redux saga yield调用引发错误 类型错误：无法读取 null 的属性"ready"

Question

我有一个应用程序，每次用户登录时都会加载"收藏夹"。数据是使用localforge从IndexedDB加载的。当应用程序重新启动时(在窗口刷新后(，它可以完美地工作。当我注销和登录(root传奇任务正在运行(时，加载"收藏夹"数据的调用抛出错误：

TypeError:无法读取空的属性'ready'

步骤：

export function* handleRecoverFavorites() {
try {
const resp = yield call(localforage.getItem, 'favorites')

传奇代码摘录：

export function* handleRecoverFavorites() {
try {
const resp = yield call(localforage.getItem, 'favorites')
if(resp) {
yield put(recoverFavorites(resp))
yield all(resp.map(symbol => put(getTickPricesSubscribe(symbol))));
}
} catch(err) {
let response={"errorDescr":"Error whilst recovering favorites: "+err}
yield put({ type: types.RESPONSE_ERR, response })
console.log(response.errorDescr)
}  
}

function* runAtStartupSubscirptions(socket, streamSessionId) {
yield fork(send, {"command": "getBalance", "streamSessionId": streamSessionId }, socket );
yield fork(handleRecoverFavorites)
yield fork(handleRecoverCharts)
while(true) {
yield call(delay, STREAMING_PING_TIME)
yield call(send, {"command": "ping", "streamSessionId": streamSessionId }, socket );
} 
}
function* handleRequests(socket) {
let streamSessionId = yield select(state => state.get("auth").get("streamSessionId"))
while(true) {
yield take(types.STREAMING_SOCKET_STATUS)
if(socket.readyState === 1)
yield fork(runAtStartupSubscirptions, socket, streamSessionId)
}
}
export function* handleStreamingConnection() {
let server = yield select(state => state.get("auth").get("server"))
const socket = yield call(createWebSocketConnection, server+"Stream" )
const socketChannel = yield call(createSocketChannel, socket, null)
const task = yield fork(handleRequests, socket)
let channelMsg;
do {
channelMsg = yield take(socketChannel)
if(channelMsg.socketResponse) {
const response = channelMsg.socketResponse;
switch (response.command) {
case "candle":
yield put({ type: types.GET_CANDLES_STREAMING, response })
break;
(...)
default:
console.log("unrequested data: "+response)
}
}
if(channelMsg.socketStatus) {
console.log(channelMsg)
yield put({ type: types.STREAMING_SOCKET_STATUS, channelMsg })
}  
} while (channelMsg.socketStatus!=="Disconnected")
yield cancel(task)
}
export default function* rootSaga() {
while(true) {
// Wait for log-in
yield take(types.LOGIN_SUCCESS);
const handleStreamingtask = yield fork(handleStreamingConnection)
yield take([types.LOGOUT_REQUEST, types.RECONNECTING ])
yield cancel(handleStreamingtask)
const channelMsg={"socketStatus" : "Disconnected"}
yield put({ type: types.STREAMING_SOCKET_STATUS, channelMsg })
}
}

如有任何建议，我将不胜感激。

我添加了console.log行以查看没有传奇调用的结果：

export function* handleRecoverFavorites() {
try {
console.log(localforage.getItem('favorites'))
const resp = yield call(localforage.getItem, 'favorites')

每次Promise返回正确的值：

Promise {<pending>}
__proto__:Promise
[[PromiseStatus]]:"resolved"
[[PromiseValue]]:Array(1)
0:"CHFPLN"
length:1

Answer 1

这就是我解决它的方法，而不是在"yield call"中直接调用localforge方法，我将其封装到单独的类中：

export class LocalDataService {  
getData = ( param ) => {
return localforage.getItem(param)
.then( result => result)
.catch( reason => reason)
}
}
export function* handleRecoverFavorites() {
try {
const api = new LocalDataService()
const resp = yield call( api.getData, 'favorites')
(...)

Answer 2

根据Sylwek的回复，并进一步调查，该问题依赖于内部setItem上下文没有像我们预期的那样绑定。通过使用以下表单调用localforge，我们可以避免创建类：

yield call([localforage, localforage.getItem], 'favorites')

这为我修复了它：(查看传奇文档中的this context部分：https://redux-saga.js.org/docs/basics/DeclarativeEffects/