关于前端:React-Hooks在SDWAN项目中实践

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前言

React Hooks 是 React16 新出的基于函数式组件的一组新的 api，其不同于之前 class 组件的内层嵌套形式，利用 hooks 进行钩子形式的对数据进行了组件间的流向组织，sdwan 我的项目中都是基于函数式组件的封装，本文为 sdwan 我的项目中的 react hooks 的利用实际

目录

  • 增加正告规定弹窗组件实际
  • React Hooks 源码解读
  • React Fiber 数据结构剖析

摸索案例

增加正告规定弹窗组件实际

[组件目录]

  • components

    • addRule.jsx
    • RuleList.jsx
  • index.jsx
  • index.less

[目录形容] addRule 是点击弹窗后弹出的主体组件

[源码剖析] addRule 是增加规定的弹窗，其中在告警规定一栏中，须要对列表中的行进行加减操作，这里最先想到的就是利用 useState 进行数据的治理，但其实 useState 是 useReducer 的语法糖，后续源码中会剖析，咱们看到应用了 useState 后能够将所有状态抽离到顶部，后续但凡须要应用 trNum 或 setTrNum 的便能够间接应用，这样就省去了在 setState 中的设置以及对相应 this 的绑定问题，使得数据的操作更加纯正而且清晰

const AddRule = (props) => {const { children, title} = props;
  ......

  const [trNum, setTrNum] = useState(1);

  const trLoop = (n) => {let arr = [];
    for(let i=0; i< n; i++) {
      arr.push(
        <tr>
          <td>
            <Select
              placeholder='请抉择'
              defaultValue='0'
              style={{width:'120px'}}
            >
                {options.params.map((d) => (<Select.Option value={d.status} key={d.status}>
                    {d.text}
                    </Select.Option>
                ))}
            </Select>
          </td>
          <td>
            <Select
              placeholder='请抉择'
              defaultValue='0'
            >
                {options.compare.map((d) => (<Select.Option value={d.status} key={d.status}>
                    {d.text}
                    </Select.Option>
                ))}
            </Select>
          </td>
          <td>
            <Select
              placeholder='请抉择'
              defaultValue={currentType}
              onChange={val => setTypeValue(val)}
            >
                {options.type.map((d) => (<Select.Option value={d.status} key={d.status}>
                    {d.text}
                    </Select.Option>
                ))}
            </Select>
          </td>
          <td>
            {typeValue == options.type[1].status 
            ? 
              <span style={{display: 'inline-flex', verticalAlign: 'middle', lineHeight: '32px', width: '120px'}}>
                <Input placeholder=""/>dBm
              </span>
            : 
              <Select
                placeholder='请抉择'
                defaultValue='0'
                style={{width:'120px'}}
              >
                  {options.params.map((d) => (<Select.Option value={d.status} key={d.status}>
                      {d.text}
                      </Select.Option>
                  ))}
              </Select>
            }
          </td>
          <td>
            <PlusOutlined style={{color: '#1890ff'}} onClick={()=>setTrNum(trNum + 1)}/>
          </td>
          <td>
            <CloseOutlined style={{color: '#ff4d4f'}} onClick={()=> trNum>1 && setTrNum(trNum - 1)}/>
          </td>
        </tr>
      )
    };
    return arr;
  };

  ......

  return (
    <>
      <span onClick={showModelHandler}>{children}</span>
      <Modal
        title={title}
        visible={visible}
        onCancel={hideModelHandler}
        onOk={handleOk}
        maskClosable={false}
        destroyOnClose
      >
        <Form form={form} layout="vertical">
          ......
          <Form.Item name="告警规定" label="告警规定">
              <div style={{width: '100%', backgroundColor: '#ececec', padding: '10px'}}>
                <span>
                  合乎以下 &nbsp;<Select
                    placeholder='请抉择'
                    defaultValue='0'
                    style={{width: '120px'}}
                  >
                      {options.rule.map((d) => (<Select.Option value={d.status} key={d.status}>
                          {d.text}
                          </Select.Option>
                      ))}
                  </Select>&nbsp; 条件：</span>
                <div 
                  style={{
                    border: '1px solid #ccc',
                    width: '100%', 
                    background: '#fff', 
                    marginTop: '10px', 
                    padding: '4px'
                  }}
                >
                  <table >
                    <tbody >
                      {trLoop(trNum) }
                    </tbody>
                  </table>
                </div>
              </div>
          </Form.Item>
          ......
        </Form>
      </Modal>
    </>
  );
};

