Web User Controls: Exposing Items property of contained controls

8 Jul 2005 4:41 PM

Warped

I am trying to make a simple user control that contains a Label and a
DropDownList. Basically, I want this control to expose some of the
Label's properties (e.g. Text) and some of the DropDownList's
properties (e.g. Items) and have the designer handle them
appropriately. Exposing Label.Text wasn't a problem, but I can't get
DropDownList.Items to work. I added an Items property to my codebhind
class like this.

public partial class LabelledDropDown : System.Web.UI.UserControl
{

    public ListItemCollection Items
    {
        get { return this.DropDownList1.Items; }
    }
}

When I place an instance of the user control on a web form, the Items
property does appear in the designer, but the designer doesn't treat it
as an editable collection. How do I make that happen?

Also, any items I add to the collection via the designer should be
"remembered" in the .aspx file as nested elements, like this.

        <uc1:LabelledDropDown ID="LabelledDropDown1" runat="server"
LabelText="Screen size">
            <asp:ListItem>Item 1</asp:ListItem>
            <asp:ListItem>Item 2</asp:ListItem>
            <asp:ListItem>Item 3</asp:ListItem>
        </uc1:LabelledDropDown>

This functionality would be relatively simple in .NET WinForms, so I
assume it can be done in WebForms as well.

13 Jul 2005 4:21 PM

Jonathan Mast

Hi Warped,

In your code where you expose the nested DropDownLists Items collection, do
you define a setter?

I'll admit that I've never run into this situation, but that may very well
be your issue.

Try making this code:

     public ListItemCollection Items
     {
         get { return this.DropDownList1.Items; }
     }

Look like this:

    public ListItemCollection Items
    {
         get{ return this.DropDownList1.Items; }
         set{ this.DropDownList1.Items=value; }
    }

Maybe that will make it work for you?

It seems to me that the reason the IDE does not treat it as an editable
collection is because if you don't provide a setter method to a property,
then it is effectively read-only.

Hope it helps.

--
Cheers,

Jonathan

Show quoteHide quote

"Warped" wrote:

> I am trying to make a simple user control that contains a Label and a
> DropDownList. Basically, I want this control to expose some of the
> Label's properties (e.g. Text) and some of the DropDownList's
> properties (e.g. Items) and have the designer handle them
> appropriately. Exposing Label.Text wasn't a problem, but I can't get
> DropDownList.Items to work. I added an Items property to my codebhind
> class like this.
>
> public partial class LabelledDropDown : System.Web.UI.UserControl
> {
>
>     public ListItemCollection Items
>     {
>         get { return this.DropDownList1.Items; }
>     }
> }
>
> When I place an instance of the user control on a web form, the Items
> property does appear in the designer, but the designer doesn't treat it
> as an editable collection. How do I make that happen?
>
> Also, any items I add to the collection via the designer should be
> "remembered" in the .aspx file as nested elements, like this.
>
>         <uc1:LabelledDropDown ID="LabelledDropDown1" runat="server"
> LabelText="Screen size">
>             <asp:ListItem>Item 1</asp:ListItem>
>             <asp:ListItem>Item 2</asp:ListItem>
>             <asp:ListItem>Item 3</asp:ListItem>
>         </uc1:LabelledDropDown>
>
> This functionality would be relatively simple in .NET WinForms, so I
> assume it can be done in WebForms as well.
>
>

15 Jul 2005 1:58 PM

Warped

A setter like that would allow me to replace the entire collection with
a new collection, but that's not what I want. I want to be able to
add/remove individual items to/from the collection. In other words,

MyControl.Items.Add(newItem);

not

MyControl.Items = NewCollectionOfItems;