vue响应式原理专题

vue响应式原理专题

1、vue何时做响应式？

1.vue的构造函数调用init

备注：

1.vue的所有方法都是通过挂到prototype上的

function Vue (options) {
  if (process.env.NODE_ENV !== 'production' &&
    !(this instanceof Vue)
  ) {
    warn('Vue is a constructor and should be called with the `new` keyword')
  }
  this._init(options) // 初始化调用 找到下步
}

2.init的initState()

备注：

1. 从以下代码易知道初始化执行顺序为：
   beforeCreate -> inject的处理 -> state的处理 -> provider处理

Vue.prototype._init = function (options?: Object) {
    const vm: Component = this
    // a uid
    vm._uid = uid++


    // a flag to avoid this being observed
    vm._isVue = true
    // merge options
    if (options && options._isComponent) {
      // optimize internal component instantiation
      // since dynamic options merging is pretty slow, and none of the
      // internal component options needs special treatment.
      initInternalComponent(vm, options)
    } else {
      // 根走这一步, 合并挂载到静态的Vue.options
      vm.$options = mergeOptions(
        resolveConstructorOptions(vm.constructor),
        options || {},
        vm
      )
    }

    vm._renderProxy = vm

    // expose real self
    vm._self = vm
    initLifecycle(vm)
    initEvents(vm) // 父传进来的事件
    initRender(vm)
    callHook(vm, 'beforeCreate')
    
    // 在这类做响应式 ----
    initInjections(vm) // resolve injections before data/props
    initState(vm)
    initProvide(vm) // resolve provide after data/props
    
    callHook(vm, 'created')


    if (vm.$options.el) {
      vm.$mount(vm.$options.el)
    }
  }

3. initState做响应式

从代码易知对数据的顺序:

// state.js

export function initState (vm: Component) {
  vm._watchers = []
  const opts = vm.$options
  // 处理props
  if (opts.props) initProps(vm, opts.props)
  // 处理methods
  if (opts.methods) initMethods(vm, opts.methods)
   // 处理data
  if (opts.data) {
    initData(vm)
  } else {
    observe(vm._data = {}, true /* asRootData */)
  }
  
  if (opts.computed) initComputed(vm, opts.computed)
  
  if (opts.watch && opts.watch !== nativeWatch) {
    initWatch(vm, opts.watch)
  }
}

4、关注initData

function initData (vm: Component) {

  // 获取data
  let data = vm.$options.data
  data = vm._data = typeof data === 'function'
    ? getData(data, vm)
    : data || {}
    
  // 返回对象必须是一个普通对象， 否则dev警告提示
  if (!isPlainObject(data)) {
    data = {}
    process.env.NODE_ENV !== 'production' && warn(
      'data functions should return an object:\n' +
      'https://vuejs.org/v2/guide/components.html#data-Must-Be-a-Function',
      vm
    )
  }
  
  
  // proxy data on instance
  const keys = Object.keys(data)
  const props = vm.$options.props
  const methods = vm.$options.methods
  let i = keys.length
  
  while (i--) {
    const key = keys[i]
    // 和方法重名提示
    if (process.env.NODE_ENV !== 'production') {
      if (methods && hasOwn(methods, key)) {
        warn(
          `Method "${key}" has already been defined as a data property.`,
          vm
        )
      }
    }
    // 和props属性重名提示
    if (props && hasOwn(props, key)) {
      process.env.NODE_ENV !== 'production' && warn(
        `The data property "${key}" is already declared as a prop. ` +
        `Use prop default value instead.`,
        vm
      )
    // 特殊键值直接返回初始对象的值
    } else if (!isReserved(key)) {
      proxy(vm, `_data`, key)
    }
  }
  
  // 开始做响应式
  // observe data
  observe(data, true /* asRootData */)
}

---

2、怎样做响应式的？

1.调用流程顺序：
调用observe方法 --->通过new Observer(ob)生成观察对象 --->Observer内部constructor时做响应式 ---> （若是对象）调用walk(value)具体实现

observe方法解析

export function observe (value: any, asRootData: ?boolean): Observer | void {
  // 只能对对象进行处理
  if (!isObject(value) || value instanceof VNode) {
    return
  }
  // ob
  let ob: Observer | void
  
