ISSUE: DeviceAdvertised event on Android

[Auto72]

ISSUE: DeviceAdvertised event on Android

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[axa88]

I wonder if the DeviceAdvertised event is effected by the Adapter.ScanMatchMode. I wouldn't think so but you might try setting Adapter.ScanMatchMode = STICKY and see if that avoids your device from processing duplicate packets from the same device as it does during a Scan.

Otherwise you might try setting Adapter.ScanMode = Passive, but i really doubt that is going to have any impact on the DeviceAdvertised event either.

That said i don't believe DeviceAdvertised is called back on the UI thread, so you might look at other ways you might be tying up the UI thread unwittingly, but honestly I'm not confident in any of the advice im giving you here will help so...

[Auto72]

Thanks for your tips, I will try them and report here the result.

NOTE: On Android and iOS I found the MainThread.IsMainThread = true inside the event DeviceAdvertised, but not on Windows. I tried this.

private void Adapter_DeviceAdvertised(object? sender, Plugin.BLE.Abstractions.EventArgs.DeviceEventArgs e)
{
    Debub.WriteLine($"IsMainThread: {MainThread.IsMainThread}");    // returns True on Android and iOS, but not on Windows.
}

[Auto72]

I used to set Adapter.ScanMode = ScanMode.LowLatency in Xamarin with no problem.
In .NET MAUI I have the issue reported above on Android.
Adapter.ScanMatchMode is and has been always STICKY.
Using Adapter.ScanMode = ScanMode.Balanced is better, but sometimes the behaviour is similar to ScanMode.LowLatency
With Adapter.ScanMode = Passive I don't receive any scan device.

[axa88]

e is and has been always STICKY.
Using Adapter.ScanMode = ScanMode.Balanced is better, but sometimes the behaviour is similar to ScanMode.LowLatency
With Adapter.ScanMode = Passive I don't receive any scan device.

Unsure. im able to get good response both on windows and Android
Perhaps post a gist and someone might be able to comment...

[janusw]

Are you saying that the DeviceAdvertised event on Android is only raised on the main thread in MAUI, but not in Xamarin? Or are you just saying that the performance is worse with MAUI?

[janusw]

How to handle this situation probably depends a bit on your kind of setup and what you're trying to achieve.

First question: Are all of these advertisements even relevant for you? If not, you should probably use a scan filter to reduce the number of advertisements you have to process.

Then, of course, you should do as little work as possible in response to an advertisement (but you're probably already doing that, I hope).

And finally you can try to do the processing in the background, e.g. via a ThreadPool (which re-uses the threads in the pool and avoids the overhead of creating a new thread for each task).

AFAICS the library does nothing specific to put these events on the main thread, but just passes them on as they come from the OS.

[Auto72]

Are you saying that the DeviceAdvertised event on Android is only raised on the main thread in MAUI, but not in Xamarin? Or are you just saying that the performance is worse with MAUI?

No, I'm saying that in Xamarin as in .NET MAUI the DeviceAdvertised event is raised on the main thread.
While in Xamarin the event is raised 9 times per seconds, in .NET MAUI it is raised 106 times per seconds.
I tested the same environment with Xamarin App and .NET MAUI App.
In Xamarin the advertisements are only for my device, in .NET MAUI from all kind of devices.
The advertising interval for my BLE device is 2 or 3 times per second.

[Auto72]

How to handle this situation probably depends a bit on your kind of setup and what you're trying to achieve.

First question: Are all of these advertisements even relevant for you? If not, you should probably use a scan filter to reduce the number of advertisements you have to process.

Then, of course, you should do as little work as possible in response to an advertisement (but you're probably already doing that, I hope).

And finally you can try to do the processing in the background, e.g. via a ThreadPool (which re-uses the threads in the pool and avoids the overhead of creating a new thread for each task).

AFAICS the library does nothing specific to put these events on the main thread, but just passes them on as they come from the OS.

First answer:
No, I'm interested only in my devices, that have the name that start with a prefix.
I see how to put a filter, but it seems I can't specify a mask, like "Prefix*".
https://github.com/dotnet-bluetooth-le/dotnet-bluetooth-le#scan-filtering

I use the DeviceAdvertised event for two reasons:
a) I get the device before the event DeviceDiscovered is raised, so I can show it soon.
b) I get the value of RSSI updated.

Sure, I tried with Task.Run() but it doesn't work.
I think the library put all the advertisements in a queue and raise the event until the queue is empty, even if the scan has been stopped.

[Auto72]

I reviewed my code and now I used Task.Run() also in the DeviceDiscovered event and other adjustments.
I set Adapter.ScanMode = Balanced for Android.
Now seems a little bit better, but anyway it raises 90 events per minute.

I solved setting a filter by ServiceUuids.

var scanFilterOptions = new ScanFilterOptions { ServiceUuids = [Guid.Parse(MyStringGUID)] };
adapter.StartScanningForDevicesAsync(scanFilterOptions);

Thanks.