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;
}