I have a function scanAndConnect() that should scan for BLE devices and connect to the device with the specified service ID. This function should be async and should return Future.
The problem is that scanAndConnect() prints 99999 and returns without waiting for flutterReactiveBle.statusStream.listen() to finish although I use await before it.
Future scanAndConnect(Uuid serviceId, Uuid charctId) async {
StreamSubscription<BleStatus>? bleStatusStreamSubscription;
StreamSubscription<DiscoveredDevice>? deviceStreamSubscription;
Stream<DiscoveredDevice> stream;
bleStatusStreamSubscription =
await flutterReactiveBle.statusStream.listen((bleStatus) async {
print("new listen ${bleStatus.toString()}");
if (bleStatus == BleStatus.ready) {
await bleStatusStreamSubscription!.cancel();
connectionStatus = BLEConnectionStatus.Connecting;
stream = await flutterReactiveBle.scanForDevices(
withServices: [serviceId],
scanMode: ScanMode.lowLatency,
);
}
});
print("9999999");
}
....
Future connectToDevice() async {
await ble.scanAndConnect(BLE_SERVICE_UUID, BLE_CHAR_UUID)
print("Statement after await in main");
setState(() {
loading = false;
print("Changing state to ${loading.toString()}");
});
}
This is the output I get in Xcode:
flutter: 9999999
flutter: Statement after await in main
flutter: Changing state to false
flutter: new listen BleStatus.unknown
flutter: new listen BleStatus.ready
How can I make scanAndConnect doesn't return before really finishing?
According to the documentation, FlutterReactiveBle.scanForDevices() returns a Stream, not a Future, so await will not work here. You can use
await for
listen()
await stream.first()
to wait for data from a Stream.
Related
I'm on creating a flutter application with Firebase Cloud Messaging and cloud-functions I'm trying to send notification via FCM with flutter But all what I goit is broadcast received for message in the terminal. and Exception from a finished function: Error: tokens must be a non-empty array in cloud-functions debug
this is my code :
Future<void> configure() async {
await _firebaseMessaging.getToken().then((token) async {
print("FCM: $token");
await _firestore
.collection("flutterTokens")
.doc()
.set({'token': token});
});
}
Future init() async {
final settings = await _requestPermission();
//await _getToken();
await configure();
//await _getToken();
// _registerForegroundMessageHandler();
}
Future<void> _messageHandler(RemoteMessage message) async {
print(
'background message ${message.notification!.body} + ${message.notification!.title}');
}
in the initState():
await _msgService.init();
FirebaseMessaging.onBackgroundMessage(_messageHandler);
I want to connect my Flutter app to bluetooth device with flutter_blue library, and return a result (anything) when the connection is ON. But I don't understand how to do.
Here my code :
Future connect(BluetoothDevice device) async {
_btDevice = device;
StreamSubscription<BluetoothDeviceState> subscription;
subscription = device.state.listen((event) async {
if (event != BluetoothDeviceState.connected) {
await device.connect();
} else {
await device.discoverServices().then((value) => _initFeatures(value));
}
})
..onDone(() {
// Cascade
print("onDone");
});
subscription.asFuture();
//subscription.cancel();
}
And when I call this function with
await newDevice.connect(bluetoothDevice).then((value) => print('OK'));
OK is written before the real connection. _initFeatures if well call when the device is connected.
I try to use asFuture from StreamSubscription with onDone, but that change nothing.
Could you help me please ?
UPDATE 12/10
I've worked on another project for few monthes, and when I come back, I can't solve the problem, so I add the full code.
The concept is a class widget calls the connect future in other class and need to receipt the end of work.
Widget
Future<void> _connectDevice() async {
try {
widget.device.connect(widget.btDevice!).then((value) => _initValue());
} catch (e) {
print(e);
}
}
_initValue() is a method to create the rest of the screen
and the Future connect()
Future connect(BluetoothDevice device) async {
_btDevice = device;
StreamSubscription<BluetoothDeviceState> subscription;
subscription = device.state.listen((event) async {
if (event != BluetoothDeviceState.connected) {
await device.connect();
} else {
await device
.discoverServices()
.then((value) => _initFeatures(value))
.then((value) => print("OK"));
}
});
await subscription.asFuture();
await subscription.cancel();
}
What I'd like is the Future finishes when print("OK") is called, in order .then((value) => _initValue()); is called.
The problem is only this end. Maybe it's not the good way to implement this kind of solution.
I currently have an async function that does the following:
Initializes the stream
Call stream.listen() and provide a function to listen to the stream.
await for the stream to get its first result.
The following is some pseudo code of my function:
Future<void> initStream() async {
// initialize stream
var stream = getStream();
// listen
stream.listen((result) {
// do some stuff here
});
// await until first result
await stream.first; // gives warning
}
Unfortunately it seems that calling stream.first counts as listening to the stream, and streams are not allowed to be listened by multiple...listeners?
