I'm still being surprised by the behaviour of
ValueStream :-/
Like, you do this:
newStream = old.map(mapping).shareValue(mapping);
old.add('foo');
newStream.value == 'foo'; // That's not the case
So, unless anyone is listening to the stream, it won't update
.value properly
Or is this problem going to persist
Hi. I've just started implementing the bloc library in my app, and used their example for a form. I've realised this issue: felangel/bloc#1888
Could somebody help me find a solution to do this properly?
So basically, there are events that represent an input field change (
EmailChanged and PasswordChanged events)
To avoid rebuilding the form and doing unnecessary validations, these are debounced:
final debounced = events
.where((event) => event is! FormSubmitted)
.debounceTime(const Duration(milliseconds: 300));
They are then merged with the
FormSubmitted event like this:
return events
.where((event) => event is FormSubmitted)
.mergeWith([debounced])
The problem with that is, that
EmailChangedand PasswordChanged events could be triggered, being debounced, and then the FormSubmitted event could arrive, and be handled before the change events are being handled
This is very rough, and can be improved, but the idea is that any change to either field would reset the sequence to valid = false and would block submit.
final onEmail = PublishSubject<String>(),
onPassword = PublishSubject<String>();
final onSubmit = PublishSubject<bool>();
final email = onEmail.debounceTime(const Duration(seconds: 1)),
password = onPassword.debounceTime(const Duration(seconds: 1));
bool Function(String) validateEmail, validatePassword;
final onSyncInput = Rx.merge([onEmail, onPassword]);
final onValid = Rx.combineLatest2(email.map(validateEmail),
password.map(validatePassword), (e, p) => e && p);
onSyncInput
.switchMap((_) => onValid)
.switchMap((canSubmit) => canSubmit ? onSubmit : Stream.value(false));
But if the AuthUser stream emits another item, which means another user has signed in, i need to automatically make sure the UserProfile stream switches as well
how can i achieve such functionality>
I think I need a way of transforming a stream into another stream, and if the original stream emits another item, the downstream stream needs to see it and change.
So your choice depends, do you only care for the very latest event in the original stream? Then use switchMap. Do you want to handle every event? Use the others, with flatMap, the downstream emits whenever a transformation is completed, with asyncExpand, it will await each transformation and emit.
where i can improve my skills in rxdart
any suggestion
I'd suggest just creating a toy project with rxdart, we have less docs than rxjs for example, but then again, you can always use those docs to help you forward with rxdart, since the api is very similar.
The
statusTransformer() obtains the value (boolean) via an api call for a given username. In some cases, value is already available for a given username and the statusTransformer() not required, When this is the case, I need to somehow update the value inside Map for the username. I may need an appropriate transformer for this but not sure of the type of transformer required. final _streamCtrl = BehaviorSubject<String>();
Stream<Map<String, Future<bool>>> status$;
status$ = __streamCtrl.stream
.transform(transformers.statusTransformer());
statusTransformer() {
return ScanStreamTransformer(
(Map<String, Future<bool>> cache, String username, index) {
cache[username] = _provider.fetchIDataFromApi(username);
return cache;
},
<String, Future<bool>>{},
);
}
Just check
cache.containsKey(username).statusTransformer() {
return ScanStreamTransformer(
(Map<String, Future<bool>> cache, String username, index) {
if (cache.containsKey(username)) {
return cache;
}
cache[username] = _provider.fetchIDataFromApi(username);
return cache;
},
<String, Future<bool>>{},
);
}
@willladislaw if you use
BehaviorSubject you can use the .add(value) method