简介
react-redux是 Redux 官方提供的 React 绑定库，它的作用只有一个：让 React 组件能够方便地读取 Redux 的状态，并在状态变化时自动刷新
connect
是通过函数createConnect调用返回的connect
createConnect默认参数有
connectHOC：connectAdvancedmapStateToPropsFactories：defaultMapStateToPropsFactoriesmapDispatchToPropsFactories：defaultMapDispatchToPropsFactoriesmergePropsFactories：defaultSelectorFactory
connect函数返回值是connectAdvanced的返回值，其返回值为函数
function wrapWithConnect(WrappedComponent)
javascript
function connect(
mapStateToProps,
mapDispatchToProps,
mergeProps,
{
pure = true,
areStatesEqual = strictEqual,
areOwnPropsEqual = shallowEqual,
areStatePropsEqual = shallowEqual,
areMergedPropsEqual = shallowEqual,
...extraOptions
} = {}
) {
const initMapStateToProps = match(
mapStateToProps,
mapStateToPropsFactories,
'mapStateToProps'
)
const initMapDispatchToProps = match(
mapDispatchToProps,
mapDispatchToPropsFactories,
'mapDispatchToProps'
)
const initMergeProps = match(mergeProps, mergePropsFactories, 'mergeProps')
return connectHOC(selectorFactory, {
// used in error messages
methodName: 'connect',
// used to compute Connect's displayName from the wrapped component's displayName.
getDisplayName: (name) => `Connect(${name})`,
// if mapStateToProps is falsy, the Connect component doesn't subscribe to store state changes
shouldHandleStateChanges: Boolean(mapStateToProps),
// passed through to selectorFactory
initMapStateToProps,
initMapDispatchToProps,
initMergeProps,
pure,
areStatesEqual,
areOwnPropsEqual,
areStatePropsEqual,
areMergedPropsEqual,
// any extra options args can override defaults of connect or connectAdvanced
...extraOptions,
})
}
export default function connectAdvanced(
/*
selectorFactory is a func that is responsible for returning the selector function used to
compute new props from state, props, and dispatch. For example:
export default connectAdvanced((dispatch, options) => (state, props) => ({
thing: state.things[props.thingId],
saveThing: fields => dispatch(actionCreators.saveThing(props.thingId, fields)),
}))(YourComponent)
Access to dispatch is provided to the factory so selectorFactories can bind actionCreators
outside of their selector as an optimization. Options passed to connectAdvanced are passed to
the selectorFactory, along with displayName and WrappedComponent, as the second argument.
Note that selectorFactory is responsible for all caching/memoization of inbound and outbound
props. Do not use connectAdvanced directly without memoizing results between calls to your
selector, otherwise the Connect component will re-render on every state or props change.
*/
selectorFactory,
// options object:
{
// the func used to compute this HOC's displayName from the wrapped component's displayName.
// probably overridden by wrapper functions such as connect()
getDisplayName = (name) => `ConnectAdvanced(${name})`,
// shown in error messages
// probably overridden by wrapper functions such as connect()
methodName = 'connectAdvanced',
// REMOVED: if defined, the name of the property passed to the wrapped element indicating the number of
// calls to render. useful for watching in react devtools for unnecessary re-renders.
