Database 如何将在VisualStudio中创建的SQLite数据库与表单的代码连接起来？

输出表明，

dkw未找到任何连接

以下代码段分别用于类
数据库
和表单的代码：



public class DataBase
{
    SQLiteConnection cnx;

    // Creates an empty database file
    public void createNewDatabase()
    {
        SQLiteConnection.CreateFile("MyDatabase.sqlite");
    }

    // Creates a connection with our database file.
    public SQLiteConnection connectToDatabase()
    {
        cnx = new SQLiteConnection("Data Source=MyDatabase.sqlite;Version=3;");
        cnx.Open();
        return cnx;
    }
    public void Close()
    {
        cnx.Close();
    }
    public void createTable()
    {
        
        string sql = "create table Users (username varchar(50), password varchar(15)";
        SQLiteCommand command = new SQLiteCommand(sql,cnx);
        command.ExecuteNonQuery();
    }
}

public partial class UserLogin : Form
{
    DataBase db = new DataBase();
    SQLiteConnection cnx;
    private void Form1_Load(object sender, EventArgs e)
    {
        db.createNewDatabase();
        cnx = new SQLiteConnection(db.connectToDatabase());
        db.createTable();
    }
    public UserLogin()
    {
        InitializeComponent();
        textBox2.PasswordChar = '*';
        textBox2.MaxLength = 15;
    }

    private void exit_button_Click(object sender, EventArgs e)
    {
        this.Hide();
        Application.Exit();
    }
   
    private void register_button_Click(object sender, EventArgs e)
    {
        try
        {
            //Inserta un nuevo usuario en la base de datos
            Console.WriteLine("Base de datos abierta");
            string username = textBox1.Text;
            string password = textBox2.Text;
            string query = "Insert into Users (username , password) values ('" + username + "','" + password + "')";
            SQLiteCommand command = new SQLiteCommand(query, cnx);
            int resultado = command.ExecuteNonQuery();
            if (resultado == 1)
            {
                MessageBox.Show("Insercion realizada");
            }
            else
            {
                MessageBox.Show("Error inserción");

            }
            //Cierra conexión con la base de datos
            cnx.Close();
        }

        catch (Exception o)
        {
            MessageBox.Show("error" + o.Message);
        }

        textBox1.Text = "";
        textBox2.Text = "";
    }

    private void login_button_Click(object sender, EventArgs e)
    {
        string username = textBox1.Text;
        string password = textBox2.Text;
        bool authentication = false;

        try
        {
            //En este objeto (resultado tabla) va a ir a parar toda la informacion extraida
            DataTable res = new DataTable();
            if (username != "" && password != "")
            {
                SQLiteDataAdapter adp = new SQLiteDataAdapter ("SELECT Username,Password FROM Users WHERE (Username = '" + username + "' and Password = '" + password + "')", cnx);
                // Si encuentra el usuario en la base de datos rows valdrá 1
                int rows = adp.Fill(res);


                if (rows == 1)
                {
                    authentication = true;
                }
            }
            cnx.Close();
        }
        catch (Exception o)
        {
            MessageBox.Show("error" + o.Message);
        }

        // Si el usuario existe y la contraseña es correcta crea un nuevo formulario principal y lo muestra en pantalla
        if (authentication)
        {
            Principal form = new Principal();
            form.Show();
            this.Hide();

        }

        else
        {
            MessageBox.Show("The user doesn't exist or de data isn't well introduced");
        }
    }
}