public class ViewModel : INotifyPropertyChanged
    {
       
        SqlConnection con;
        SqlCommand cmd;
        SqlDataAdapter adapter;
        DataSet ds;
       
        public static ObservableCollection<Model> Items { get; set; } = new ObservableCollection<Model>()
        {
              new Model(){ Name="Table2020" ,  ConStr=@"constr1"},
              new Model(){ Name="Table2021", ConStr= @"constr1"},
              new Model(){ Name="Table2022", ConStr= @"constr1"},
        };
        private string selectedItem = Items.FirstOrDefault().ConStr; 
        public string SelectedItem
        {
            get { return selectedItem; }
            set
            {
                if (selectedItem != value)
                {
                    selectedItem = value;
                    OnPropertyChanged("SelectedItem");
                    Changed();
                }
            }
        }
        public void Changed()
        {
            Bills.Clear();
            Bills = GetDatas();
            BillsView = CollectionViewSource.GetDefaultView(Bills);
        }
        private ICollectionView billsView;
        public ICollectionView BillsView
        {
            get { return billsView; }
            set
            {
                billsView = value;
                OnPropertyChanged("BillsView");
            }
        }
        private ObservableCollection<Bill> bills;
        public ObservableCollection<Bill> Bills
        {
            get { return bills; }
            set
            {
                bills = value;
                OnPropertyChanged("Bills");
            }
        }
        public  ObservableCollection<Bill> GetDatas()
        {
                con = new SqlConnection(SelectedItem);
                con.Open();
                cmd = new SqlCommand("select * from [dbo].[BillData]", con);
                adapter = new SqlDataAdapter(cmd);
                ds = new DataSet();
                adapter.Fill(ds, "[dbo].[BillData]");
                var Bills = new ObservableCollection<Bill>();

                foreach (DataRow dr in ds.Tables[0].Rows)
                {
                    Bills.Add(new Bill
                    {
                        Id = Convert.ToInt32(dr[0].ToString()),
                        Party = dr[1].ToString(),
                    });
                }
            
            con.Close();
            return Bills;

        }
        public ViewModel()
        {
            Bills =GetDatas();
            BillsView = CollectionViewSource.GetDefaultView(Bills);
        }
        public event PropertyChangedEventHandler PropertyChanged;
        protected void OnPropertyChanged([CallerMemberName] string name = null)
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(name));
        }
    }
    public class Bill
    {
        public int Id { get; set; }
        public string Party { get; set; }
    }
   
    public class Model : INotifyPropertyChanged
    {
        private string name;
        public string Name
        {
            get { return name; }
            set
            {
                if (name != value)
                {
                    name = value;
                    OnPropertyChanged("Name");
                }
            }
        }
        private string conStr;
        public string ConStr
        {
            get { return conStr; }
            set
            {
                if (conStr != value)
                {
                    conStr = value;
                    OnPropertyChanged("ConStr");
                }
            }
        }
        public  Model(){}
        public  Model(string constr){}

        public event PropertyChangedEventHandler PropertyChanged;
        protected void OnPropertyChanged([CallerMemberName] string name = null)
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(name));
        }
    }