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

最后编辑于：2018.01.06 18:14:01

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SnapKit 源码阅读笔记

Basic Information

Note

Constraint.swift

ConstraintPriority.swift

ConstraintInsets.swift

ConstraintAttributes.swift

Targets

Maker

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