you can try to convert java code into c#, for example:

[BroadcastReceiver(Enabled = true)]
[IntentFilter(new[] { Android.Content.Intent.ActionHeadsetPlug })]
public class MyBroadcastReceiver : BroadcastReceiver
{

    bool Microphone_Plugged_in = false;
    public override void OnReceive(Context context, Intent intent)
    {
        String action = intent.Action;
        int iii;
        if (Intent.ActionHeadsetPlug.Equals(action))
        {
            iii = intent.GetIntExtra("state", -1);
            if (iii == 0)
            {
                Microphone_Plugged_in = false;
                Toast.MakeText(context, "microphone not plugged in", ToastLength.Long).Show();
            }
            if (iii == 1)
            {
                Microphone_Plugged_in = true;
                Toast.MakeText(context, "microphone plugged in", ToastLength.Long).Show();
            }
        }
    }
}

And usage:

BroadcastReceiver broadcastReceiver;
IntentFilter receiverFilter;

and initialize value in method OnCreate of your activity:

broadcastReceiver = new MyBroadcastReceiver();
receiverFilter = new IntentFilter(Intent.ActionHeadsetPlug);

And RegisterReceiver and UnregisterReceiver by override method OnResume and OnPause

    protected override void OnResume()
    {
        base.OnResume();
        RegisterReceiver(broadcastReceiver, receiverFilter);
    }

    protected override void OnResume()
    {
        base.OnResume();

        IntentFilter receiverFilter = new IntentFilter(Intent.ActionHeadsetPlug);
        RegisterReceiver(broadcastReceiver, receiverFilter);
    }

For more, you can check thread: Detecting whether a headset is plugged into an Android device or not.

https://learn.microsoft.com/en-us/xamarin/android/app-fundamentals/broadcast-receivers

You have to write the code in xamarin.android file. Use broadcast receiver for implementation. In onReceive() you will get the intent as Intent.ACTION_HEADSET_PLUG.

Following pseudo code might help you,

public class MainActivity extends AppCompatActivity {
   BroadcastReceiver broadcastReceiver;
   boolean Microphone_Plugged_in = false;
   @Override
   protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
      broadcastReceiver = new BroadcastReceiver() {
         @Override
         public void onReceive(Context context, Intent intent) {
            final String action = intent.getAction();
            int iii;
            if (Intent.ACTION_HEADSET_PLUG.equals(action)) {
               iii = intent.getIntExtra("state", -1);
               if (iii == 0) {
                  Microphone_Plugged_in = false;
                  Toast.makeText(getApplicationContext(), "microphone not plugged in", Toast.LENGTH_LONG).show();
               }
               if (iii == 1) {
                  Microphone_Plugged_in = true;
                  Toast.makeText(getApplicationContext(), "microphone plugged in",
                  Toast.LENGTH_LONG).show();
               }
            }
         }
      };
      IntentFilter receiverFilter = new IntentFilter(Intent.ACTION_HEADSET_PLUG);
      registerReceiver(broadcastReceiver, receiverFilter);
   }
}

[BroadcastReceiver(Enabled = true)]
[IntentFilter(new[] { Android.Content.Intent.ActionHeadsetPlug })]
public class HeadsetPlugBroadcastReceiver : BroadcastReceiver
{
    public override void OnReceive(Context context, Intent intent)
    {
        String action = intent.Action;
        if (Intent.ActionHeadsetPlug.Equals(action))
        {
            var state = intent.GetIntExtra("state", -1);
            if (state == 0)
            {
                // Plugged out
            }
            if (state == 1)
            {
                // Plugged in
            }
        }
    }
}

I’m trying to find a way to detect the plugged/unplugged event on headphone Jack in Xamarin.Android. Is there a way to do it in this? and if it is, how can I implement that functionality?