renderCountProp = undefined,
// determines whether this HOC subscribes to store changes
shouldHandleStateChanges = true,
// REMOVED: the key of props/context to get the store
storeKey = 'store',
// REMOVED: expose the wrapped component via refs
withRef = false,
// use React's forwardRef to expose a ref of the wrapped component
forwardRef = false,
// the context consumer to use
context = ReactReduxContext,
// additional options are passed through to the selectorFactory
...connectOptions
} = {}
) {
if (process.env.NODE_ENV !== 'production') {
if (renderCountProp !== undefined) {
throw new Error(
`renderCountProp is removed. render counting is built into the latest React Dev Tools profiling extension`
)
}
if (withRef) {
throw new Error(
'withRef is removed. To access the wrapped instance, use a ref on the connected component'
)
}
const customStoreWarningMessage =
'To use a custom Redux store for specific components, create a custom React context with ' +
"React.createContext(), and pass the context object to React Redux's Provider and specific components" +
' like: <Provider context={MyContext}><ConnectedComponent context={MyContext} /></Provider>. ' +
'You may also pass a {context : MyContext} option to connect'
if (storeKey !== 'store') {
throw new Error(
'storeKey has been removed and does not do anything. ' +
customStoreWarningMessage
)
}
}
const Context = context
return function wrapWithConnect(WrappedComponent) {
if (
process.env.NODE_ENV !== 'production' &&
!isValidElementType(WrappedComponent)
) {
throw new Error(
`You must pass a component to the function returned by ` +
`${methodName}. Instead received ${stringifyComponent(
WrappedComponent
)}`
)
}
const wrappedComponentName =
WrappedComponent.displayName || WrappedComponent.name || 'Component'
const displayName = getDisplayName(wrappedComponentName)
const selectorFactoryOptions = {
...connectOptions,
getDisplayName,
methodName,
renderCountProp,
shouldHandleStateChanges,
storeKey,
displayName,
wrappedComponentName,
WrappedComponent,
}
const { pure } = connectOptions
function createChildSelector(store) {
return selectorFactory(store.dispatch, selectorFactoryOptions)
}
// If we aren't running in "pure" mode, we don't want to memoize values.
// To avoid conditionally calling hooks, we fall back to a tiny wrapper
// that just executes the given callback immediately.
const usePureOnlyMemo = pure ? useMemo : (callback) => callback()
function ConnectFunction(props) {
const [
propsContext,
reactReduxForwardedRef,
wrapperProps,
] = useMemo(() => {
// Distinguish between actual "data" props that were passed to the wrapper component,
// and values needed to control behavior (forwarded refs, alternate context instances).
// To maintain the wrapperProps object reference, memoize this destructuring.
const { reactReduxForwardedRef, ...wrapperProps } = props
return [props.context, reactReduxForwardedRef, wrapperProps]
}, [props])
const ContextToUse = useMemo(() => {
// Users may optionally pass in a custom context instance to use instead of our ReactReduxContext.
// Memoize the check that determines which context instance we should use.
return propsContext &&
propsContext.Consumer &&
isContextConsumer(<propsContext.Consumer />)
? propsContext
: Context
}, [propsContext, Context])
// Retrieve the store and ancestor subscription via context, if available
const contextValue = useContext(ContextToUse)
// The store _must_ exist as either a prop or in context.
// We'll check to see if it _looks_ like a Redux store first.
// This allows us to pass through a `store` prop that is just a plain value.
const didStoreComeFromProps =
Boolean(props.store) &&
Boolean(props.store.getState) &&
Boolean(props.store.dispatch)
const didStoreComeFromContext =
Boolean(contextValue) && Boolean(contextValue.store)
if (
process.env.NODE_ENV !== 'production' &&
!didStoreComeFromProps &&
!didStoreComeFromContext
) {
throw new Error(
`Could not find "store" in the context of ` +
`"${displayName}". Either wrap the root component in a <Provider>, ` +
`or pass a custom React context provider to <Provider> and the corresponding ` +
`React context consumer to ${displayName} in connect options.`
)
}
// Based on the previous check, one of these must be true
const store = didStoreComeFromProps ? props.store : contextValue.store
const childPropsSelector = useMemo(() => {
// The child props selector needs the store reference as an input.
