public class BillsViewModel : ViewModelBase
    {
        private ICollectionView billsView;
        public ICollectionView BillsView
        {
            get { return billsView; }
            set
            {
                billsView = value;
                OnPropertyChanged("BillsView");
            }
        }
        private ObservableCollection<Bills> billss;
        public ObservableCollection<Bills> Billss
        {
            get { return billss; }
            set
            {
                billss = value;
                OnPropertyChanged("Billss");
            }
        }
  
        public static ObservableCollection<Model> Items { get; set; } = new ObservableCollection<Model>()
        {
              new Model(){ Name="Table2020" ,  ConStr="Data Source=test.db"},
              new Model(){ Name="Table2021", ConStr= "Data Source=test1.db"},

        };

        public  string selectedItem = Items.FirstOrDefault().ConStr;
        public  string Tab1SelectedItem
        {
            get { return selectedItem; }
            set
            {
                if (selectedItem != value)
                {
                    selectedItem = value;
                    OnPropertyChanged("Tab1SelectedItem");

                    BillsView.Refresh();
                    Changed();
                }
            }
        }
        public void Changed()
        {
            Billss.Clear();
            Billss = GetAllBillsFromDB();
            BillsView = CollectionViewSource.GetDefaultView(Billss);
        }
        public  ObservableCollection<Bills> GetAllBillsFromDB()
        {
            SQLiteConnection con = new SQLiteConnection(Tab1SelectedItem);
            con.Open();
            SQLiteCommand cmd = new SQLiteCommand("Select * From billdata", con);
            SQLiteDataAdapter adapter = new SQLiteDataAdapter(cmd);
            DataTable dt = new DataTable();
            adapter.Fill(dt);
            var Bills = new ObservableCollection<Bills>();
             foreach (DataRow dr in dt.Rows)
            {
                var p = (dr["PaidOn"] == DBNull.Value) ? String.Empty : (string)(dr["PaidOn"]);
                var q = (dr["Remarks"] == DBNull.Value) ? String.Empty : (string)(dr["Remarks"]);

                Bills.Add(new Bills
                {
                    Id = Convert.ToInt32(dr[0].ToString()),
                    Party = dr[1].ToString(),
                    BillNo = (string)dr["BillNo"],
                    BillDt = (string)(dr["BillDt"]),
                    Amt = (string)(dr["Amt"]),
                    DueDt = (string)(dr["DueDt"]),
                    PaidOn = p,
                    Remarks = q
                });
            }
            con.Close();
            return Bills;
        }
        public BillsViewModel()
        {
            Billss = GetAllBillsFromDB();
            BillsView = CollectionViewSource.GetDefaultView(Billss);
        }
    }