Question

i have a problem as subject said.

i have a Table courses in sql server Fields are courseID and course.

what i want is list the course in dopdown and i succeeeded but what i’m not able to do is when i select a course from dropdown list, a courseID should be selected in HiddenField/textbox/label

how to do that

here is a code i tried::

protected void Page_Load(object sender, EventArgs e)
{
    string select = "select * from courses";
    DropDownList1.Items.Add("-- Select Course --");
    DropDownList1.SelectedIndex = 0;
    DataTable dt = con.select_command(select);
    for (int i = 0; i < dt.Rows.Count; i++)
    {
        DropDownList1.Items.Add(dt.Rows[i][1].ToString());
        DropDownList1.DataValueField = dt.Rows[i][0].ToString();
        DropDownList1.DataTextField = dt.Rows[i][1].ToString();
    }        

}

in dropdownlist i’m getting values in Page Load method

i also tried dropdownlist_selectedindex change method too to select courseID

protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
{
    LLabel1.Text = DropDownList1.SelectedValue.ToString();
}

what i’m doing wrong ???

Answer 1

Place a block of if (!IsPostBack) before you update the dropdown in your page_load
The problem is that your code will re-populate the dropdown menu after the DropDownList1_SelectedIndexChanged event will be triggred.

That will make a post request to the server and he will run the DropDownList1_SelectedIndexChanged function attached to the IndexChange event and then page_load

because the page suppose to be loaded again
and will result in a new selected value that will not be what you expect it to be.

One more thing: use string identifiers when getting a value from a Row of a DataTable the code will be much more friendly that way. (Readability is very important…)

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
    string select = "select * from courses";
    DropDownList1.Items.Add("-- Select Course --");
    DropDownList1.SelectedIndex = 0;
    DataTable dt = con.select_command(select);
    for (int i = 0; i < dt.Rows.Count; i++)
    {
        DropDownList1.Items.Add(dt.Rows[i]["CourseName"].ToString());
        DropDownList1.DataValueField = dt.Rows[i]["CourseID"].ToString();
        DropDownList1.DataTextField = dt.Rows[i]["CourseName"].ToString();
    }
    }        

}