React source code analysis 13.hooks source code

js_2028 2023-01-25 21:32:00 阅读数:819

reactsourcecodeanalysis13.hooks

hook调用入口

​ 在hook源码中hook存在于Dispatcher中,Dispatcher就是一个对象,不同hook 调用的函数不一样,全局变量ReactCurrentDispatcher.current会根据是mount还是update赋值为HooksDispatcherOnMount或HooksDispatcherOnUpdate

ReactCurrentDispatcher.current =
current === null || current.memoizedState === null//mount or update
? HooksDispatcherOnMount
: HooksDispatcherOnUpdate;
const HooksDispatcherOnMount: Dispatcher = {
//mount时
useCallback: mountCallback,
useContext: readContext,
useEffect: mountEffect,
useImperativeHandle: mountImperativeHandle,
useLayoutEffect: mountLayoutEffect,
useMemo: mountMemo,
useReducer: mountReducer,
useRef: mountRef,
useState: mountState,
//...
};
const HooksDispatcherOnUpdate: Dispatcher = {
//update时
useCallback: updateCallback,
useContext: readContext,
useEffect: updateEffect,
useImperativeHandle: updateImperativeHandle,
useLayoutEffect: updateLayoutEffect,
useMemo: updateMemo,
useReducer: updateReducer,
useRef: updateRef,
useState: updateState,
//...
};

hook数据结构

​ 在FunctionComponent中,多个hook会形成hook链表,保存在Fiber的memoizedState的上,而需要更新的Update保存在hook.queue.pending中

const hook: Hook = {

memoizedState: null,//对于不同hook,有不同的值
baseState: null,//初始state
baseQueue: null,//初始queue队列
queue: null,//需要更新的update
next: null,//下一个hook
};

下面来看下memoizedState对应的值

  • useState:例如const [state, updateState] = useState(initialState),memoizedState等于state的值
  • useReducer:例如const [state, dispatch] = useReducer(reducer, {});,memoizedState等于state的值
  • useEffect:在mountEffect时会调用pushEffect创建effect链表,memoizedState就等于effect链表,effect链表也会挂载到fiber.updateQueue上,每个effect上存在useEffect的第一个参数回调和第二个参数依赖数组,例如,useEffect(callback, [dep]),effect就是{create:callback, dep:dep,…}
  • useRef:例如useRef(0),memoizedState就等于{current: 0}
  • useMemo:例如useMemo(callback, [dep]),memoizedState等于[callback(), dep]
  • useCallback:例如useCallback(callback, [dep]),memoizedState等于[callback, dep].useCallback保存callback函数,useMemo保存callback的执行结果

useState&useReducer

之所以把useState和useReducer放在一起,是因为在源码中useState就是有默认reducer参数的useReducer.

  • useState&useReducer声明

    ​ resolveDispatcher函数会获取当前的Dispatcher

function useState(initialState) {

var dispatcher = resolveDispatcher();
return dispatcher.useState(initialState);
}
function useReducer(reducer, initialArg, init) {

var dispatcher = resolveDispatcher();
return dispatcher.useReducer(reducer, initialArg, init);
}
  • mount阶段

    ​ mount阶段useState调用mountState,useReducer调用mountReducer,唯一区别就是它们创建的queue中lastRenderedReducer不一样,mount有初始值basicStateReducer,所以说useState就是有默认reducer参数的useReducer.

function mountState<S>(//
initialState: (() => S) | S,
): [S, Dispatch<BasicStateAction<S>>] {

const hook = mountWorkInProgressHook();//创建当前hook
if (typeof initialState === 'function') {

initialState = initialState();
}
hook.memoizedState = hook.baseState = initialState;//hook.memoizedState赋值
const queue = (hook.queue = {
//赋值hook.queue
pending: null,
dispatch: null,
lastRenderedReducer: basicStateReducer,//和mountReducer的区别
lastRenderedState: (initialState: any),
});
const dispatch: Dispatch<//创建dispatch函数
BasicStateAction<S>,
> = (queue.dispatch = (dispatchAction.bind(
null,
currentlyRenderingFiber,
queue,
): any));
return [hook.memoizedState, dispatch];//返回memoizedState和dispatch
}
function mountReducer<S, I, A>(
reducer: (S, A) => S,
initialArg: I,
init?: I => S,
): [S, Dispatch<A>] {