// Re-create this selector whenever the store changes.
return createChildSelector(store)
}, [store])
const [subscription, notifyNestedSubs] = useMemo(() => {
if (!shouldHandleStateChanges) return NO_SUBSCRIPTION_ARRAY
// This Subscription's source should match where store came from: props vs. context. A component
// connected to the store via props shouldn't use subscription from context, or vice versa.
const subscription = new Subscription(
store,
didStoreComeFromProps ? null : contextValue.subscription
)
// `notifyNestedSubs` is duplicated to handle the case where the component is unmounted in
// the middle of the notification loop, where `subscription` will then be null. This can
// probably be avoided if Subscription's listeners logic is changed to not call listeners
// that have been unsubscribed in the middle of the notification loop.
const notifyNestedSubs = subscription.notifyNestedSubs.bind(
subscription
)
return [subscription, notifyNestedSubs]
}, [store, didStoreComeFromProps, contextValue])
// Determine what {store, subscription} value should be put into nested context, if necessary,
// and memoize that value to avoid unnecessary context updates.
const overriddenContextValue = useMemo(() => {
if (didStoreComeFromProps) {
// This component is directly subscribed to a store from props.
// We don't want descendants reading from this store - pass down whatever
// the existing context value is from the nearest connected ancestor.
return contextValue
}
// Otherwise, put this component's subscription instance into context, so that
// connected descendants won't update until after this component is done
return {
...contextValue,
subscription,
}
}, [didStoreComeFromProps, contextValue, subscription])
// We need to force this wrapper component to re-render whenever a Redux store update
// causes a change to the calculated child component props (or we caught an error in mapState)
const [
[previousStateUpdateResult],
forceComponentUpdateDispatch,
] = useReducer(storeStateUpdatesReducer, EMPTY_ARRAY, initStateUpdates)
// Propagate any mapState/mapDispatch errors upwards
if (previousStateUpdateResult && previousStateUpdateResult.error) {
throw previousStateUpdateResult.error
}
// Set up refs to coordinate values between the subscription effect and the render logic
const lastChildProps = useRef()
const lastWrapperProps = useRef(wrapperProps)
const childPropsFromStoreUpdate = useRef()
const renderIsScheduled = useRef(false)
const actualChildProps = usePureOnlyMemo(() => {
// Tricky logic here:
// - This render may have been triggered by a Redux store update that produced new child props
// - However, we may have gotten new wrapper props after that
// If we have new child props, and the same wrapper props, we know we should use the new child props as-is.
// But, if we have new wrapper props, those might change the child props, so we have to recalculate things.
// So, we'll use the child props from store update only if the wrapper props are the same as last time.
if (
childPropsFromStoreUpdate.current &&
wrapperProps === lastWrapperProps.current
) {
return childPropsFromStoreUpdate.current
}
// TODO We're reading the store directly in render() here. Bad idea?
// This will likely cause Bad Things (TM) to happen in Concurrent Mode.
// Note that we do this because on renders _not_ caused by store updates, we need the latest store state
// to determine what the child props should be.
return childPropsSelector(store.getState(), wrapperProps)
}, [store, previousStateUpdateResult, wrapperProps])
// We need this to execute synchronously every time we re-render. However, React warns
// about useLayoutEffect in SSR, so we try to detect environment and fall back to
// just useEffect instead to avoid the warning, since neither will run anyway.
useIsomorphicLayoutEffectWithArgs(captureWrapperProps, [
lastWrapperProps,
lastChildProps,
renderIsScheduled,
wrapperProps,
actualChildProps,
childPropsFromStoreUpdate,
notifyNestedSubs,
])
// Our re-subscribe logic only runs when the store/subscription setup changes
useIsomorphicLayoutEffectWithArgs(
subscribeUpdates,
[
shouldHandleStateChanges,
store,
subscription,
childPropsSelector,
lastWrapperProps,
lastChildProps,
renderIsScheduled,
childPropsFromStoreUpdate,
notifyNestedSubs,
forceComponentUpdateDispatch,
],
[store, subscription, childPropsSelector]
)
// Now that all that's done, we can finally try to actually render the child component.
