Filling a dropdown list, based on a selection from another dropdown list

This seemed like a simple venture, and may be, but with my limited asp.net knowledge, I am having a problem...  

Basically, I have a page that is gathering information. I want a user to be able to select a value from a dropdown list... On Auto postback I would like to make a second listbox visible and bind data to it based on the selection from the first. (While keeping the value of the first listbox available)
Right now I am filling my dataset with the tables used in the page load event and setting my second listbox.visible to false. in the SelectedIndex_change event of the first list box, I am setting the SelectCommand.commandtext property to a SQL string that includes the value of the first listbox in the where clause. (I have a data adapter for each dropdown, both attached to the same dataset)
If I databind() again, I lose the data in my first dropdown list (It comes back empty)... If I don't databind again, I get no data in my second list...
I know there is a "Right" way to do this :) and I hope someone out there can point me in the right direction... Thanks in advance!
0
rvitatoe
8/26/2004 2:44:43 PM
asp.net.presentation-controls 72751 articles. 3 followers. Follow

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I usually use datareaders rather than dataadapters for ddl.  See the code below.  I think maybe the problem you are having is that the first ddl is refreshing on postback and so you loose the selected index.  I use the 

if(!Page.IsPostBack){}

around my binding of the ddl to prevent this. Make sure to set AutoPostBack to true on both ddl.
GL
-Sam
Working code below!!!

public class ddl_test : System.Web.UI.Page
{
protected System.Web.UI.WebControls.DropDownList ddl_list1;
protected System.Web.UI.WebControls.DropDownList ddl_list2;
protected System.Data.SqlClient.SqlConnection conn_sql;
protected System.Data.SqlClient.SqlCommand cmd_sql;
protected System.Data.SqlClient.SqlCommand cmd_sql2;
protected System.Data.SqlClient.SqlDataReader dr_sql;
protected System.Data.SqlClient.SqlDataReader dr_sql2;

private void Page_Load(object sender, System.EventArgs e)
{
ddl_list2.Visible=true;
string connstring=ConfigurationSettings.AppSettings["cs_inmotion10"].ToString();
string commstring="SELECT * FROM dbo.docs;";

conn_sql=new SqlConnection(connstring);
cmd_sql=new SqlCommand(commstring,conn_sql);
if(!Page.IsPostBack)
{
conn_sql.Open();
dr_sql=cmd_sql.ExecuteReader();
ddl_list1.DataSource=dr_sql;
ddl_list1.DataTextField="lastname";
ddl_list1.DataValueField="lastname";
ddl_list1.DataBind();
conn_sql.Close();
}
}
#region Web Form Designer generated code
override protected void OnInit(EventArgs e)
{
//
// CODEGEN: This call is required by the ASP.NET Web Form Designer.
//
InitializeComponent();
base.OnInit(e);
}

/// <summary>
/// Required method for Designer support - do not modify
/// the contents of this method with the code editor.
/// </summary>
private void InitializeComponent()
{
this.ddl_list1.SelectedIndexChanged += new System.EventHandler(this.ddl_list1_SelectedIndexChanged);
this.Load += new System.EventHandler(this.Page_Load);
}
#endregion
private void ddl_list1_SelectedIndexChanged(object sender, System.EventArgs e)
{
ddl_list2.Visible=true;
string selectionval=ddl_list1.SelectedItem.Value.ToString();
string commstring2="SELECT * FROM dbo.docs WHERE lastname='" + selectionval + "';";

cmd_sql2=new SqlCommand(commstring2,conn_sql);
conn_sql.Open();
dr_sql2=cmd_sql2.ExecuteReader();
ddl_list2.DataSource=dr_sql2;
ddl_list2.DataTextField="docid";
ddl_list2.DataValueField="docid";
ddl_list2.DataBind();
conn_sql.Close();
}
}
0
froman21
8/27/2004 2:34:15 AM
Reply:

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