React Hooks 源码解读

[组件目录]

  • packages

    • react

      • src

        • ReactHooks.js

这里仅仅是做了一个名称的导出包含：

  • useContext
  • useState
  • useReducer
  • useRef
  • useEffect
  • useLayoutEffect
  • useCallback
  • useMemo
  • useImperativeHandles
  • useDebugValue
  • useTransition
  • useDeferredValue
  • useOpaqueIdentifier
  • useMutableSource

这里真正的源码是放在了 packages/react-reconciler/src/ReactFiberHooks.js 里，能够看出其利用的依然是 React 的外围数据结构 Fiber 的调度作用

export function renderWithHooks<Props, SecondArg>(
  current: Fiber | null,
  workInProgress: Fiber,
  Component: (p: Props, arg: SecondArg) => any,
  props: Props,
  secondArg: SecondArg,
  nextRenderLanes: Lanes,
): any {
  renderLanes = nextRenderLanes;
  currentlyRenderingFiber = workInProgress;

  if (__DEV__) {
    hookTypesDev =
      current !== null
        ? ((current._debugHookTypes: any): Array<HookType>)
        : null;
    hookTypesUpdateIndexDev = -1;
    // Used for hot reloading:
    ignorePreviousDependencies =
      current !== null && current.type !== workInProgress.type;
  }

  workInProgress.memoizedState = null;
  workInProgress.updateQueue = null;
  workInProgress.lanes = NoLanes;

  // The following should have already been reset
  // currentHook = null;
  // workInProgressHook = null;

  // didScheduleRenderPhaseUpdate = false;

  // TODO Warn if no hooks are used at all during mount, then some are used during update.
  // Currently we will identify the update render as a mount because memoizedState === null.
  // This is tricky because it's valid for certain types of components (e.g. React.lazy)

  // Using memoizedState to differentiate between mount/update only works if at least one stateful hook is used.
  // Non-stateful hooks (e.g. context) don't get added to memoizedState,
  // so memoizedState would be null during updates and mounts.
  if (__DEV__) {if (current !== null && current.memoizedState !== null) {ReactCurrentDispatcher.current = HooksDispatcherOnUpdateInDEV;} else if (hookTypesDev !== null) {
      // This dispatcher handles an edge case where a component is updating,
      // but no stateful hooks have been used.
      // We want to match the production code behavior (which will use HooksDispatcherOnMount),
      // but with the extra DEV validation to ensure hooks ordering hasn't changed.
      // This dispatcher does that.
      ReactCurrentDispatcher.current = HooksDispatcherOnMountWithHookTypesInDEV;
    } else {ReactCurrentDispatcher.current = HooksDispatcherOnMountInDEV;}
  } else {
    ReactCurrentDispatcher.current =
      current === null || current.memoizedState === null
        ? HooksDispatcherOnMount
        : HooksDispatcherOnUpdate;
  }

  let children = Component(props, secondArg);

  // Check if there was a render phase update
  if (didScheduleRenderPhaseUpdateDuringThisPass) {
    // Keep rendering in a loop for as long as render phase updates continue to
    // be scheduled. Use a counter to prevent infinite loops.
    let numberOfReRenders: number = 0;
    do {
      didScheduleRenderPhaseUpdateDuringThisPass = false;
      invariant(
        numberOfReRenders < RE_RENDER_LIMIT,
        'Too many re-renders. React limits the number of renders to prevent' +
          'an infinite loop.',
      );

      numberOfReRenders += 1;
      if (__DEV__) {
        // Even when hot reloading, allow dependencies to stabilize
        // after first render to prevent infinite render phase updates.
        ignorePreviousDependencies = false;
      }

      // Start over from the beginning of the list
      currentHook = null;
      workInProgressHook = null;

      workInProgress.updateQueue = null;

      if (__DEV__) {
        // Also validate hook order for cascading updates.
        hookTypesUpdateIndexDev = -1;
      }

      ReactCurrentDispatcher.current = __DEV__
        ? HooksDispatcherOnRerenderInDEV
        : HooksDispatcherOnRerender;

      children = Component(props, secondArg);
    } while (didScheduleRenderPhaseUpdateDuringThisPass);
  }

