fix: android calling

Author: rajamatt

src/Uno.UWP/ApplicationModel/Calls/Internal/CallCallback.Android.cs

@@ -0,0 +1,16 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using Android.Runtime;
+using Android.Telephony;
+
+namespace Windows.ApplicationModel.Calls
+{
+	internal class CallCallback : TelephonyCallback, TelephonyCallback.ICallStateListener
+	{
+		public void OnCallStateChanged(int state)
+		{
+			PhoneCallManager.RaiseCallStateChanged();
+		}
+	}
+}

src/Uno.UWP/ApplicationModel/Calls/PhoneCallManager.Android.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Text;
+using System.Threading;
 using Android.Content;
 using Android.OS;
 using Android.Telephony;
@@ -20,11 +21,32 @@ static PhoneCallManager()
 					"PhoneCallManager was used too early in the application lifetime. " +
 					"Android app context needs to be available.");
 			}
+
 			_telephonyManager = (TelephonyManager)ContextHelper.Current
 				.GetSystemService(Context.TelephonyService);
+
+#pragma warning disable CS0618 // TelephonyManager is obsolete in API 31
+#pragma warning disable CA1422 // Validate platform compatibility
+			if (Build.VERSION.SdkInt < BuildVersionCodes.S)
+			{
+				_telephonyManager.Listen(new CallStateListener(), PhoneStateListenerFlags.CallState);
+			}
+			else
+			{
+				RegisterTelephonyCallbackAsync();
+			}
+#pragma warning restore CA1422 // Validate platform compatibility
+#pragma warning restore CS0618 // TelephonyManager is obsolete in API 31
+		}
+
+		private static async void RegisterTelephonyCallbackAsync()
+		{
 #pragma warning disable CS0618 // TelephonyManager is obsolete in API 31
 #pragma warning disable CA1422 // Validate platform compatibility
-			_telephonyManager.Listen(new CallStateListener(), PhoneStateListenerFlags.CallState);
+			if (await Extensions.PermissionsHelper.TryGetPermission(CancellationToken.None, Android.Manifest.Permission.ReadPhoneState))
+			{
+				_telephonyManager.RegisterTelephonyCallback(ContextHelper.Current.MainExecutor, new CallCallback());
+			}
 #pragma warning restore CA1422 // Validate platform compatibility
 #pragma warning restore CS0618 // TelephonyManager is obsolete in API 31
 		}