// We memoize the elements for the rendered child component as an optimization.
const renderedWrappedComponent = useMemo(
() => (
<WrappedComponent
{...actualChildProps}
ref={reactReduxForwardedRef}
/>
),
[reactReduxForwardedRef, WrappedComponent, actualChildProps]
)
// If React sees the exact same element reference as last time, it bails out of re-rendering
// that child, same as if it was wrapped in React.memo() or returned false from shouldComponentUpdate.
const renderedChild = useMemo(() => {
if (shouldHandleStateChanges) {
// If this component is subscribed to store updates, we need to pass its own
// subscription instance down to our descendants. That means rendering the same
// Context instance, and putting a different value into the context.
return (
<ContextToUse.Provider value={overriddenContextValue}>
{renderedWrappedComponent}
</ContextToUse.Provider>
)
}
return renderedWrappedComponent
}, [ContextToUse, renderedWrappedComponent, overriddenContextValue])
return renderedChild
}
// If we're in "pure" mode, ensure our wrapper component only re-renders when incoming props have changed.
const Connect = pure ? React.memo(ConnectFunction) : ConnectFunction
Connect.WrappedComponent = WrappedComponent
Connect.displayName = ConnectFunction.displayName = displayName
if (forwardRef) {
const forwarded = React.forwardRef(function forwardConnectRef(
props,
ref
) {
return <Connect {...props} reactReduxForwardedRef={ref} />
})
forwarded.displayName = displayName
forwarded.WrappedComponent = WrappedComponent
return hoistStatics(forwarded, WrappedComponent)
}
return hoistStatics(Connect, WrappedComponent)
}
}wrapWithConnect的处理流程为
- 定义
createChildSelector函数，内部调用selectorFactory - 定义
ConnectFunction
javascript
function wrapWithConnect(WrappedComponent) {
if (
process.env.NODE_ENV !== 'production' &&
!isValidElementType(WrappedComponent)
) {
throw new Error(
`You must pass a component to the function returned by ` +
`${methodName}. Instead received ${stringifyComponent(
WrappedComponent
)}`
)
}
const wrappedComponentName =
WrappedComponent.displayName || WrappedComponent.name || 'Component'
const displayName = getDisplayName(wrappedComponentName)
const selectorFactoryOptions = {
...connectOptions,
getDisplayName,
methodName,
renderCountProp,
shouldHandleStateChanges,
storeKey,
displayName,
wrappedComponentName,
WrappedComponent,
}
const { pure } = connectOptions
function createChildSelector(store) {
return selectorFactory(store.dispatch, selectorFactoryOptions)
}
// If we aren't running in "pure" mode, we don't want to memoize values.
// To avoid conditionally calling hooks, we fall back to a tiny wrapper
// that just executes the given callback immediately.
const usePureOnlyMemo = pure ? useMemo : (callback) => callback()
function ConnectFunction(props) {
const [
propsContext,
reactReduxForwardedRef,
wrapperProps,
] = useMemo(() => {
// Distinguish between actual "data" props that were passed to the wrapper component,
// and values needed to control behavior (forwarded refs, alternate context instances).
// To maintain the wrapperProps object reference, memoize this destructuring.
const { reactReduxForwardedRef, ...wrapperProps } = props
return [props.context, reactReduxForwardedRef, wrapperProps]
}, [props])
const ContextToUse = useMemo(() => {
// Users may optionally pass in a custom context instance to use instead of our ReactReduxContext.
// Memoize the check that determines which context instance we should use.
return propsContext &&
propsContext.Consumer &&
isContextConsumer(<propsContext.Consumer />)
? propsContext
: Context
}, [propsContext, Context])
// Retrieve the store and ancestor subscription via context, if available
const contextValue = useContext(ContextToUse)
// The store _must_ exist as either a prop or in context.
// We'll check to see if it _looks_ like a Redux store first.
