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