OK, this problem isn’t silverlight, but I did encounter it in my day job. In fact, I’ve encountered it several times, so I thought I would write it up so I can find it again.
The Problem: You write a web page that contains an updatable datagrid, which, when in EditMode, contains a dropdown list containing lookup items. The DropdownBox does not populate, and (later when you get it working) the proper listitem is not selected.
The Cause: Since the DropDownBox down not existing when the page loads, there is nothing to bind.
The Solution: You have to attach your events to some non-standard page events to get it to work. The relevant part of the .aspx page is below (put this in your datagrid)
<asp:TemplateColumn HeaderText=”Tactic Category”>
<HeaderStyle Font-Size=”Large” Font-Bold=”true” />
<ItemTemplate>
<%#DataBinder.Eval(Container.DataItem,”TacticCatName”)%>
</ItemTemplate>
<EditItemTemplate>
<%–Notice the GetCat() routine here as the datasource.–%>
<asp:DropDownList id=”ddTacticCatList” runat=”server” DataSource=”<%# GetCat() %>” DataTextField=”TacticCatName” DataValueField=”TacticCatID”>
</asp:DropDownList>
</EditItemTemplate>
</asp:TemplateColumn>
Your code-behind page should look like this (in C#)
private void MainCode()
{
string strID = Request.QueryString[“id”].ToString();
//custom code to get the relevant dataset for the entire datgrid
DataSet ds = LMR.TacticSubCatList(strID);
//custom code to bind to the datagrid
Utility.DGDSNullCheck(ds, dgTacticSubCatList, lblTacticSubCatList, “There are no tactic subcategories in the database at this time.”);
}
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
MainCode();
}
}
protected void dgTacticSubCatList_EditCommand(object source, System.Web.UI.WebControls.DataGridCommandEventArgs e)
{
//grab the index
dgTacticSubCatList.EditItemIndex = e.Item.ItemIndex;
MainCode();
}
protected void dgTacticSubCatList_UpdateCommand(object source, System.Web.UI.WebControls.DataGridCommandEventArgs e)
{
//get the id value of the selected datagrid item
int intTacticSubCatID = (int)dgTacticSubCatList.DataKeys[(int)e.Item.ItemIndex];
//this gets our textbox, also in the datagrid
TextBox EditText = null;
EditText=(TextBox)e.Item.FindControl(“tbTacticSubCatName”);
string strEditText = Convert.ToString(EditText.Text);
//get the value of our dropdown list
DropDownList dd = (DropDownList)e.Item.FindControl(“ddTacticCatList”);
string strTacticCatID = dd.SelectedValue.ToString();
//do our database update
LMR.TacticSubCatEdit(intTacticSubCatID.ToString(),strTacticCatID,strEditText);
//reset the datagrid
dgTacticSubCatList.EditItemIndex = -1;
//give feedback and rebind
lblFeedback.Text = “Your changes have been applied.”;
MainCode();
}
protected void dgTacticSubCatList_CancelCommand(object source, System.Web.UI.WebControls.DataGridCommandEventArgs e)
{
dgTacticSubCatList.EditItemIndex = -1;
MainCode();
}
protected DataTable GetCat()
{
//here is where we get the dataset to populate the dropdown list – it does have to go in an independant function
DataSet ds = LMR.TacticCatList();
return ds.Tables[0];
}
protected void dgTacticSubCatList_ItemDataBound(object sender, DataGridItemEventArgs e)
{
if (e.Item.ItemType == ListItemType.EditItem)
{
//we set the selcted index in the ItemDataBound event
string strID = Request.QueryString[“id”].ToString();
string strSubCatID = dgTacticSubCatList.DataKeys[(int)e.Item.ItemIndex].ToString();
Holder.TacticSubCat tsc = LMR.GetTacticSubCat(strSubCatID);
DropDownList dd = (DropDownList)e.Item.FindControl(“ddTacticCatList”);
dd.SelectedIndex =dd.Items.IndexOf(dd.Items.FindByValue(strID));
}
}
That’s all there is to it. The tricky parts are putting the initial dropdown population in a separate function, and setting the index in the ItemDataBound event.
This post originally appeared on the Stronico blog – with the absorption of Stronico into Digital Tool Factory this post has been moved to the Digital Tool Factory blog
