Support concurrent characteristic reads via Future.wait about flutter_blue

[jack4git]

Tried this again after I learned some lessons about async ... another version of the code (device is a BluetoothDevice). Based on logs from flutter_blue, all the characteristics are getting read, no errors being caught, it looks like one or more Futures just don't return.

Could also be my code or a Dart issue!

Future.wait(_charValMap.keys.map(powerDevice.scanResult.device.readCharacteristic))
  .then((List<List<int>> listList) {
    print('Inside Future.wait, listList has ${listList.length} elements');
  })
  .catchError((e) {
    print('error $e');
  }); 

[pauldemarco]

I'll have some time to investigate this next week, thanks for reporting!

[pauldemarco]

Future.wait will fire off the functions in quick succession.

Both iOS and Android only support one readCharacteristic attempt at a time, or in other words, you must wait for the readCharacteristic to return before calling it again.

Dart makes this easy with async functions like so:

readAll() async {
  final value1 = await device.readCharacteristic(char1);
  final value2 = await device.readCharacteristic(char2);
  // do something with value1 and value2
}

Here, the await keyword will wait for readCharacteristic to return before moving onto the next line of code.

If you wanted similar functionality to your function you could do something like:

Future<List> readAll() async {
  final value1 = await device.readCharacteristic(char1);
  final value2 = await device.readCharacteristic(char2);
  return [value1, value2];
}

readAll().then((values) => print('${values.length} read.'));

[jack4git]

re: one attempt at a time ... I was not aware of the limitation in iOS / Android, can you point me at a reference? (It might actually be a BLE limitation -- I write embedded BLE firmware also and this might be a spec thing ...)

re: firing off in quick succession, yes indeed. But based on what I'm seeing logged, it looks like flutter_blue is actually executing all the reads successfully ... the log looks just like it does on my successful approach using await in a loop ... I wonder if the right solution here is (assuming you can detect multiple overlapping read attempts) is to error out, or to actually allow it to work (sequentially) by returning futures for all requests when they complete ... right now it almost "succeeds silently" ...

Here's my current approach, given that flutter_blue gives me lists of characteristics: looping through a list (this just does the bluetooth value to internal model mapping on one characteristic at the moment):

for (BluetoothCharacteristic char in _charValMap.keys.toList()) {
    tmpIntList = await powerDevice.scanResult.device.readCharacteristic(char);
    _charValMap[char] = tmpIntList;
    print('processed _charValMap item: ${char.uuid} ${tmpIntList.toString()}');
    // Process/save values here ...
  }

[pauldemarco]

I am unable to replicate this issue @jack4git

Closing this for now, please reopen if you are still experiencing this in the latest version.

[akshay-kapase]

There are three services out of which the third one should be used to read and write characteristic.The first two are generic and the third one is custom service using which it will work. Try this :

_scanResult.device.discoverServices().then((services){
services[2].characteristics[0].read();
});