completeWork

1 ）概述

• 在 completeUnitOfWork 当中，在节点是正常渲染没有任何出错的情况下
• 会去调用 completework，对这个节点进行一个完成工作的一系列操作
• 在update各种component的时候，执行了各种获取context相关的内容
• 对于 completeWork，我们会把它对应的这些节点获取的context再pop出来
• 相当于 beginWork是一个正向的流程, 而completeWork 是一个反向的流程
• 正向的流程获取的内容，反向的流程给它依次pop出来
• 最终能够达到一个再被清空的一个流程
• 对于 HostComponent 会执行一个节点的初始化以及更新的一个操作
• 然后会初始化监听事件

2 ）源码

定位到 packages/react-reconciler/src/ReactFiberCompleteWork.js#L540

进入 completeWork

function completeWork(
  current: Fiber | null,
  workInProgress: Fiber,
  renderExpirationTime: ExpirationTime,
): Fiber | null {
  // 获取当前 props
  const newProps = workInProgress.pendingProps;

  // 这里和 beginWork 里面的代码很像
  // 在这里面，很多的组件是没有任何的一个工作要做的
  // 相对于 class component，它也只需要去pop之前可能push进去过的一些内容
  switch (workInProgress.tag) {
    case IndeterminateComponent:
      break;
    case LazyComponent:
      break;
    case SimpleMemoComponent:
    case FunctionComponent:
      break;
    case ClassComponent: {
      const Component = workInProgress.type;
      if (isLegacyContextProvider(Component)) {
        popLegacyContext(workInProgress);
      }
      break;
    }
    // 对于 HostRoot，它也是各种 pop，因为 HostRoot 它会获取很多的一些内容
    case HostRoot: {
      popHostContainer(workInProgress);
      popTopLevelLegacyContextObject(workInProgress);
      const fiberRoot = (workInProgress.stateNode: FiberRoot);
      if (fiberRoot.pendingContext) {
        fiberRoot.context = fiberRoot.pendingContext;
        fiberRoot.pendingContext = null;
      }
      if (current === null || current.child === null) {
        // If we hydrated, pop so that we can delete any remaining children
        // that weren't hydrated.
        popHydrationState(workInProgress);
        // This resets the hacky state to fix isMounted before committing.
        // TODO: Delete this when we delete isMounted and findDOMNode.
        workInProgress.effectTag &= ~Placement;
      }
      // 最终它这边执行了一个叫做 updateHostContainer 这个方法
      // 那么这个方法在 react-dom 的环境下面是一个空的方法
      updateHostContainer(workInProgress);
      break;
    }
    // 最复杂的是 HostComponent 处理
    case HostComponent: {
      popHostContext(workInProgress);
      const rootContainerInstance = getRootHostContainer();
      const type = workInProgress.type;
      if (current !== null && workInProgress.stateNode != null) {
        updateHostComponent(
          current,
          workInProgress,
          type,
          newProps,
          rootContainerInstance,
        );

        if (current.ref !== workInProgress.ref) {
          markRef(workInProgress);
        }
      } else {
        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;
        }

        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 {
          let instance = createInstance(
            type,
            newProps,
            rootContainerInstance,
            currentHostContext,
            workInProgress,
          );

          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 (
            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;
    }
    // HostText 的处理
    case HostText: {
      let newText = newProps;
      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 {
        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.
        }
        const rootContainerInstance = getRootHostContainer();
        const currentHostContext = getHostContext();
        let wasHydrated = popHydrationState(workInProgress);
        if (wasHydrated) {
          if (prepareToHydrateHostTextInstance(workInProgress)) {
            markUpdate(workInProgress);
          }
        } else {
          workInProgress.stateNode = createTextInstance(
            newText,
            rootContainerInstance,
            currentHostContext,
            workInProgress,
          );
        }
      }
      break;
    }
    case ForwardRef:
      break;
    // SuspenseComponent 的处理
    case SuspenseComponent: {
      const nextState = workInProgress.memoizedState;
      if ((workInProgress.effectTag & DidCapture) !== NoEffect) {
        // Something suspended. Re-render with the fallback children.
        workInProgress.expirationTime = renderExpirationTime;
        // Do not reset the effect list.
        return workInProgress;
      }

      const nextDidTimeout = nextState !== null;
      const prevDidTimeout = current !== null && current.memoizedState !== null;

      if (current !== null && !nextDidTimeout && prevDidTimeout) {
        // We just switched from the fallback to the normal children. Delete
        // the fallback.
        // TODO: Would it be better to store the fallback fragment on
        // the stateNode during the begin phase?
        const currentFallbackChild: Fiber | null = (current.child: any).sibling;
        if (currentFallbackChild !== null) {
          // Deletions go at the beginning of the return fiber's effect list
          const first = workInProgress.firstEffect;
          if (first !== null) {
            workInProgress.firstEffect = currentFallbackChild;
            currentFallbackChild.nextEffect = first;
          } else {
            workInProgress.firstEffect = workInProgress.lastEffect = currentFallbackChild;
            currentFallbackChild.nextEffect = null;
          }
          currentFallbackChild.effectTag = Deletion;
        }
      }

      // The children either timed out after previously being visible, or
      // were restored after previously being hidden. Schedule an effect
      // to update their visiblity.
      if (
        //
        nextDidTimeout !== prevDidTimeout ||
        // Outside concurrent mode, the primary children commit in an
        // inconsistent state, even if they are hidden. So if they are hidden,
        // we need to schedule an effect to re-hide them, just in case.
        ((workInProgress.effectTag & ConcurrentMode) === NoContext &&
          nextDidTimeout)
      ) {
        workInProgress.effectTag |= Update;
      }
      break;
    }
    case Fragment:
      break;
    case Mode:
      break;
    case Profiler:
      break;
    // 后续可以看到每一个基本上都是pop出来一些container，还有context相关的东西
    case HostPortal:
      popHostContainer(workInProgress);
      updateHostContainer(workInProgress);
      break;
    case ContextProvider:
      // Pop provider fiber
      popProvider(workInProgress);
      break;
    case ContextConsumer:
      break;
    case MemoComponent:
      break;
    case IncompleteClassComponent: {
      // Same as class component case. I put it down here so that the tags are
      // sequential to ensure this switch is compiled to a jump table.
      const Component = workInProgress.type;
      if (isLegacyContextProvider(Component)) {
        popLegacyContext(workInProgress);
      }
      break;
    }
    default:
      invariant(
        false,
        'Unknown unit of work tag. This error is likely caused by a bug in ' +
          'React. Please file an issue.',
      );
  }

  return null;
}

• 关于 updateHostContainer, 不仅是这个方法，下面的方法
  • appendAllChildren
  • updateHostComponent
  • updateHostText
• 以上4个，会根据环境的不同来执行不同的操作
• 在 ReactDOMHostConfig.js 中 supportsMutation 为true
  • 这时候 updateHostContainer 就是一个空的方法
• 这里主要关注，HostComponent 以及 HostText，在 completeWork 中的操作
• 在这里，目前只看大致的流程，后续会对细节做具体的分析