React16源码: React中的completeWork对HostComponent处理的源码实现

HostComponent

1 ）概述

• 在 completeWork 当中，我们需要对 HostComponent 的一些操作有哪些?
  • 首先在一次更新而不是初次渲染的情况下
  • 需要去 diffProperties 来计算，需要更新的内容
  • 也就是在 vdom 中去进行一个对比来判断这一个节点是否需要真的去更新它
  • 以此来最低程度的去更新整个 dom 的一个过程
  • 对于不同 dom property，它有一些不同的处理方式

2 ）源码

定位到 packages/react-reconciler/src/ReactFiberCompleteWork.js#L581

找到 case HostComponent

case HostComponent: {
  // 跳过
  popHostContext(workInProgress);
  // 跳过
  const rootContainerInstance = getRootHostContainer();
  const type = workInProgress.type;
  // 不是第一次渲染，也就是更新的时候
  if (current !== null && workInProgress.stateNode != null) {
    updateHostComponent(
      current,
      workInProgress,
      type,
      newProps,
      rootContainerInstance,
    );

    if (current.ref !== workInProgress.ref) {
      markRef(workInProgress); // 跳过
    }
  } else {
    // 第一次挂载渲染
    // 没有 props 说明有问题，提示
    if (!newProps) {
      invariant(
        workInProgress.stateNode !== null,
        'We must have new props for new mounts. This error is likely ' +
          'caused by a bug in React. Please file an issue.',
      );
      // This can happen when we abort work.
      break;
    }
    // 跳过
    const currentHostContext = getHostContext();
    // TODO: Move createInstance to beginWork and keep it on a context
    // "stack" as the parent. Then append children as we go in beginWork
    // or completeWork depending on we want to add then top->down or
    // bottom->up. Top->down is faster in IE11.
    let wasHydrated = popHydrationState(workInProgress);
    if (wasHydrated) {
      // TODO: Move this and createInstance step into the beginPhase
      // to consolidate.
      if (
        prepareToHydrateHostInstance(
          workInProgress,
          rootContainerInstance,
          currentHostContext,
        )
      ) {
        // If changes to the hydrated node needs to be applied at the
        // commit-phase we mark this as such.
        markUpdate(workInProgress);
      }
    } else {
      // 第一次挂载
      // 注意，这里，创建 element的过程
      let instance = createInstance(
        type,
        newProps,
        rootContainerInstance,
        currentHostContext,
        workInProgress,
      );

      // 第一次渲染，要添加子节点
      appendAllChildren(instance, workInProgress, false, false);

      // Certain renderers require commit-time effects for initial mount.
      // (eg DOM renderer supports auto-focus for certain elements).
      // Make sure such renderers get scheduled for later work.
      if (
        // 主要功能: 对dom节点上面的可能的事件监听，需要初始化整个react的事件体系
        finalizeInitialChildren(
          instance,
          type,
          newProps,
          rootContainerInstance,
          currentHostContext,
        )
      ) {
        markUpdate(workInProgress);
      }
      workInProgress.stateNode = instance;
    }

    if (workInProgress.ref !== null) {
      // If there is a ref on a host node we need to schedule a callback
      markRef(workInProgress);
    }
  }
  break;
}

• 进入 createInstance

  // packages/react-dom/src/client/ReactDOMHostConfig.js#L167
  // 这个方法就是创建节点的过程
  export function createInstance(
    type: string,
    props: Props,
    rootContainerInstance: Container,
    hostContext: HostContext,
    internalInstanceHandle: Object,
  ): Instance {
    let parentNamespace: string;
    if (__DEV__) {
      // TODO: take namespace into account when validating.
      const hostContextDev = ((hostContext: any): HostContextDev);
      validateDOMNesting(type, null, hostContextDev.ancestorInfo);
      if (
        typeof props.children === 'string' ||
        typeof props.children === 'number'
      ) {
        const string = '' + props.children;
        const ownAncestorInfo = updatedAncestorInfo(
          hostContextDev.ancestorInfo,
          type,
        );
        validateDOMNesting(null, string, ownAncestorInfo);
      }
      parentNamespace = hostContextDev.namespace;
    } else {
      parentNamespace = ((hostContext: any): HostContextProd);
    }
    // 主要在这里
    const domElement: Instance = createElement(
      type,
      props,
      rootContainerInstance,
      parentNamespace,
    );
    // 后面会进入这个方法
    precacheFiberNode(internalInstanceHandle, domElement);
    // 同上
    updateFiberProps(domElement, props);
    return domElement;
  }
  

• 进入 createElement

  // 不展开这个方法里面调用的内容
  export function createElement(
    type: string,
    props: Object,
    rootContainerElement: Element | Document,
    parentNamespace: string,
  ): Element {
    let isCustomComponentTag;
  
