GetPrimaryServiceAsync not working on Android 16

[vitalii-vov]

When I updated my device to Android 16, GetPrimaryServiceAsync stopped returning a value and is always awaiting.

var service = await device.Gatt.GetPrimaryServiceAsync(BluetoothUuid.FromGuid(serviceUuid));

I don't see any errors in the logs or Logcat.

[peterfoot]

On Android we call FetchUuidsWithSdp. If this fails and returns false we might see this behaviour because we are still waiting on the receiver to get the Uuids. I'm adding a fix for this now. As for why it might fail, the documentation doesn't give any clear scenarios, other than permissions - You must include BLUETOOTH_CONNECT on Android 12+ and also have prompted the user for permission prior to calling this.

[vitalii-vov]

BLUETOOTH_CONNECT requested.
The problem only occurs on Android 16.

    <uses-feature android:name="android.permission.BLUETOOTH_LE" android:required="false"/>
    <uses-permission android:name="android.permission.BLUETOOTH" android:maxSdkVersion="30"/>
    <uses-permission android:name="android.permission.BLUETOOTH_ADMIN" android:maxSdkVersion="30"/>
    <uses-permission android:name="android.permission.BLUETOOTH_CONNECT"/>
    <uses-permission android:name="android.permission.BLUETOOTH_SCAN" android:usesPermissionFlags="neverForLocation"/>
    <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" android:maxSdkVersion="30"/>
    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" android:maxSdkVersion="30"/>
    <uses-permission android:name="android.permission.POST_NOTIFICATIONS"/>
    <uses-permission android:name="android.permission.FOREGROUND_SERVICE"/>

[vitalii-vov]

After update project to .net9 and update library to 4.0.43
I get error when I try to connect to device after disconnecting.

What I do:

1. Connect to device

public async Task Connect(BluetoothDevice device)
{
    _device = device;
    await _device.Gatt.ConnectAsync();
}

2. Disconnect from device

public void Disconnect()
{
    _device.Gatt.Disconnect();
}

3. Try to connect to device again... App crush

[ERROR] FATAL UNHANDLED EXCEPTION: System.OperationCanceledException: The operation was canceled.
   at MyApp.Ble.Connection.Connect(BluetoothDevice device) in /MyApp/MyApp/Ble/Connection.cs:line 25
   at MyApp.UI.ViewModels.MainViewModel.<SelectDevice>b__66_0() in /MyApp/MyApp/UI/ViewModels/MainViewModel.cs:line 523
   at System.Threading.Tasks.Task.<>c.<ThrowAsync>b__128_0(Object state)
   at Android.App.SyncContext.<>c__DisplayClass2_0.<Post>b__0() in /Users/runner/work/1/s/xamarin-android/src/Mono.Android/Android.App/SyncContext.cs:line 36
   at Java.Lang.Thread.RunnableImplementor.Run() in /Users/runner/work/1/s/xamarin-android/src/Mono.Android/Java.Lang/Thread.cs:line 37
   at Java.Lang.IRunnableInvoker.n_Run(IntPtr jnienv, IntPtr native__this) in /Users/runner/work/1/s/xamarin-android/src/Mono.Android/obj/Release/net9.0/android-35/mcw/Java.Lang.IRunnable.cs:line 59
   at Android.Runtime.JNINativeWrapper.Wrap_JniMarshal_PP_V(_JniMarshal_PP_V callback, IntPtr jnienv, IntPtr klazz) in /Users/runner/work/1/s/xamarin-android/src/Mono.Android/Android.Runtime/JNINativeWrapper.g.cs:line 22
2025-11-08 17:38:22.908 14297-14307 BluetoothGatt           com.company.MyApp                    D  onSearchComplete(XX:XX:XX:XX:C8:57, _, 0)
2025-11-08 17:38:22.923 14297-14331 

[peterfoot]

The Android code uses disconnect() and not close() so it should allow the same gatt server to be reconnected. I'll need to try to recreate this on an Android 16 device

[jargule]

I also get this error, on a Samsung S24 Android 16, but when trying to connect for the first time. I am using FromIdAsync(GUID) to get the BluetoothDevice object, instead of pairing. The Samsung A51 Android 13 device works just fine this way. I am connecting to a Linux box that uses Bluez (typical for Linux) and it uses the Gobbledegook library as its Bluetooth server with a Bluetooth 4.2 USB. Now if I instead pair first, using a different app, and call PickSingleDeviceAsync() I do not get the error