how to populate programmatically a dropdownlist in a template?

  • Thread starter Thread starter Chris
  • Start date Start date
C

Chris

Hi,

i defined a dropdownlist in the EditTemplate of a gridview like this:
<asp:TemplateField HeaderText="min" SortExpression="min">
<EditItemTemplate>
<asp:DropDownList ID="DropDownList1" runat="server" SelectedValue='<%#
Bind("min") %>' >
</asp:DropDownList>
</EditItemTemplate>
<ItemTemplate>
<asp:Label ID="Label2" runat="server" Text='<%# Bind("min") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>

Now i want to populate that dropdownlist programmatically because the values
go from 0 to 2OO (it would be fastidious to do that manually).
I tried this in code-behind (vb.net)
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs)
Handles Me.Load
Dim gv As GridView
Dim dd As DropDownList
Dim z As ListItem
Dim i As Integer

gv = form1.FindControl("gridview1")
dd = gv.FindControl("dropdownlist1")
If Not Page.IsPostBack Then
For i = 0 To 200
z = New ListItem(i, i)
dd.Items.Add(z)
Next
End If
End Sub

But this gives this error at runtime: "Object reference not set to an
instance of an object."
at line: dd.Items.Add(z)

What's wrong in my code? I could do this with succes when the dropdownlist
was just in Form1 and not in a template.
Thanks for help
Chris
 
Chris said:
Hi,

i defined a dropdownlist in the EditTemplate of a gridview like this:
<asp:TemplateField HeaderText="min" SortExpression="min">
<EditItemTemplate>
<asp:DropDownList ID="DropDownList1" runat="server" SelectedValue='<%#
Bind("min") %>' >
</asp:DropDownList>
</EditItemTemplate>
<ItemTemplate>
<asp:Label ID="Label2" runat="server" Text='<%# Bind("min")
%>'></asp:Label> </ItemTemplate>
</asp:TemplateField>

Now i want to populate that dropdownlist programmatically because the
values go from 0 to 2OO (it would be fastidious to do that manually).
I tried this in code-behind (vb.net)
Protected Sub Page_Load(ByVal sender As Object, ByVal e As
System.EventArgs) Handles Me.Load
Dim gv As GridView
Dim dd As DropDownList
Dim z As ListItem
Dim i As Integer

gv = form1.FindControl("gridview1")
dd = gv.FindControl("dropdownlist1")
If Not Page.IsPostBack Then
For i = 0 To 200
z = New ListItem(i, i)
dd.Items.Add(z)
Next
End If
End Sub

But this gives this error at runtime: "Object reference not set to an
instance of an object."
at line: dd.Items.Add(z)

What's wrong in my code? I could do this with succes when the
dropdownlist was just in Form1 and not in a template.
Thanks for help
Chris
Click to expand...

First of all, Page_Load is too early for your purposes.
At that time, the GridView has not been databound yet, so there even is no
dropdownlist to fill.
Therefore, move your code to the GridView1_DataBound event.

Secondly, the line
dd = gv.FindControl("dropdownlist1")
will not work, because the dropdownlist is not right in the gridview, but in
one of its cells.
Change it into
dd = gv.Rows(gv.EditItemIndex).Cells(x).FindControl("dropdownlist1")
Replace x by the number of the column that's containing your field with the
dropdownlist.
 
Thanks for replying ...
I get this error with your code: dd =
gv.Rows(gv.EditItemIndex).Cells(x).FindControl("dropdownlist1")

'EditItemIndex' is not a member of 'System.Web.UI.WebControls.GridView'.

Thanks
 
you should populated the dropdownlist in the dropdownlist_load event.
hope this will help.
 
On Sat, 28 Jul 2007 17:04:22 +0200, Chris wrote:

Hello Chris
Did'nt find something in MSDN but
If you have implement an own routine

Public Sub DynFill(ByVal sender As Object, ByVal e As
System.EventArgs)
Dim dd As DropDownList = sender
Dim z As ListItem
Dim i As Integer

If Not dd Is Nothing Then
If dd.Items.Count = 0 Then
For i = 0 To 200
z = New ListItem(i, i)
dd.Items.Add(z)
Next
End If
End If
End Sub

in your Page

and the control has to be something like

<EditItemTemplate>
<asp:DropDownList Enabled="true"
OnLoad="DynFill" ID="DropDownList1" runat="server" SelectedValue='<%#
Bind("Rate") %>'>
</asp:DropDownList>
</EditItemTemplate>

so your code will be executed.

HtH


Norman Goetz
 
Thanks again, but the dropdownlist is in a templatefield and there is no
dropdownlist1_onload event ...
 
right click the gridview, select "edit template",
select the column where the dropdownlist exist,
now you could set the properties and events of the
dropdownlist
 
Hi again,

i did what you told me like this:
Protected Sub DropDownList2_Load(ByVal sender As Object, ByVal e As
System.EventArgs)
Dim dd As DropDownList
Dim gv As GridView
Dim z As ListItem
Dim i As Integer
gv = form1.FindControl("gridview1")
dd = gv.FindControl("dropdownlist2") 'this must be a problem i think
If Not Page.IsPostBack Then
For i = 0 To 200
z = New ListItem(i, i)
dd.Items.Add(z)
Next
End If
End Sub

in aspx i have:
<asp:DropDownList ID="DropDownList2" runat="server" SelectedValue='<%#
Bind("min") %>'
OnLoad="DropDownList2_Load">
</asp:DropDownList>

But this gives (i think because of line: dd =
gv.FindControl("dropdownlist2")
"DropDownList2' has a SelectedValue which is invalid because it does not
exist in the list of items.
Parameter name: value"

If i suppress the line: If Not Page.IsPostBack Then
i get: "Object reference not set to an instance of an object."
 
you should get the reference of DropDownList2
by converting parameter sender to DropDownList.

Here is some C# code for you, you could turn it
into VB code.And make the binding value exist in
the range of 0 to 200.

DropDownList ddl =(DropDownList)sender;
IF (!IsPostBack)
{
for(int i=0;i<200;i++)
ddl.items.Add(new ListItem(i.ToString(),i.ToString());
}
 
On Sun, 29 Jul 2007 20:15:42 +0200, Chris wrote:
Hi Chris,
i did what you told me like this:
Click to expand...
you did not:
the following code is wrong !
gv = form1.FindControl("gridview1")
dd = gv.FindControl("dropdownlist2") 'this must be a problem i think
Click to expand...
that's functional:
dd=sender

the filling is a postback, instead of use the Count of Items t see if
the routine has to fill:
If Not Page.IsPostBack Then
Click to expand...
If dd.Items.Count=0 then
....
Hth

Norman Goetz
 
Thanks, i'll try

chenhong said:
you should get the reference of DropDownList2
by converting parameter sender to DropDownList.

Here is some C# code for you, you could turn it
into VB code.And make the binding value exist in
the range of 0 to 200.

DropDownList ddl =(DropDownList)sender;
IF (!IsPostBack)
{
for(int i=0;i<200;i++)
ddl.items.Add(new ListItem(i.ToString(),i.ToString());
}
Click to expand...
 
Chris said:
Thanks for replying ...
I get this error with your code: dd =
gv.Rows(gv.EditItemIndex).Cells(x).FindControl("dropdownlist1")

'EditItemIndex' is not a member of
'System.Web.UI.WebControls.GridView'.
Click to expand...

Sorry, it should be EditIndex.
 
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