    // We create tags in the namespace of their parent container, except HTML
    // tags get no namespace.
    // 先要获取 document, 先要通过 document 的api来创建
    const ownerDocument: Document = getOwnerDocumentFromRootContainer(
      rootContainerElement,
    );
    let domElement: Element;
    let namespaceURI = parentNamespace;
    // 在React中有区分，不同节点类型，都会有一个定义，比如html普通节点, svg节点等
    if (namespaceURI === HTML_NAMESPACE) {
      namespaceURI = getIntrinsicNamespace(type);
    }
    // 如果是 html 类型节点，做一些特殊处理
    if (namespaceURI === HTML_NAMESPACE) {
      if (__DEV__) {
        isCustomComponentTag = isCustomComponent(type, props);
        // Should this check be gated by parent namespace? Not sure we want to
        // allow <SVG> or <mATH>.
        warning(
          isCustomComponentTag || type === type.toLowerCase(),
          '<%s /> is using incorrect casing. ' +
            'Use PascalCase for React components, ' +
            'or lowercase for HTML elements.',
          type,
        );
      }
      // 对script节点进行特殊处理
      if (type === 'script') {
        // Create the script via .innerHTML so its "parser-inserted" flag is
        // set to true and it does not execute
        const div = ownerDocument.createElement('div');
        div.innerHTML = '<script><' + '/script>'; // eslint-disable-line
        // This is guaranteed to yield a script element.
        const firstChild = ((div.firstChild: any): HTMLScriptElement);
        domElement = div.removeChild(firstChild);
      } else if (typeof props.is === 'string') {
        // $FlowIssue `createElement` should be updated for Web Components
        domElement = ownerDocument.createElement(type, {is: props.is});
      } else {
        // Separate else branch instead of using `props.is || undefined` above because of a Firefox bug.
        // See discussion in https://github.com/facebook/react/pull/6896
        // and discussion in https://bugzilla.mozilla.org/show_bug.cgi?id=1276240
        domElement = ownerDocument.createElement(type);
        // Normally attributes are assigned in `setInitialDOMProperties`, however the `multiple`
        // attribute on `select`s needs to be added before `option`s are inserted. This prevents
        // a bug where the `select` does not scroll to the correct option because singular
        // `select` elements automatically pick the first item.
        // See https://github.com/facebook/react/issues/13222
        if (type === 'select' && props.multiple) {
          const node = ((domElement: any): HTMLSelectElement);
          node.multiple = true;
        }
      }
    } else {
      domElement = ownerDocument.createElementNS(namespaceURI, type);
    }
  
    if (__DEV__) {
      if (namespaceURI === HTML_NAMESPACE) {
        if (
          !isCustomComponentTag &&
          Object.prototype.toString.call(domElement) ===
            '[object HTMLUnknownElement]' &&
          !Object.prototype.hasOwnProperty.call(warnedUnknownTags, type)
        ) {
          warnedUnknownTags[type] = true;
          warning(
            false,
            'The tag <%s> is unrecognized in this browser. ' +
              'If you meant to render a React component, start its name with ' +
              'an uppercase letter.',
            type,
          );
        }
      }
    }
  
    return domElement;
  }
  

• 进入 precacheFiberNode

  const internalInstanceKey = '__reactInternalInstance$' + randomKey;
  
  // 就是在node上挂载上述属性
  // hostInst, node 对应着 internalInstanceHandle, domElement
  // 相当于在 对应dom节点上，通过 internalInstanceKey 这个 key
  // 去创建一个指向 fiber 对象的引用
  // 后期，我们想要从dom对象上获取对应的 fiber就可以方便获取
  export function precacheFiberNode(hostInst, node) {
    node[internalInstanceKey] = hostInst;
  }
  

• 进入 updateFiberProps

  const internalEventHandlersKey = '__reactEventHandlers$' + randomKey;
  
  // 两个参数 node 和 props, 对应着 domElement, props
  // 在 domElement 上用一个key 存储 props
  // props 会对应到上面 domElement 的 attribute, 所以，有对应关系，方便后期取用
  export function updateFiberProps(node, props) {
    node[internalEventHandlersKey] = props;
  }
  

• 进入 appendAllChildren

  appendAllChildren = function(
    parent: Instance,
    workInProgress: Fiber,
    needsVisibilityToggle: boolean,
    isHidden: boolean,
  ) {
    // We only have the top Fiber that was created but we need recurse down its
    // children to find all the terminal nodes.
    let node = workInProgress.child;
    // 这个循环的意义：对当前节点下寻找第一层的dom节点或text节点，不会append 嵌套(继续下一层)的dom节点
    // 这样做的原因，因为对每个dom节点都会有这样一个执行 completeWork 的阶段
    // 也就是当前层只找自己下一层的dom或text, 一层一层的向下找，不会存在忽略的问题
    while (node !== null) {
      if (node.tag === HostComponent || node.tag === HostText) {
        // 注意这里，挂载节点 
        // parent 是刚刚创建的 instance
        // node.stateNode 是当前节点子节点对应的Fiber对象
        // 如果说，它的子节点那一层上面发现了原生dom节点或者文本节点，就把它挂载到节点上面
        appendInitialChild(parent, node.stateNode);
      } else if (node.tag === HostPortal) {
        // If we have a portal child, then we don't want to traverse
        // down its children. Instead, we'll get insertions from each child in
        // the portal directly.
      } else if (node.child !== null) {
        // 向下遍历
        node.child.return = node;
        node = node.child;
        continue;
      }
      // 这里直接 return
      if (node === workInProgress) {
        return;
      }
      // 没有兄弟节点，向上遍历
      while (node.sibling === null) {
        if (node.return === null || node.return === workInProgress) {
          return;
        }
        node = node.return;
      }
      // 这个本来如此，对sibling进行挂载操作
      node.sibling.return = node.return;
      // 循环找 sibling 节点
      node = node.sibling;
    }
  };
  

• 进入 appendInitialChild

  // 这个函数执行的就是 dom 节点的 appendChild方法
  export function appendInitialChild(
    parentInstance: Instance,
    child: Instance | TextInstance,
  ): void {
    parentInstance.appendChild(child);
  }
  

• 以上，相关注释都在代码内，不再单独拿出详解
• 里面没涉及到的一些代码，都比较简单，不再赘述
• 主要关注上面 appendAllChildren 的算法, 内部有注释