Cannot read BLE Characterstic from Android

Question

Important to note, I am using Xamarin to develop Cross-platform apps. For bluetooth I have to develop platform specfic, therefore the following code is all part of the android library, but coded in C#, since that is the language of xamarin. It is relatively easy to understand, even if you do not know C# or Xamarin.

My problem is very similiar to this one, with the difference that I am completely sure that I have permission to read, since it does work from iOS.

I work with a BLE heart rate monitor. I connect to it, then set notifications for the heart rate characteristic and then read it. From iOS this works perfectly fine. From android however it tells me I do not have the permissions to read the characterstic. This is obviously wrong, since it works from iOS. What could be the cause here? Do I maybe need to reload the permissions after connecting to a device? I didn't find a function for that.

This is the code I use to connect to the device.

bleGatt = device.ConnectGatt(Android.App.Application.Context, false, new MyGattCallback(this));

Then in the connection status changed I start service discovery. The handleConnectionSuccess() and handleDisconnect() go back to the UI to show the progress to the user.

public override void OnConnectionStateChange(BluetoothGatt gatt, 
            [GeneratedEnum] GattStatus status, [GeneratedEnum] ProfileState newState)
{
    switch(newState)
    {
    case ProfileState.Connected:
        reference.handleConnectionSuccess();
        gatt.DiscoverServices();
        break;
    case ProfileState.Disconnected:
        reference.handleDisconnect();
        break;
    }
}

public override void OnServicesDiscovered(BluetoothGatt gatt, [GeneratedEnum] GattStatus status)
{
    if (status == GattStatus.Success) {
        BluetoothGattService service = bleGatt.GetService(UUID.FromString("CDEACB80-5235-4C07-8846-93A37EE6B86D"));
        if (service == null)
            return;
        BluetoothGattCharacteristic characteristic = service.GetCharacteristic(UUID.FromString("CDEACB80-5235-4C07-8846-93A37EE6B86D"));
        bleGatt.SetCharacteristicNotification(characteristic, true);
        bool readable = ((characteristic.Permissions & GattPermission.Read) != 0);
        Debug.WriteLine("Characteristic is readable: " + readable + " Permissions: " + characteristic.Permissions);
    } else 
        Debug.WriteLine("Service Discovery ended with not success status: " + status);
    }
}

Here I always get the output: Characteristic is readable: False Permissions: 0 Later on gatt.ReadCharacteristic() returns false, which according to the sources of android is because I do not have the permissions to read. (see in the referenced question )

Answer 1

原来，甚至以为我不允许从特征读取值，而无需调用readCharacteristics()即可自动更新值，而我只需调用getValue() 。