redux-saga: eventChannel and listener which react callback return - react-native

Question

In react-native backhandler listener react to callback function and act appropriately.
I need to read my store and depending on it, return true or false.
But I cant use select effect in normal function and I cant affect listener callback function from "watchBackButton" function.
export function* backButtonListen() {
return eventChannel(emitter => {
const backHandlerListener = BackHandler.addEventListener(
"hardwareBackPress",
() => {
emitter("back pressed");
}
);
return () => {
backHandlerListener.remove();
};
});
}
export function* watchBackButton() {
const chan = yield call(backButtonListen);
try {
while (true) {
let back = yield take(chan);
}
}

Answer 1

Since event channels are not bidirectional, I don't think there is a way to get some current state from saga to event channel using the select effect.
However, it is possible to access the store directly. There are multiple ways to get the store instance to the event channel. See my other answer here.
Using e.g. the context method you could do something like this:
// redux.js
...
const store = createStore(...);
sagaMiddleware.runSaga(rootSaga, {store});
// root-saga.js
export default function * rootSaga(context) {
yield setContext(context);
yield fork(watchBackButton);
}
// watch-back-button.js
export function* backButtonListen() {
const store = yield getContext('store');
return eventChannel(emitter => {
const backHandlerListener = BackHandler.addEventListener(
"hardwareBackPress",
() => {
emitter("back pressed");
return store.getState().foo === 'bar';
}
);
return () => {
backHandlerListener.remove();
};
});
}
export function* watchBackButton() {
const chan = yield call(backButtonListen);
try {
while (true) {
let back = yield take(chan);
}
}