  // We can assume the previous dispatcher is always this one, since we set it
  // at the beginning of the render phase and there's no re-entrancy.
  ReactCurrentDispatcher.current = ContextOnlyDispatcher;

  if (__DEV__) {workInProgress._debugHookTypes = hookTypesDev;}

  // This check uses currentHook so that it works the same in DEV and prod bundles.
  // hookTypesDev could catch more cases (e.g. context) but only in DEV bundles.
  const didRenderTooFewHooks =
    currentHook !== null && currentHook.next !== null;

  renderLanes = NoLanes;
  currentlyRenderingFiber = (null: any);

  currentHook = null;
  workInProgressHook = null;

  if (__DEV__) {
    currentHookNameInDev = null;
    hookTypesDev = null;
    hookTypesUpdateIndexDev = -1;
  }

  didScheduleRenderPhaseUpdate = false;

  invariant(
    !didRenderTooFewHooks,
    'Rendered fewer hooks than expected. This may be caused by an accidental' +
      'early return statement.',
  );

  return children;
}

从中抽离出外围的 hooks 渲染，其余的具体的 use 办法能够在其上进行扩大，能够看出其实质是是基于 Fiber 的 workInProgress 的全局变量的更改与调度，其中蕴含记录以后 hook 状态的 memoizedState 以及须要更新的队列 updateQueue，hooks 的队列通过 memoizedState 及 next 形成了一个链表，整个 hook 的外围是基于 Dispatcher 的切换 hook 的调用，这里就波及到 Fiber 的整个数据结构，在下一节中进行形容

React Fiber 数据结构剖析

[组件目录]

  • packages

    • react-reconciler

      • src

        • ReactFiber.js

简略来说 React 的 Fiber 数据结构是保护了一个如下的数据格式：

Fiber = {
    // 标识 fiber 类型的标签，详情参看下述 WorkTag
    tag: WorkTag,

    // 指向父节点
    return: Fiber | null,

    // 指向子节点
    child: Fiber | null,

    // 指向兄弟节点
    sibling: Fiber | null,

    // 在开始执行时设置 props 值
    pendingProps: any,

    // 在完结时设置的 props 值
    memoizedProps: any,

    // 以后 state
    memoizedState: any,

    // Effect 类型，详情查看以下 effectTag
    effectTag: SideEffectTag,

    // effect 节点指针，指向下一个 effect
    nextEffect: Fiber | null,

    // effect list 是单向链表，第一个 effect
    firstEffect: Fiber | null,

    // effect list 是单向链表，最初一个 effect
    lastEffect: Fiber | null,

    // work 的过期工夫，可用于标识一个 work 优先级程序
    expirationTime: ExpirationTime,
};

该数据结构是一个通过链表实现的树的构造，整个 React 的阶段可分为 Render Phase、Pre-Commit Phase 以及 Commit Phase，Fiber 的设计初衷是利用浏览器渲染过程中残余的工夫碎片来进行 render，而要达到这个目标须要可能对渲染过程的工作进行暂停、终止以及复用，Fiber 便是利用数据结构实现了这样一个虚构堆栈帧。

这里不再对协调 (Reconciliation) 和调度 (Scheduling) 的具体过程，如 expirationTime 的权重设计、Effect lists 的 DFS 算法设计等进行讲述，有趣味的同学能够参看这篇文章(React Fiber 源码解析)

基于 React Hooks 波及到的 workInProgress，咱们重点看一下这里的设计

// This is used to create an alternate fiber to do work on.
export function createWorkInProgress(current: Fiber, pendingProps: any): Fiber {
  let workInProgress = current.alternate;
  if (workInProgress === null) {
    // We use a double buffering pooling technique because we know that we'll
    // only ever need at most two versions of a tree. We pool the "other" unused
    // node that we're free to reuse. This is lazily created to avoid allocating
    // extra objects for things that are never updated. It also allow us to
    // reclaim the extra memory if needed.
    workInProgress = createFiber(
      current.tag,
      pendingProps,
      current.key,
      current.mode,
    );
    workInProgress.elementType = current.elementType;
    workInProgress.type = current.type;
    workInProgress.stateNode = current.stateNode;

    if (__DEV__) {
      // DEV-only fields
      workInProgress._debugID = current._debugID;
      workInProgress._debugSource = current._debugSource;
      workInProgress._debugOwner = current._debugOwner;
      workInProgress._debugHookTypes = current._debugHookTypes;
    }

    workInProgress.alternate = current;
    current.alternate = workInProgress;
  } else {
    workInProgress.pendingProps = pendingProps;
    // Needed because Blocks store data on type.
    workInProgress.type = current.type;

