Xamarin Forms BLE Plugin Scan Issue Android 12

Question

I have written a xamarin forms app which uses the Plugin.BLE NuGet package to scan and connect to ble devices. It was working/debugging flawlessly on my phone until it(my phone) updated to Android 12.0 - API 31. I am using the basic vanilla implementation from the plugin:

adapter.DeviceDiscovered += (s,a) => deviceList.Add(a.Device);
await adapter.StartScanningForDevicesAsync();

I have found that Android 12 requires different runtime permissions ([https://developer.android.com/guide/topics/connectivity/bluetooth/permissions#declare-android11-or-lower][1]) and I have tried to accomodate them in the manifest file:

    <uses-sdk android:minSdkVersion="21" android:targetSdkVersion="28" />
    <application android:label="Rep_001.Android" android:theme="@style/MainTheme"></application>
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
    <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
    <uses-permission android:name="android.permission.BLUETOOTH_PRIVILEGED" />
    <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_SCAN" />
    <uses-permission android:name="android.permission.BLUETOOTH_CONNECT" />
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
    <uses-feature android:name="android.hardware.bluetooth_le" android:required="true" />https://developer.android.com/guide/topics/connectivity/bluetooth/permissions#declare-android11-or-lower

but alas I am having no luck. I am thinking that I need to ask the user for scan and connect privileges at runtime but I am not sure how to do that as Xamarin.Essentials does not have bluetooth permissions requests.

Answer 1

Well, I figured it out. Within the Android Project, I created a class that inherits from Xamarin.Essentials.Permissions.BasePlatformPermission:

 public class BLEPermission : Xamarin.Essentials.Permissions.BasePlatformPermission
{
    public override (string androidPermission, bool isRuntime)[] RequiredPermissions => new List<(string androidPermission, bool isRuntime)>
{
    (Android.Manifest.Permission.BluetoothScan, true),
    (Android.Manifest.Permission.BluetoothConnect, true)
}.ToArray();
}

Then within MainActivity.cs -> OnCreate() I inserted the RequestAsync immediately after the Application is loaded:

        protected override async void OnCreate(Bundle savedInstanceState)
    {
        base.OnCreate(savedInstanceState);

        Xamarin.Essentials.Platform.Init(this, savedInstanceState);
        global::Xamarin.Forms.Forms.Init(this, savedInstanceState);
        LoadApplication(new App());

        await Permissions.RequestAsync<BLEPermission>();
    }

Now when the app loads for the first time it asks the user for bluetooth scanning an connecting permissions. All subsequent launches do not re-prompt for permissions. Sites/Documentation that helped along the way

https://developer.android.com/guide/topics/connectivity/bluetooth/permissions#declare-android11-or-lower

https://learn.microsoft.com/en-us/xamarin/android/app-fundamentals/permissions?tabs=windows

Answer 2

The BLUETOOTH_ADVERTISE, BLUETOOTH_CONNECT, and BLUETOOTH_SCAN permissions are runtime permissions.

Therefore, you must explicitly request user approval in your app before you can look for Bluetooth devices, make a device discoverable to other devices, or communicate with already-paired Bluetooth devices.

When your app requests at least one of these permissions, the system prompts the user to allow your app to access Nearby devices.