I tried a different approach by using await Future.doWhile()
Something like the following:
bool gotFirstResult = false;
Future<void> initStream() async {
var stream = getStream();
stream.listen((result) {
// do some stuff here
gotFirstResult = true;
});
await Future.doWhile(() => !gotFirstResult);
}
This didn't work for me, and I still don't know why. Future.doWhile() was successfully called, but then the function provided to stream.listen() was never called in this case.
Is there a way to wait for the first result of a stream?
(I'm sorry if I didn't describe my question well enough. I'll definitely add other details if needed.)
Thanks in advance!
One way is converting your stream to broadcast one:
var stream = getStream().asBroadcastStream();
stream.listen((result) {
// do some stuff here
});
await stream.first;
Another way, without creating new stream, is to use Completer. It allows you to return a Future which you can complete (send value) later. Caller will be able to await this Future as usual.
Simple example:
Future<int> getValueAsync() {
var completer = Completer<int>();
Future.delayed(Duration(seconds: 1))
.then((_) {
completer.complete(42);
});
return completer.future;
}
is equivalent of
Future<int> getValueAsync() async {
await Future.delayed(Duration(seconds: 1));
return 42;
}
In your case:
Future<void> initStream() {
var stream = getStream();
var firstValueReceived = Completer<void>();
stream.listen((val) {
if (!firstValueReceived.isCompleted) {
firstValueReceived.complete();
}
// do some stuff here
});
return firstValueReceived.future;
}
I recently learned of the fabulous way of waiting for multiple async functions to complete using Future.wait([asyncFuncOne(), asyncFunctwo()])
However, I noticed two different outcomes when running either of these blocks of code. One awaiting each function to finish, the other using Future.wait for parallel processing. What am I doing wrong?
Method 1:
await msm.initProfileData();
await msm.initActivityFeed();
await msm.getRecentlyActiveUsers();
await msm.getRecommendedUsers();
await msm.getGroups();
await msm.getFollowing();
await msm.getFollowers();
Method 2:
await Future.wait([
msm.getFollowing(),
msm.initProfileData(),
msm.initActivityFeed(),
msm.getRecentlyActiveUsers(),
msm.getRecommendedUsers(),
msm.getGroups(),
msm.getFollowers(),
]);
in Method 1, all the async functions complete before my apps home screen appears. In Method 2 the home screen appears before all the async functions complete.
Cheers and thanks in advance.
EDIT: Additional code example.
#override
void initState() {
super.initState();
googleSignIn.onCurrentUserChanged.listen((account) {
handleSignIn(account);
}, onError: (err) {
print('Error signing in: $err');
});
googleSignIn.signInSilently(suppressErrors: false).then((account) {
handleSignIn(account);
}).catchError((err) {
setState(() => _showSignIn = true);
print('Error signing in: $err');
});
}
handleSignIn(GoogleSignInAccount account) async {
if (account != null) {
await createUserInFirestore();
setState(() {
isAuth = true;
});
} else {
setState(() {
isAuth = false;
_showSignIn = true;
});
}
}
createUserInFirestore() async {
final GoogleSignInAccount user = googleSignIn.currentUser;
DocumentSnapshot doc = await usersRef.document(user.id).get();
//...
//do stuff
//...
await someFunc1(); //Method1
// await comeFunc2(); //Method2
//do more stuff
}
someFunc1() async {
msm.asyncfunc1();
msm.asyncfunc2();
}
someFunc2() async {
await Future.wait([
msm.asyncFunc1(),
msm.asyncFunc2(),
]);
}
#override
Widget build(BuildContext context) {
return isAuth ? buildAuthScreen() : buildUnAuthScreen();
}
Using Future.wait(List<Future>) will wait for all the async operations without sequence as mentioned in the docs. While using await consecutively, it'll wait for the first await async operation to finish before running the next await async operation. If you have a prerequisite output before running the next async operation, it's better to use await async in sequence instead.
I am updating my document with this code.
Future<void> save() async {
print('league save');
final DocumentReference ref =
Firestore.instance.collection('leagues').document(_documentName);
Firestore.instance.runTransaction((Transaction tx) async {
DocumentSnapshot postSnapshot = await tx.get(ref);
if (postSnapshot.exists) {
await tx.update(ref, _getDocument());
print('league save complete');
}
});
}
I believe that this may be failing sometimes but I am not sure. I am got getting an error.
The reason I suspect it is failing sometimes is because my listener (elsewhere in the app) isn't always getting fired when the document changes.
How do I log or capture an error in the transaction?
runTransaction is just a normal async operation that you can follow up with a then and catchError:
Firestore.instance.runTransaction((Transaction tx) async {
// do whatever
}).then((val) {
// do something upon success
}).catchError((e) {
// do something upon error
});
and you can skip then .then() if you want