请问为什么会这样？

[summernightrain]

我在DataGrid中放了一个TemplateColumn,里面是一个DropDownList，然后我用代码访问这个DropDownList，下面是我在EditCommand中写的代码，我想在点编辑按钮的时候给这个DropDownList加入数据源，结果总是无法得到这个对象的正确引用。dt总是等于空。
<HTML代码>
<asp:TemplateColumn HeaderText="部门">
<EditItemTemplate>
<asp:DropDownList id="editDepart" runat="server" Width="173px"> </asp:DropDownList> </EditItemTemplate>
</asp:TemplateColumn>

Private Sub DataGrid1_EditCommand(ByVal source As Object, ByVal e As System.Web.UI.WebControls.DataGridCommandEventArgs) Handles dgUsers.EditCommand

dgUsers.EditItemIndex = e.Item.ItemIndex
Dim dt As DropDownList = CType(e.Item.Cells(6).FindControl("editDepart"), DropDownList)
If dt Is Nothing Then
Label1.Text = "Edit:dt is null"
Else
dt.DataSource=....
dt.DataBind()
End If

End Sub

[icyer]

dgUsers.EditItemIndex = e.Item.ItemIndex
dgUsers.DataBind()
Dim dt As DropDownList = CType(dgUsers.Items(e.Item.ItemIndex).FindControl("editDepart"), DropDownList)

[大健]

Private Sub DataGrid1_ItemDataBound(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.DataGridItemEventArgs) Handles DataGrid1.ItemDataBound

Dim i as Integer
Dim MyItem As System.Web.UI.WebControls.ListItem
'如果该列正被编辑，则
If DataGrid1.EditItemIndex = e.Item.ItemIndex Then
For i = 0 To 10
MyItem = New System.Web.UI.WebControls.ListItem()
MyItem.Text = i.ToString
MyItem.Value = i.ToString
CType(e.Item.Cells(3).FindControl("editDepart"),DropDownList).Items.Add(MyItem)
MyItem = Nothing
Next
End If

End Sub