C# 登录表单错误“Position 0 处没有行”

Question

I am new to C# coding. When I enter the Username and Password in a Login Form application with values already stored in SignUp database, An Error There is no row at position 0" comes up.

Below is the link to error screenshot.

Screenshot: Error Message

And below is the code which is giving trouble.

private void button1_Click(object sender, EventArgs e)
{
    if (textBox1.Text == "" || textBox2.Text == "")
    {
        MessageBox.Show("!!Please fill in both Username and Password!! ");
    }
    else
    {
        SqlConnection sqlcon = new SqlConnection(@"Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=""C:\Users\Lenovo\Desktop\dev\C# .net\Aadi Paw Plethysmometer\Aadi Paw Plethysmometer\Database1.mdf"";Integrated Security=True");
        string query = "Select * from Signup where Username = '" + Username.Text.Trim() + "' and Password = '" + Password.Text.Trim() + "'";
        SqlDataAdapter sda = new SqlDataAdapter(query, sqlcon);
        DataTable dtbl = new DataTable();
        sda.Fill(dtbl);
        if (dtbl.Rows[0][0].ToString() == "1")
        {
            this.Hide();
            new Form2().Show();
        }
        else
        {
            MessageBox.Show("Invalid username or password");
            textBox1.Text = textBox2.Text = "";
        }
    }
}

And below is the link to screenshot of the SignUp Data Table.

Screenshot: SignUp Data Table

Answer 1

When no results are found in the DB, you are still trying to access Row 0 of the DataTable, which does not exist as your error states. Replace your condition as follows.:

 if (dtbl.Rows.Count > 0)