在页面加载时填充列表框

Question

Im attempting to populate a listbox from a database on form load, but when i load the form no data appears. The connection to the database is setup in VS 2017 and thats where I got the connection string.

namespace listbox
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            fillListBox();
        }

        void fillListBox()
        {
            SqlConnection con = new SqlConnection();
            con.ConnectionString = "Data Source=computername\\SQLEXPRESS;Initial Catalog=footfall;Integrated Security=True";
            con.Open();
            SqlCommand cmd = new SqlCommand("select category from category",con);
            SqlDataReader reader = cmd.ExecuteReader();
            categoryBox.Items.Clear();
            while (reader.Read())
            {
                categoryBox.Items.Add(reader.ToString());
            }
            con.Close();
        }
    }
}

Answer 1

You don't want reader.ToString() (which returns the type name) but reader.GetString(0) :

while (reader.Read())
{
    categoryBox.Items.Add(reader.GetString(0));
}