: ConstraintMakerPriortizable

    // multipliedBy() -> ConstraintMakerEditable
    // offset() -> ConstraintMakerEditable
    // priority() -> ConstraintMakerPriortizable
    // labeled() -> ConstraintMakerFinalizable
    maker.top.equalToSuperview().multipliedBy(0.5).offset(10).priority(.required).labeled("label")

子类可以调用父类的方法,但是父类不能调用子类的方法.   

上面的链式语法通过这样的方式显示使用者调用规范.

    maker.top.equalToSuperview().offset(10).priority(.required).labeled("label").multipliedBy(05)
    // compile error