// This allows us to pass through a `store` prop that is just a plain value.
const didStoreComeFromProps =
Boolean(props.store) &&
Boolean(props.store.getState) &&
Boolean(props.store.dispatch)
const didStoreComeFromContext =
Boolean(contextValue) && Boolean(contextValue.store)
if (
process.env.NODE_ENV !== 'production' &&
!didStoreComeFromProps &&
!didStoreComeFromContext
) {
throw new Error(
`Could not find "store" in the context of ` +
`"${displayName}". Either wrap the root component in a <Provider>, ` +
`or pass a custom React context provider to <Provider> and the corresponding ` +
`React context consumer to ${displayName} in connect options.`
)
}
// Based on the previous check, one of these must be true
const store = didStoreComeFromProps ? props.store : contextValue.store
const childPropsSelector = useMemo(() => {
// The child props selector needs the store reference as an input.
// Re-create this selector whenever the store changes.
return createChildSelector(store)
}, [store])
const [subscription, notifyNestedSubs] = useMemo(() => {
if (!shouldHandleStateChanges) return NO_SUBSCRIPTION_ARRAY
// This Subscription's source should match where store came from: props vs. context. A component
// connected to the store via props shouldn't use subscription from context, or vice versa.
const subscription = new Subscription(
store,
didStoreComeFromProps ? null : contextValue.subscription
)
// `notifyNestedSubs` is duplicated to handle the case where the component is unmounted in
// the middle of the notification loop, where `subscription` will then be null. This can
// probably be avoided if Subscription's listeners logic is changed to not call listeners
// that have been unsubscribed in the middle of the notification loop.
const notifyNestedSubs = subscription.notifyNestedSubs.bind(
subscription
)
return [subscription, notifyNestedSubs]
}, [store, didStoreComeFromProps, contextValue])
// Determine what {store, subscription} value should be put into nested context, if necessary,
// and memoize that value to avoid unnecessary context updates.
const overriddenContextValue = useMemo(() => {
if (didStoreComeFromProps) {
// This component is directly subscribed to a store from props.
// We don't want descendants reading from this store - pass down whatever
// the existing context value is from the nearest connected ancestor.
return contextValue
}
// Otherwise, put this component's subscription instance into context, so that
// connected descendants won't update until after this component is done
return {
...contextValue,
subscription,
}
}, [didStoreComeFromProps, contextValue, subscription])
// We need to force this wrapper component to re-render whenever a Redux store update
// causes a change to the calculated child component props (or we caught an error in mapState)
const [
[previousStateUpdateResult],
forceComponentUpdateDispatch,
] = useReducer(storeStateUpdatesReducer, EMPTY_ARRAY, initStateUpdates)
// Propagate any mapState/mapDispatch errors upwards
if (previousStateUpdateResult && previousStateUpdateResult.error) {
throw previousStateUpdateResult.error
}
// Set up refs to coordinate values between the subscription effect and the render logic
const lastChildProps = useRef()
const lastWrapperProps = useRef(wrapperProps)
const childPropsFromStoreUpdate = useRef()
const renderIsScheduled = useRef(false)
const actualChildProps = usePureOnlyMemo(() => {
// Tricky logic here:
// - This render may have been triggered by a Redux store update that produced new child props
// - However, we may have gotten new wrapper props after that
// If we have new child props, and the same wrapper props, we know we should use the new child props as-is.
// But, if we have new wrapper props, those might change the child props, so we have to recalculate things.
// So, we'll use the child props from store update only if the wrapper props are the same as last time.
if (
childPropsFromStoreUpdate.current &&
wrapperProps === lastWrapperProps.current
) {
return childPropsFromStoreUpdate.current
}
// TODO We're reading the store directly in render() here. Bad idea?
// This will likely cause Bad Things (TM) to happen in Concurrent Mode.
