Difficulty in listing SQLite result in ListView Android

I'm creating an application to train mobile development, I'm doing for Android in Visual Studio, using Xamarin. I'm having trouble listing an SQLite result.

I created two activities, one to do the registration and already list, and the other just to list the data registered in a ListView. The problem is, in the first activity, when inserting a data, it lists the others (that already exist in the database) normally, but in the second activity, when loading the app, it throws an exception: "Unhandled Exception: System.NullReferenceException: Object reference not set to an instance of an object occurred." The exception is in the following code snippet:

lista.Adapter = adapter; 

Follow the codes:

Function that brings results:

public List<Abastece> GetAbastecimentos()
    {
        try
        {
            using (var conexao = new SQLiteConnection(System.IO.Path.Combine(pasta, "Abastece.db")))
            {
                return conexao.Table<Abastece>().ToList();
            }
        }
        catch (SQLiteException ex)
        {
            Log.Info("SQLiteEx", ex.Message);
            return null;
        }
    } 

C # code:

namespace Control_Car
{
[Activity(Label = "ListaAbast", MainLauncher = true)]
public class ListaAbast : Activity
{
    Button button;
    ListView lista;
    DataBase db;
    protected override void OnCreate(Bundle savedInstanceState)
    {
        CriarBancoDeDados();
        base.OnCreate(savedInstanceState);

        button = (Button)FindViewById(Resource.Id.bt_registrar);
        lista = (ListView)FindViewById(Resource.Id.lista);
        SetContentView(Resource.Layout.ListaAbast);

        var listaAbast = db.GetAbastecimentos();
        ArrayAdapter adapter = new ArrayAdapter<Abastece>(this, 
        Android.Resource.Layout.SimpleListItemMultipleChoice, listaAbast);
        lista.Adapter = adapter;
        lista.Activated = true;
    }

    private void CriarBancoDeDados()
    {
        db = new DataBase();
        db.CriarBanco();
    }
}
}

Just reinforcing, this code in C # is in the two activity, however if I try to call the function of populating the ListView in OnCreate it throws the exception. For example I will put the code of the other activity, in which I want to only list the data when inserting some other:

namespace Control_Car
{
[Activity(Label = "Abastecer", ScreenOrientation = 
ScreenOrientation.Portrait)]
public class Abastecer : Activity
{
    Button btn;
    EditText valorKM, preco, litros, nomePosto;
    ListView ltAbastecimento;
    DataBase db;
    string[] items = { };
    List<Abastece> listaAbast = new List<Abastece>();

    protected override void OnCreate(Bundle savedInstanceState)
    {
        CriarBancoDeDados();


        base.OnCreate(savedInstanceState);
        SetContentView(Resource.Layout.Abastecer);

        btn = (Button)FindViewById(Resource.Id.bt_registrar);
        valorKM = (EditText)FindViewById(Resource.Id.valor_km);
        preco = (EditText)FindViewById(Resource.Id.valor_preco);
        litros = (EditText)FindViewById(Resource.Id.valor_litros);
        nomePosto = (EditText)FindViewById(Resource.Id.nome_posto);
        ltAbastecimento = (ListView)FindViewById(Resource.Id.lista);
        CarregaDados();

        btn.Click += delegate
        {
            Abastece abastece = new Abastece()
            {
                ValorKM = Double.Parse(valorKM.Text),
                Preco = Double.Parse(preco.Text),
                Litros_qnt = Double.Parse(litros.Text),
                PostoUt = nomePosto.Text
            };
            db.InserirAbastecimento(abastece);
            CarregaDados();
        };
    }

    private void CarregaDados()
    {
        listaAbast = db.GetAbastecimentos();
        ArrayAdapter<Abastece> adapter = new ArrayAdapter<Abastece>(this, 
    Android.Resource.Layout.SimpleListItem1, listaAbast);
        ltAbastecimento.Adapter = adapter;
    }

    private void CriarBancoDeDados()
    {
        db = new DataBase();
        db.CriarBanco();
    }
}
}