  // 通过判断是否有__ob__对象来判断是否做了响应式
  if (hasOwn(value, '__ob__') && value.__ob__ instanceof Observer) {
    ob = value.__ob__
  } else if (
    shouldObserve && //默认为true
    !isServerRendering() && // 非服务器渲染
    (Array.isArray(value) || isPlainObject(value)) &&
    Object.isExtensible(value) &&
    !value._isVue
  ) {
    ob = new Observer(value) // 这里做响应式
  }
  if (asRootData && ob) {
    ob.vmCount++
  }
  return ob
}

Observer对象解析

1、图解

2、代码解析

export class Observer {
  value: any;
  dep: Dep;
  vmCount: number; // number of vms that have this object as root $data

  constructor (value: any) {
    this.value = value
    this.dep = new Dep()
    this.vmCount = 0
    
    def(value, '__ob__', this) // 给this挂上__ob__
    
    if (Array.isArray(value)) {
      if (hasProto) {
        protoAugment(value, arrayMethods)
      } else {
        copyAugment(value, arrayMethods, arrayKeys)
      }
      this.observeArray(value)
    } else {
      this.walk(value)
    }
  }

  /**
   * Walk through all properties and convert them into
   * getter/setters. This method should only be called when
   * value type is Object.
   */
  walk (obj: Object) {
    const keys = Object.keys(obj)
    for (let i = 0; i < keys.length; i++) {
      defineReactive(obj, keys[i])
    }
  }
  
  // .... 其他方法
}

通过walk 我们知道defineReactive()方法， 接下来对defineReactive解析

3、defineReactive 针对对象作dep收集watcher

源码位置：src\core\observer\index.js

参考

export function defineReactive (
  obj: Object,
  key: string,
  val: any,
  customSetter?: ?Function,
  shallow?: boolean
) {
  const dep = new Dep()

  const property = Object.getOwnPropertyDescriptor(obj, key)
  if (property && property.configurable === false) {
    return
  }

  // cater for pre-defined getter/setters
  const getter = property && property.get
  const setter = property && property.set
  // val赋初值
  if ((!getter || setter) && arguments.length === 2) {
    val = obj[key]
  }

  let childOb = !shallow && observe(val)
  Object.defineProperty(obj, key, {
    enumerable: true,
    configurable: true,
    get: function reactiveGetter () {
      const value = getter ? getter.call(obj) : val
      if (Dep.target) {
        dep.depend()
        if (childOb) {
          childOb.dep.depend()
          if (Array.isArray(value)) {
            dependArray(value)
          }
        }
      }
      return value
    },
    set: function reactiveSetter (newVal) {
      const value = getter ? getter.call(obj) : val
      /* eslint-disable no-self-compare */
      if (newVal === value || (newVal !== newVal && value !== value)) {
        return
      }
      /* eslint-enable no-self-compare */
      if (process.env.NODE_ENV !== 'production' && customSetter) {
        customSetter()
      }
      // #7981: for accessor properties without setter
      if (getter && !setter) return
      if (setter) {
        setter.call(obj, newVal)
      } else {
        val = newVal
      }
      childOb = !shallow && observe(newVal)
      dep.notify()
    }
  })
}

以上代码的意思是

get操作进行是 如果Dep.target存在，即有watcher处在正在收集的状况，dep.depend()触发后当前watcher进行addDep(this)

watcher.addDep(dep) ---> watcher.newDeps.push(dep) 即watcher保存dep

同时 dep.addSub(this)

watcher 和 dep相互保存。

这样dep可以通过notify触发。

4、针对数组做响应式

对数组的每一个对象作响应式，不是对象则不是响应式

  observeArray (items: Array<any>) {
    for (let i = 0, l = items.length; i < l; i++) {
      observe(items[i])
    }
  }