1> JAVAC: warning: unknown enum constant Scope.LIBRARY_GROUP in xamarin.android after adding xamari.support.v4 and xamarin.support.v7.AppC

during splash training Screen I add the package xamarin.support.v4 and xamarin.android.v7.appcompat each thin fine, I just get warning 1> JAVAC: warning: unknown enum constant Scope.LIBRARY_GROUP and my code works well: mine splash activity code:

enter code here
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using Android.App;
using Android.Content;
using Android.OS;
using Android.Runtime;
using Android.Views;
using Android.Widget;
using Android.Support.V7.App;
using System.Threading.Tasks;
using Android.Util;
namespace againCardview
{
[Activity(Label = "SplashActivity",MainLauncher =true,NoHistory                   =true,Theme = "@style/MyTheme.Splash")]
public class SplashActivity :AppCompatActivity
{
    string tag = "TAg" + typeof(SplashActivity).Name;
    public override void OnCreate(Bundle      savedInstanceState,PersistableBundle persist)
    {
        base.OnCreate(savedInstanceState,persist);
        Log.Debug(tag, "this is Oncreate method of splashActivity");
    }
    protected override void OnResume()
    {
        base.OnResume();
        var setartActivity = new Task(()=> {
            Log.Debug(tag, "Now App is starting");
            Task.Delay(50000);
            Log.Debug(tag, "now performing importing work");
        });
        setartActivity.ContinueWith(p => {
            Log.Debug(tag, "Starting App");
            StartActivity(new Intent(Application.Context,      typeof(MainActivity)));
        },TaskScheduler.FromCurrentSynchronizationContext());

    }
}

      

        
        
        
      

    

}