将项目插入下拉列表

Question

I want to display the items in my dropdownlist2 (from table 2 )based on the selected item of the dropdownlist1(from table 1) .

in the following, i just tried to select the lang column values from table2 based on the value which is in the dropdownlist1..((just to insert into the dropdownlist1)) is that correct code...?

    SqlDataAdapter da = new SqlDataAdapter(
       "Select lang from table2 whereheatre=@d",connect.con());
    da.SelectCommand.Parameters.AddWithValue("@d", DropDownList1.SelectedItem.Text);
    DataSet ds=new DataSet();
    da.Fill(ds,"l1");
    DropDownList2.Items.Add(ds);

is there any other way to do that...?

Answer 1

To add the new values into an existing dropdownlist, you should add the new rows manualy :

foreach (DataRow dr in ds.Tables[0].Rows)
{
    DropDownList2.Items.Add(new ListItem(dr["TextField"].ToString(), dr["ValueField"].ToString()));
}

Or, you should merge datatables before binding them to your dropdownlist.

Answer 2

If you only want DropDownList2 to be populated with the values that are returned after the query you just mentioned you should just Databind it.

SqlDataAdapter da = new SqlDataAdapter(
   "Select lang from table2 whereheatre=@d",connect.con());
da.SelectCommand.Parameters.AddWithValue("@d", DropDownList1.SelectedItem.Text);
DataSet ds=new DataSet();

DropDownList2.DataSource = ds;
DropDownList2.DataTextField = "lang";
DataBind();

Whats more, you can also add a value field to the dropdown list this way(but you must modify the sql query so it wold return 2 columns):

"Select lang,colId from table2 whereheatre=@d"

DropDownList2.DataSource = ds;
DropDownList2.DataTextField = "lang";
DropDownList2.DataValueField= "colId ";
DataBind();

Good luck! ;)

Answer 3

Try wiring up the SelectedIndexChanged event on dropdownlist one and then bind dropdownlist two. I am assuming you are using Asp.net...

This would be in your aspx page:

<asp:DropDownList ID="ddlOne"runat="server" OnSelectedIndexChanged="ddlOne_OnSelectedIndexChanged"
                                AutoPostBack="true" />

<asp:DropDownList ID="ddlTwo"runat="server" DataTextField="lang" DataValueField="colId"  />

This would be in your codebehind:

protected void ddlOne_OnSelectedIndexChanged(object sender, EventArgs e)
 {
       // Go get your data here then bind to it..
       ddlTwo.DataSource = "Whatever datasource you want here";
       ddlTwo.DataBind();
 }