private async void loginbtn_Click(object sender, RoutedEventArgs e)
        {
            (App.Current as App).NavigateText = unametxt.Text;

            var path = ApplicationData.Current.LocalFolder.Path + "/myDb1.DB";
            var con = new SQLiteAsyncConnection(path);
            person p1 = new person();
            List<person> allpersons = new List<person>();
        
           allpersons = await con.QueryAsync<person>("select name,password from person where name=" + "\'" + unametxt.Text + "\'" + "and password="******"\'" + pwdtxt.Password + "\'");
           if (allpersons.Count == 1)
           {

               p1 = allpersons[0];
               Frame.Navigate(typeof(MainPage));
               
           }
        }