// Note that we do this because on renders _not_ caused by store updates, we need the latest store state
// to determine what the child props should be.
return childPropsSelector(store.getState(), wrapperProps)
}, [store, previousStateUpdateResult, wrapperProps])
// We need this to execute synchronously every time we re-render. However, React warns
// about useLayoutEffect in SSR, so we try to detect environment and fall back to
// just useEffect instead to avoid the warning, since neither will run anyway.
useIsomorphicLayoutEffectWithArgs(captureWrapperProps, [
lastWrapperProps,
lastChildProps,
renderIsScheduled,
wrapperProps,
actualChildProps,
childPropsFromStoreUpdate,
notifyNestedSubs,
])
// Our re-subscribe logic only runs when the store/subscription setup changes
useIsomorphicLayoutEffectWithArgs(
subscribeUpdates,
[
shouldHandleStateChanges,
store,
subscription,
childPropsSelector,
lastWrapperProps,
lastChildProps,
renderIsScheduled,
childPropsFromStoreUpdate,
notifyNestedSubs,
forceComponentUpdateDispatch,
],
[store, subscription, childPropsSelector]
)
// Now that all that's done, we can finally try to actually render the child component.
// We memoize the elements for the rendered child component as an optimization.
const renderedWrappedComponent = useMemo(
() => (
<WrappedComponent
{...actualChildProps}
ref={reactReduxForwardedRef}
/>
),
[reactReduxForwardedRef, WrappedComponent, actualChildProps]
)
// If React sees the exact same element reference as last time, it bails out of re-rendering
// that child, same as if it was wrapped in React.memo() or returned false from shouldComponentUpdate.
const renderedChild = useMemo(() => {
if (shouldHandleStateChanges) {
// If this component is subscribed to store updates, we need to pass its own
// subscription instance down to our descendants. That means rendering the same
// Context instance, and putting a different value into the context.
return (
<ContextToUse.Provider value={overriddenContextValue}>
{renderedWrappedComponent}
</ContextToUse.Provider>
)
}
return renderedWrappedComponent
}, [ContextToUse, renderedWrappedComponent, overriddenContextValue])
return renderedChild
}
// If we're in "pure" mode, ensure our wrapper component only re-renders when incoming props have changed.
const Connect = pure ? React.memo(ConnectFunction) : ConnectFunction
Connect.WrappedComponent = WrappedComponent
Connect.displayName = ConnectFunction.displayName = displayName
if (forwardRef) {
const forwarded = React.forwardRef(function forwardConnectRef(
props,
ref
) {
return <Connect {...props} reactReduxForwardedRef={ref} />
})
forwarded.displayName = displayName
forwarded.WrappedComponent = WrappedComponent
return hoistStatics(forwarded, WrappedComponent)
}
return hoistStatics(Connect, WrappedComponent)
}wrapMapToPropsFunc
在处理属性和分发映射时使用到了wrapMapToPropsFunc函数创建代理
- 定义proxy对象，设置属性
dependsOnOwnProps为true，首次mapToProps处理函数为detectFactoryAndVerify - 在后序调用时使用的是用户指定的
mapToProps以及重新设置属性dependsOnOwnProps,如果mapToProps返回的类型为函数，则重新设置代理的mapToProps和dependsOnOwnProps
javascript
export function wrapMapToPropsFunc(mapToProps, methodName) {
return function initProxySelector(dispatch, { displayName }) {
const proxy = function mapToPropsProxy(stateOrDispatch, ownProps) {
return proxy.dependsOnOwnProps
? proxy.mapToProps(stateOrDispatch, ownProps)
: proxy.mapToProps(stateOrDispatch)
}
// allow detectFactoryAndVerify to get ownProps
proxy.dependsOnOwnProps = true
proxy.mapToProps = function detectFactoryAndVerify(
stateOrDispatch,
ownProps
) {
proxy.mapToProps = mapToProps
proxy.dependsOnOwnProps = getDependsOnOwnProps(mapToProps)
let props = proxy(stateOrDispatch, ownProps)
if (typeof props === 'function') {
proxy.mapToProps = props
proxy.dependsOnOwnProps = getDependsOnOwnProps(props)
props = proxy(stateOrDispatch, ownProps)
}
if (process.env.NODE_ENV !== 'production')
verifyPlainObject(props, displayName, methodName)
return props
}
return proxy
}
}