const hook = mountWorkInProgressHook();//创建当前hook
let initialState;
if (init !== undefined) {

initialState = init(initialArg);
} else {

initialState = ((initialArg: any): S);
}
hook.memoizedState = hook.baseState = initialState;//hook.memoizedState赋值
const queue = (hook.queue = {
//创建queue
pending: null,
dispatch: null,
lastRenderedReducer: reducer,
lastRenderedState: (initialState: any),
});
const dispatch: Dispatch<A> = (queue.dispatch = (dispatchAction.bind(//创建dispatch函数
null,
currentlyRenderingFiber,
queue,
): any));
return [hook.memoizedState, dispatch];//返回memoizedState和dispatch
}

相关参考视频讲解:进入学习

function basicStateReducer<S>(state: S, action: BasicStateAction<S>): S {

return typeof action === 'function' ? action(state) : action;
}
  • update阶段

    update时会根据hook中的update计算新的state

function updateReducer<S, I, A>(
reducer: (S, A) => S,
initialArg: I,
init?: I => S,
): [S, Dispatch<A>] {

const hook = updateWorkInProgressHook();//获取hook
const queue = hook.queue;
queue.lastRenderedReducer = reducer;
//...更新state和第12章的state计算逻辑基本一致
const dispatch: Dispatch<A> = (queue.dispatch: any);
return [hook.memoizedState, dispatch];
}
  • 执行阶段

    useState执行setState后会调用dispatchAction,dispatchAction做的事情就是讲Update加入queue.pending中,然后开始调度

function dispatchAction(fiber, queue, action) {

var update = {
//创建update
eventTime: eventTime,
lane: lane,
suspenseConfig: suspenseConfig,
action: action,
eagerReducer: null,
eagerState: null,
next: null
};
//queue.pending中加入update
var alternate = fiber.alternate;
if (fiber === currentlyRenderingFiber$1 || alternate !== null && alternate === currentlyRenderingFiber$1) {

//如果是render阶段执行的更新didScheduleRenderPhaseUpdate=true
}
didScheduleRenderPhaseUpdateDuringThisPass = didScheduleRenderPhaseUpdate = true;
} else {

if (fiber.lanes === NoLanes && (alternate === null || alternate.lanes === NoLanes)) {

//如果fiber不存在优先级并且当前alternate不存在或者没有优先级,那就不需要更新了
//优化的步骤
}
scheduleUpdateOnFiber(fiber, lane, eventTime);
}
}

useEffect

  • 声明

    获取并返回useEffect函数

export function useEffect(
create: () => (() => void) | void,
deps: Array<mixed> | void | null,
): void {

const dispatcher = resolveDispatcher();
return dispatcher.useEffect(create, deps);
}
  • mount阶段

    ​ 调用mountEffect,mountEffect调用mountEffectImpl,hook.memoizedState赋值为effect链表

function mountEffectImpl(fiberFlags, hookFlags, create, deps): void {

const hook = mountWorkInProgressHook();//获取hook
const nextDeps = deps === undefined ? null : deps;//依赖
currentlyRenderingFiber.flags |= fiberFlags;//增加flag
hook.memoizedState = pushEffect(//memoizedState=effects环状链表
HookHasEffect | hookFlags,
create,
undefined,
nextDeps,
);
}
  • update阶段

