从数据库获取数据到ComboBox

Question

Short one.

A database named ComDet , and column cID(PK) , cName , cDet , mainCate(FK) , Subcat(FK).

this suppose to get the data from table ComDet to the combobox..

DataSet ds2;

private void searchBtn_Click(object sender, EventArgs e)
{
    SqlConnection conn = new SqlConnection();
    conn.ConnectionString = "Data Source=.\SQLEXPRESS;Initial Catalog=master;Integrated Security=True";
    conn.Open();

    SqlDataAdapter daSearch = new SqlDataAdapter("SELECT cName FROM ComDet", conn);
    ds2 = new DataSet();
    daSearch.Fill(ds2, "daSearch");
    ListU.ValueMember = "cName";
    ListU.DataSource = ds2.Tables["ComDet"];
    ListU.DropDownStyle = ComboBoxStyle.DropDownList;
    ListU.Enabled = true;
}

but it didnt work.. where did i go wrong? The Data(cName) from database table ComDet is not shown in the combobox. –

Answer 1

Problem : You are assigning database table name ComDet as DataSource but not DataTable Name daSearch to ComboBox .

Solution : you need to assign valid DataTable Name to ComboBox as Datasource .

Replace This :

ListU.DataSource = ds2.Tables["ComDet"];

With This:

ListU.DataSource = ds2.Tables["daSearch"];  

(or)

ListU.DataSource = ds2.Tables[0];

Complete Code:

DataSet ds2;

private void searchBtn_Click(object sender, EventArgs e)
{
SqlConnection conn = new SqlConnection();
conn.ConnectionString = "Data Source=.\SQLEXPRESS;Initial Catalog=master;Integrated Security=True";
conn.Open();

SqlDataAdapter daSearch = new SqlDataAdapter("SELECT cName FROM ComDet", conn);
ds2 = new DataSet();
daSearch.Fill(ds2, "daSearch");
ListU.ValueMember = "cName";
ListU.DataSource = ds2.Tables["daSearch"];
ListU.DropDownStyle = ComboBoxStyle.DropDownList;
ListU.Enabled = true;
}

Answer 2

So the question asks how to get data from database to combobox . Personally, I find using the DataSet class to be unpreferable - it is quite prone to errors like the asker is experiencing here.

Try this approach. Which reads all the cName into a List and binds the List to the ComboBox . Simple and readable code. The use of using statements also ensures that the unmanaged resources are released efficiently.

private void searchBtn_Click(object sender, EventArgs e)
{
    var list = new List<string>();
    using (var conn = new SqlConnection())
    {
        conn.ConnectionString = 
            "Data Source=.\SQLEXPRESS;Initial Catalog=master;Integrated Security=True";
        conn.Open();
        using (var cmd = new SqlCommand("SELECT cName FROM ComDet", conn))
        {
            using (var reader = cmd.ExecuteReader())
            {
                while (reader.Read())
                {
                    list.Add(Convert.ToString(reader["cName"]));
                }
            }
        }
   }
   ListU.DataSource = new BindingSource(list, null);
   ListU.DropDownStyle = ComboBoxStyle.DropDownList;
   ListU.Enabled = true;
}