    // We already have an alternate.
    workInProgress.subtreeTag = NoSubtreeEffect;
    workInProgress.deletions = null;

    // The effect list is no longer valid.
    workInProgress.nextEffect = null;
    workInProgress.firstEffect = null;
    workInProgress.lastEffect = null;

    if (enableProfilerTimer) {
      // We intentionally reset, rather than copy, actualDuration & actualStartTime.
      // This prevents time from endlessly accumulating in new commits.
      // This has the downside of resetting values for different priority renders,
      // But works for yielding (the common case) and should support resuming.
      workInProgress.actualDuration = 0;
      workInProgress.actualStartTime = -1;
    }
  }

  // Reset all effects except static ones.
  // Static effects are not specific to a render.
  workInProgress.effectTag = current.effectTag & StaticMask;
  workInProgress.childLanes = current.childLanes;
  workInProgress.lanes = current.lanes;

  workInProgress.child = current.child;
  workInProgress.memoizedProps = current.memoizedProps;
  workInProgress.memoizedState = current.memoizedState;
  workInProgress.updateQueue = current.updateQueue;

  // Clone the dependencies object. This is mutated during the render phase, so
  // it cannot be shared with the current fiber.
  const currentDependencies = current.dependencies;
  workInProgress.dependencies =
    currentDependencies === null
      ? null
      : {
          lanes: currentDependencies.lanes,
          firstContext: currentDependencies.firstContext,
        };

  // These will be overridden during the parent's reconciliation
  workInProgress.sibling = current.sibling;
  workInProgress.index = current.index;
  workInProgress.ref = current.ref;

  if (enableProfilerTimer) {
    workInProgress.selfBaseDuration = current.selfBaseDuration;
    workInProgress.treeBaseDuration = current.treeBaseDuration;
  }

  if (__DEV__) {
    workInProgress._debugNeedsRemount = current._debugNeedsRemount;
    switch (workInProgress.tag) {
      case IndeterminateComponent:
      case FunctionComponent:
      case SimpleMemoComponent:
        workInProgress.type = resolveFunctionForHotReloading(current.type);
        break;
      case ClassComponent:
        workInProgress.type = resolveClassForHotReloading(current.type);
        break;
      case ForwardRef:
        workInProgress.type = resolveForwardRefForHotReloading(current.type);
        break;
      default:
        break;
    }
  }

  return workInProgress;
}

这里波及到的 workInProgress 和 current 两个树通过 alternate 这个指针的相互指引操作来实现首次渲染和非首次渲染的比照更新，保障两个队列都更新而不会失落，并且确保更新始终是 workInProgress 的一部分，这里还做了一个内存缓冲，奇次更新和偶次更新的循环复用

总结

通过学习 React16 对于 Fiber 源码及 React Hooks 的源码，咱们发现整个 React16 的底层外围是基于 Fiber 的优化与扩大，包含 dom-diff 的扩大等，相较于 Vue3 对于 Vue2 的更新，能够看出 React 的优化迭代思路更加充斥对计算机原理底层的思考与发现，当然这两个框架从出发点设计上也是有所不同，Vue 是基于组件级的优化，因此并不需要这样一个 Fiber 的数据结构去构建，但从真正的设计来看 Fiber 的架构设计思维形式的确更加合乎国外程序员的办法与韵味。(ps: 想要理解 Andrew Clark 介绍 Fiber 的同学，能够参看这篇文章 react-fiber-architecure)

参考

  • Hook 简介
  • 【第 2044 期】React Hooks 设计思维
  • 【第 2037 期】React Hooks 实际指南
  • ReactHooks 源码解析之 useEffect
  • react hooks 源码剖析 — useState
  • 分析 React Hooks 底层源码
  • React Hook 的体系设计之一 – 分层
  • React Hooks 的体系设计之二 – 状态粒度
  • React Hooks 的体系设计之三 – 什么是 ref
  • React Hooks 源码解析（译）
  • [[译]深刻 React fiber 架构及源码](https://zhuanlan.zhihu.com/p/…
  • React Fiber 源码解析

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发表至： 前端
2020-08-26
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