    ​ 浅比较依赖,如果依赖性变了pushEffect第一个参数传HookHasEffect | hookFlags,HookHasEffect表示useEffect依赖项改变了,需要在commit阶段重新执行

function updateEffectImpl(fiberFlags, hookFlags, create, deps): void {

const hook = updateWorkInProgressHook();
const nextDeps = deps === undefined ? null : deps;
let destroy = undefined;
if (currentHook !== null) {

const prevEffect = currentHook.memoizedState;
destroy = prevEffect.destroy;//
if (nextDeps !== null) {

const prevDeps = prevEffect.deps;
if (areHookInputsEqual(nextDeps, prevDeps)) {
//比较deps
//即使依赖相等也要将effect加入链表,以保证顺序一致
pushEffect(hookFlags, create, destroy, nextDeps);
return;
}
}
}
currentlyRenderingFiber.flags |= fiberFlags;
hook.memoizedState = pushEffect(
//参数传HookHasEffect | hookFlags,包含hookFlags的useEffect会在commit阶段执行这个effect
HookHasEffect | hookFlags,
create,
destroy,
nextDeps,
);
}
  • 执行阶段

    ​ 在第9章commit阶段的commitLayoutEffects函数中会调用schedulePassiveEffects,将useEffect的销毁和回调函数push到pendingPassiveHookEffectsUnmount和pendingPassiveHookEffectsMount中,然后在mutation之后调用flushPassiveEffects依次执行上次render的销毁函数回调和本次render 的回调函数

const unmountEffects = pendingPassiveHookEffectsUnmount;
pendingPassiveHookEffectsUnmount = [];
for (let i = 0; i < unmountEffects.length; i += 2) {

const effect = ((unmountEffects[i]: any): HookEffect);
const fiber = ((unmountEffects[i + 1]: any): Fiber);
const destroy = effect.destroy;
effect.destroy = undefined;
if (typeof destroy === 'function') {

try {

destroy();//销毁函数执行
} catch (error) {

captureCommitPhaseError(fiber, error);
}
}
}
const mountEffects = pendingPassiveHookEffectsMount;
pendingPassiveHookEffectsMount = [];
for (let i = 0; i < mountEffects.length; i += 2) {

const effect = ((mountEffects[i]: any): HookEffect);
const fiber = ((mountEffects[i + 1]: any): Fiber);
try {

const create = effect.create;//本次render的创建函数
effect.destroy = create();
} catch (error) {

captureCommitPhaseError(fiber, error);
}
}

useRef

​ sring类型的ref已经不在推荐使用(源码中string会生成refs,发生在coerceRef函数中),ForwardRef只是把ref通过传参传下去,createRef也是{current: any这种结构,所以我们只讨论function或者{current: any}的useRef

//createRef返回{current: any}
export function createRef(): RefObject {

const refObject = {

current: null,
};
return refObject;
}
  • 声明阶段

    ​ 和其他hook一样

export function useRef<T>(initialValue: T): {
|current: T|} {

const dispatcher = resolveDispatcher();
return dispatcher.useRef(initialValue);
}
  • mount阶段

    ​ mount时会调用mountRef,创建hook和ref对象.

function mountRef<T>(initialValue: T): {
|current: T|} {

const hook = mountWorkInProgressHook();//获取useRef
const ref = {
current: initialValue};//ref初始化
hook.memoizedState = ref;
return ref;
}

render阶段:将带有ref属性的Fiber标记上Ref Tag,这一步发生在beginWork和completeWork函数中的markRef

export const Ref = /* */ 0b0000000010000000;
//beginWork中
function markRef(current: Fiber | null, workInProgress: Fiber) {

const ref = workInProgress.ref;
if (
(current === null && ref !== null) ||
(current !== null && current.ref !== ref)
) {

workInProgress.effectTag |= Ref;
}
}
//completeWork中
function markRef(workInProgress: Fiber) {

workInProgress.effectTag |= Ref;
}

commit阶段:

​ 会在commitMutationEffects函数中判断ref是否改变,如果改变了会先执行commitDetachRef先删除之前的ref,然后在commitLayoutEffect中会执行commitAttachRef赋值ref.

