Issue in writing CBCharacteristic

Question

I am currently working on an BLE app which scans my company beacons , i need to update the values for CBCharacteristic .

I am not getting any error after my write function , but the change does not reflect on BLE device.

I have scanned all CBCharacteristics and then traversing to get particular and calling write function

for (CBCharacteristic* characteristic in beaconCharacteristics)
{
    if ([characteristic.UUID isEqual:[CBUUID UUIDWithString:@"FFF5"]]) {
        [characteristic.service.peripheral writeValue:[@"BeaconE" dataUsingEncoding:NSUTF8StringEncoding] forCharacteristic:characteristic type:CBCharacteristicWriteWithResponse];
    }
}

even i get completion delegate method called after writing without an error

-(void)peripheral:(CBPeripheral *)peripheral didWriteValueForCharacteristic:(CBCharacteristic *)characteristic error:(NSError *)error
{
}

Am i missing anything ? Is it due to hex value ?

Please guide me

Thank you !

Answer 1

It could be that the Characteristic is read only. You can find out by looking at the CBCharacteristicProperties object, which you can get to using characteristic.properties

//Check if the Characteristic is writable
if ((characteristic.properties & CBCharacteristicPropertyWrite) ||
    (characteristic.properties & CBCharacteristicPropertyWriteWithoutResponse))
{
    //Do your Write here
}

Below is a simple method that takes a CBCharacteristicProperties object and logs the properties. . .helps with debugging.

-(void)logCharacteristicProperties:(CBCharacteristicProperties)properties {

    if (properties & CBCharacteristicPropertyBroadcast) {
        NSLog(@"CBCharacteristicPropertyBroadcast");
    }
    if (properties & CBCharacteristicPropertyRead) {
        NSLog(@"CBCharacteristicPropertyRead");
    }
    if (properties & CBCharacteristicPropertyWriteWithoutResponse) {
        NSLog(@"CBCharacteristicPropertyWriteWithoutResponse");
    }
    if (properties & CBCharacteristicPropertyWrite) {
        NSLog(@"CBCharacteristicPropertyWrite");
    }
    if (properties & CBCharacteristicPropertyNotify) {
        NSLog(@"CBCharacteristicPropertyNotify");
    }
    if (properties & CBCharacteristicPropertyIndicate) {
        NSLog(@"CBCharacteristicPropertyIndicate");
    }
    if (properties & CBCharacteristicPropertyAuthenticatedSignedWrites) {
        NSLog(@"CBCharacteristicPropertyAuthenticatedSignedWrites");
    }
    if (properties & CBCharacteristicPropertyExtendedProperties) {
        NSLog(@"CBCharacteristicPropertyExtendedProperties");
    }
    if (properties & CBCharacteristicPropertyNotifyEncryptionRequired) {
        NSLog(@"CBCharacteristicPropertyNotifyEncryptionRequired");
    }
    if (properties & CBCharacteristicPropertyIndicateEncryptionRequired) {
        NSLog(@"CBCharacteristicPropertyIndicateEncryptionRequired");
    }
}

Also, you should be checking for Error to see if CoreBluetooth is throwing an error.

//CBPeripheral Delegate
-(void)peripheral:(CBPeripheral *)peripheral didWriteValueForCharacteristic:(CBCharacteristic *)characteristic error:(NSError *)error {

    if (error) {
        NSLog(@"<error> didWriteValueForCharacteristic %@",[error description]);
        //
        // Add Error handling for failed Writes
        //
    }

    //Add Handling for successful writes

}