didUpdateValueForCharacteristic event failing

[shanith32]

We are working on a BLE app that acts as a Central and connects to a chip(peripheral). The peripheral contains a service and a characteristic and the characteristic contains a notify property. After calling peripheral.subscribeToCharacteristic() and peripheral.readValueForCharacteristic() methods, it subscribes successfully with the didUpdateNotificationStateForCharacteristics event, however errors out on the didUpdateValueForCharacteristic event. The error message is: 257: failed to initiate reading characteristic for peripheral name

[m1ga]

searching for the error message I guess you are trying to implement it on Android, right?
Run your app with --log-level debug to see some more logs.

It should show you:

Log.d(LCAT, "readValueForCharacteristic(): characteristic- " + characteristicProxy.uuid()
						+ " read initiation status- ." + isReadInitiated);

(source)

with false as isReadInitiated. According to https://stackoverflow.com/a/30720262/5193915 it could be a timing issue. Did you have a look at the examples in https://github.com/tidev/appcelerator.ble/tree/master/example how they do the flow?

[shanith32]

@m1ga Thank you for the above information. I ran a build with --log-level debug and found this,
[DEBUG] TiBleCentralOperationManager: readValueForCharacteristic(): characteristic- 4aa10003-d92d-48d3-b522-509b8524ac31 read initiation status- .false

We cloned the centralManager.js and peripheralChannel.js files from the example and nothing much is changed on them.

Here's where the error occurs on the peripheralChannel.js

appcelerator.ble/example/peripheralChannel.js

Line 215 in ff1591f

alert('Error while didUpdateValueForCharacteristic' + e.errorCode + '/' + e.errorDomain + '/' + e.errorDescription);

The BLE chip(peripheral) that we are connecting to only has a notify property on its characteristic, so maybe calling peripheral.readValueForCharacteristic() on line

appcelerator.ble/example/peripheralChannel.js

Line 388 in ff1591f

peripheral.readValueForCharacteristic({

is the problem. If that is the case would you be able to let me know which method to call/event to listen to access data streamed with a characteristic's notify property? Appreciate your help!

[m1ga]

have a look at this code:

cmgr.addEventListener('didDiscoverPeripheral', function(e) {
	cmgr.connectPeripheral({
		peripheral: e.peripheral,
		options: {
			[BLE.CONNECT_PERIPHERAL_OPTIONS_KEY_NOTIFY_ON_CONNECTION]: true,
			[BLE.CONNECT_PERIPHERAL_OPTIONS_KEY_NOTIFY_ON_DISCONNECTION]: true
		}
	});
});

cmgr.addEventListener('didConnectPeripheral', function(e) {
	peripheral = e.peripheral;

	peripheral.addEventListener('didDiscoverServices', function(e) {
		var services = e.source.services;

		services.forEach(function(service) {
			if (service.uuid.toUpperCase() == 'DEVICE_UUID') {
				e.source.discoverCharacteristics({
					characteristics: [],
					service: service
				});
			}
		});

		peripheral.addEventListener('didDiscoverCharacteristics', function(e) {
			var peripheral = e.peripheral;
			var characteristics = e.service.characteristics;

			characteristics.forEach(function(characteristic) {

				function _didUpdateValueForCharacteristic(e) {}
				function _didReadValue(e) {}

				if (characteristic.uuid == 'CHAR_UUID') {
					global.charactersticObject = characteristic;

					peripheral.subscribeToCharacteristic({
						characteristic: characteristic,
						descriptorUUID: BLE.CBUUID_CLIENT_CHARACTERISTIC_CONFIGURATION_STRING,
						descriptorValue: BLE.ENABLE_NOTIFICATION_VALUE
					});

					peripheral.readValueForCharacteristic(characteristic);
					peripheral.addEventListener('didReadValueForCharacteristic', _didReadValue);
					peripheral.addEventListener('didUpdateValueForCharacteristic', _didUpdateValueForCharacteristic);
				}
			});
		});
		peripheral.addEventListener('didUpdateValueForCharacteristic', function(e) {});

		peripheral.discoverServices();
	});
});

cmgr.startScan();

I had that in an example file. That should be the correct flow