function commitMutationEffects(root: FiberRoot, renderPriorityLevel) {

while (nextEffect !== null) {

const effectTag = nextEffect.effectTag;
// ...
if (effectTag & Ref) {

const current = nextEffect.alternate;
if (current !== null) {

commitDetachRef(current);//移除ref
}
}
}
function commitDetachRef(current: Fiber) {

const currentRef = current.ref;
if (currentRef !== null) {

if (typeof currentRef === 'function') {

currentRef(null);//类型是function,则调用
} else {

currentRef.current = null;//否则赋值{current: null}
}
}
}
function commitAttachRef(finishedWork: Fiber) {

const ref = finishedWork.ref;
if (ref !== null) {

const instance = finishedWork.stateNode;//获取ref的实例
let instanceToUse;
switch (finishedWork.tag) {

case HostComponent:
instanceToUse = getPublicInstance(instance);
break;
default:
instanceToUse = instance;
}
if (typeof ref === 'function') {
//ref赋值
ref(instanceToUse);
} else {

ref.current = instanceToUse;
}
}
}
  • update阶段

    ​ update时调用updateRef获取获取当前useRef,然后返回hook链表

function updateRef<T>(initialValue: T): {
|current: T|} {

const hook = updateWorkInProgressHook();//获取当前useRef
return hook.memoizedState;//返回hook链表
}

useMemo&useCallback

  • 声明阶段

    和其他hook 一样

  • mount阶段

    mount阶段useMemo和useCallback唯一区别是在memoizedState中存贮callback还是callback计算出来的函数

function mountMemo<T>(
nextCreate: () => T,
deps: Array<mixed> | void | null,
): T {

const hook = mountWorkInProgressHook();//创建hook
const nextDeps = deps === undefined ? null : deps;
const nextValue = nextCreate();//计算value
hook.memoizedState = [nextValue, nextDeps];//把value和依赖保存在memoizedState中
return nextValue;
}
function mountCallback<T>(callback: T, deps: Array<mixed> | void | null): T {

const hook = mountWorkInProgressHook();//创建hook
const nextDeps = deps === undefined ? null : deps;
hook.memoizedState = [callback, nextDeps];//把callback和依赖保存在memoizedState中
return callback;
}
  • update阶段

    update时也一样,唯一区别就是直接用回调函数还是执行回调后返回的value作为[?, nextDeps]赋值给memoizedState

function updateMemo<T>(
nextCreate: () => T,
deps: Array<mixed> | void | null,
): T {

const hook = updateWorkInProgressHook();//获取hook
const nextDeps = deps === undefined ? null : deps;
const prevState = hook.memoizedState;
if (prevState !== null) {

if (nextDeps !== null) {

const prevDeps: Array<mixed> | null = prevState[1];
if (areHookInputsEqual(nextDeps, prevDeps)) {
//浅比较依赖
return prevState[0];//没变 返回之前的状态
}
}
}
const nextValue = nextCreate();//有变化重新调用callback
hook.memoizedState = [nextValue, nextDeps];
return nextValue;
}
function updateCallback<T>(callback: T, deps: Array<mixed> | void | null): T {

const hook = updateWorkInProgressHook();//获取hook
const nextDeps = deps === undefined ? null : deps;
const prevState = hook.memoizedState;
if (prevState !== null) {

if (nextDeps !== null) {

const prevDeps: Array<mixed> | null = prevState[1];
if (areHookInputsEqual(nextDeps, prevDeps)) {
//浅比较依赖
return prevState[0];//没变 返回之前的状态
}
}
}
hook.memoizedState = [callback, nextDeps];//变了重新将[callback, nextDeps]赋值给memoizedState
return callback;
}

useLayoutEffect

useLayoutEffect和useEffect一样,只是调用的时机不同,它是在commit阶段的commitLayout函数中同步执行

forwardRef

forwardRef也非常简单,就是传递ref属性

export function forwardRef<Props, ElementType: React$ElementType>(
render: (props: Props, ref: React$Ref<ElementType>) => React$Node,
) {

const elementType = {

$$typeof: REACT_FORWARD_REF_TYPE,
render,
};
return elementType;
}
//ForwardRef第二个参数是ref对象
let children = Component(props, secondArg);
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