React16源码: React中的completeWork对HostText处理含更新的源码实现

HostText

1 ）概述

• 在 completeWork 中 对 HostText的处理
• 在第一次挂载和后续更新的不同条件下进行操作
  • 第一次挂载主要是创建实例
  • 后续更新其实也是重新创建实例

2 ）源码

定位到 packages/react-reconciler/src/ReactFiberCompleteWork.js#L663

到 case HostText 这里

case HostText: {
  let newText = newProps;
  // 符合这个条件，说明它不是第一次渲染，就是更新的状态
  // 调用 updateHostText 进行更新
  if (current && workInProgress.stateNode != null) {
    const oldText = current.memoizedProps;
    // If we have an alternate, that means this is an update and we need
    // to schedule a side-effect to do the updates.
    updateHostText(current, workInProgress, oldText, newText);
  } else {
    // 对于第一次渲染
    if (typeof newText !== 'string') {
      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.
    }
    // 跳过 context 处理
    const rootContainerInstance = getRootHostContainer();
    const currentHostContext = getHostContext();
    // 跳过 hydrate 处理
    let wasHydrated = popHydrationState(workInProgress);
    if (wasHydrated) {
      if (prepareToHydrateHostTextInstance(workInProgress)) {
        markUpdate(workInProgress);
      }
    } else {
      // 创建 文本 实例
      workInProgress.stateNode = createTextInstance(
        newText,
        rootContainerInstance,
        currentHostContext,
        workInProgress,
      );
    }
  }
  break;
}

• 进入 updateHostText

  updateHostText = function(
    current: Fiber,
    workInProgress: Fiber,
    oldText: string,
    newText: string,
  ) {
    // 这个非常简单，通过前后 text 是否有区别
    // 如果不同，则创建新的 text实例
    if (oldText !== newText) {
      // If the text content differs, we'll create a new text instance for it.
      // 先跳过 context 的处理
      const rootContainerInstance = getRootHostContainer();
      const currentHostContext = getHostContext();
      workInProgress.stateNode = createTextInstance(
        newText,
        rootContainerInstance,
        currentHostContext,
        workInProgress,
      );
      // We'll have to mark it as having an effect, even though we won't use the effect for anything.
      // This lets the parents know that at least one of their children has changed.
      markUpdate(workInProgress);
    }
  };
  

  • 进入 createTextInstance

    // packages/react-dom/src/client/ReactDOMHostConfig.js#L272
    export function createTextInstance(
      text: string,
      rootContainerInstance: Container,
      hostContext: HostContext,
      internalInstanceHandle: Object,
    ): TextInstance {
      if (__DEV__) {
        const hostContextDev = ((hostContext: any): HostContextDev);
        validateDOMNesting(null, text, hostContextDev.ancestorInfo);
      }
      const textNode: TextInstance = createTextNode(text, rootContainerInstance);
      // 这个方法之前阅过
      precacheFiberNode(internalInstanceHandle, textNode);
      return textNode;
    }
    

    • 进入 createTextNode

      export function createTextNode(
        text: string,
        rootContainerElement: Element | Document,
      ): Text {
        // 最终 getOwnerDocumentFromRootContainer 这里返回一个dom对象，调用dom的 createTextNode 这个方法
        return getOwnerDocumentFromRootContainer(rootContainerElement).createTextNode(
          text,
        );
      }
      

      • 进入 getOwnerDocumentFromRootContainer

      function getOwnerDocumentFromRootContainer(
        rootContainerElement: Element | Document,
      ): Document {
        // rootContainerElement.ownerDocument 这里是 window.document 对象
        // 这么做是为了兼容多平台api的使用
        return rootContainerElement.nodeType === DOCUMENT_NODE
          ? (rootContainerElement: any)
          : rootContainerElement.ownerDocument;
      }
      

• HostText 相比于 HostComponents 来说，它没有多种选择

• 没有各种各样的属性，整体来说非常的简单

• 一些特别说明的，写在了上述代码注释中