How can I diagnose why BLE NotifyCharacteristic is not working?

[vchelaru]

I have the following code:

// Make sure the characteristic supports Notify
notifyCharacteristic.AssertNotify();
// Make sure the device is connected
System.Diagnostics.Debug.Assert(peripheral.IsConnected());
// Notify - is this all I have to do?
notifyCharacteristicResult = peripheral.NotifyCharacteristic(notifyCharacteristic);

int timesWaited = 0;
while(notifyCharacteristic.IsNotifying == false)
{
    // Check every second for the notify to be set to true...
    await Task.Delay(1_000);
    Console.WriteLine($"Waiting for notify to be true {timesWaited} seconds");
    timesWaited++;
    notifyCharacteristic = await peripheral
        .GetCharacteristicAsync(notifyCharacteristic.Service.Uuid, notifyCharacteristic.Uuid);
}

This produces the following output:

[0:] Attempting to notify
[monodroid-assembly] Shared library 'liblog' not loaded, p/invoke '__android_log_print' may fail
[DOTNET] Waiting for notify to be true 0 seconds
[DOTNET] Waiting for notify to be true 1 seconds
[etoothmauitest1] Explicit concurrent copying GC freed 47313(1743KB) AllocSpace objects, 0(0B) LOS objects, 83% free, 4743KB/28MB, paused 24us,18us total 12.264ms
[BluetoothAdapter] isLeEnabled(): ON
[DOTNET] Waiting for notify to be true 2 seconds
[DOTNET] Waiting for notify to be true 3 seconds
[DOTNET] Waiting for notify to be true 4 seconds
[DOTNET] Waiting for notify to be true 5 seconds
[DOTNET] Waiting for notify to be true 6 seconds
[DOTNET] Waiting for notify to be true 7 seconds
[DOTNET] Waiting for notify to be true 8 seconds
[DOTNET] Waiting for notify to be true 9 seconds
[DOTNET] Waiting for notify to be true 10 seconds
[DOTNET] Waiting for notify to be true 11 seconds
[DOTNET] Waiting for notify to be true 12 seconds
[DOTNET] Waiting for notify to be true 13 seconds

My expectation is that the code above would either result in notifyCharacteristic.IsNotifying being set to true, or some kind of output indicating that the notification, similar to:

Shiny.BluetoothLE.IPeripheral: Information: Subscribed to Notification Characteristic xxxx / xxx-xxx-xxx-xxx-xxxx

as shown here:

https://github.com/orgs/shinyorg/discussions/1277

Can anyone help me understand what I might be doing wrong?

[vchelaru]

For future readers, I believe the reason this wasn't working is because I wasn't subscribing to the NotifyCharacterstic response. The code should be:

peripheral.NotifyCharacteristic(notifyCharacteristic).Subscribe(HandleNotificationSubscription);
...
private void HandleNotificationSubscription(BleCharacteristicResult result)
{
    int m = 3;
}

Unfortunately I struggled with this longer than probably would have been necessary but the docs are incomplete here:
https://shinylib.net/client/ble/gatt/

But the following line provides clues:

Notifications will stay hooked as long as you hold a subscription to it. Make sure you dispose of it when you are done
I hope this helps future readers.

[aritchie]

Please don't complain about docs. This isn't a product. You are always welcome to contribute. Also note that library does say it is based on reactive extensions, so this is standard RX