How can I insert data into login form?

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C#

SQL-Server

Visual-Studio

Hello! So i have a Login Form and i have to insert Login and Password through SqlDataAdapter, but i don't know how to do it using TextBox of Login And Password, and i get the next error:

System.Data.SqlClient.SqlException: "The parameterized query '(@DocName nvarchar(50),@DocPass nvarchar(50))SELECT * FROM Docto' expects the parameter '@DocName', which was not supplied."

What I have tried:

Code of the form: 
<pre>public static SqlDataAdapter CreateCustomerAdapter(SqlConnection conn)
        {
            SqlDataAdapter adapter = new SqlDataAdapter();

            // Create the SelectCommand.
            SqlCommand command = new SqlCommand("SELECT * FROM Doctor " +
                "WHERE DocName = @DocName AND DocPass = @DocPass", conn);

            // Add the parameters for the SelectCommand.
            command.Parameters.Add("@DocName", SqlDbType.NVarChar, 50);
            command.Parameters.Add("@DocPass", SqlDbType.NVarChar, 50);

            adapter.SelectCommand = command;

            return adapter;
        }


        private void button1_Click(object sender, EventArgs e)

        {
            conn.Open();
            SqlDataAdapter sda = CreateCustomerAdapter(conn);
            DataTable dt = new DataTable();
            sda.Fill(dt);
            if (dt.Rows[0][0].ToString() == "1")
            {
                Home H = new Home();
                H.Show();
                this.Hide();
            }
            else
            {
                MessageBox.Show("Invalid login or password");
            }
            conn.Close();
        }

I think in the next lines

<pre>command.Parameters.Add("@DocName", SqlDbType.NVarChar, 50);
            command.Parameters.Add("@DocPass", SqlDbType.NVarChar, 50);

i should replace

SqlDbType.NVarChar, 50

with Textboxes DocName.Text and DocPassword.Text, but it doesn't seem to work.