Question

I have a asp.net repeater control in a aspx page, with runat=”server” and an id set, however for some reason i can’t access its ID from code behind (I can access the id of the asp:detaislview control it sits in though). So instead in the page_load method I am doing the following:

Repeater repeater = (Repeater)PromotionSitesDetailsView.FindControl("estateRepeater");
repeater.DataSource = estateList;

However when run, an error comes up saying the repeater is null! All I want to do is set the datasource of this repeater to a List object. Any ideas?

Answer 1

You said the Repeater sits inside a DataList. The DataList is, itself, a kind of repeater – the controls inside of it don’t exist until the DataList is bound to a datasource, and the controls in the template are created once per item in the source. So if you bind the DataList to a source with 3 items, you will get 3 repeaters.

So it looks kind of like this:

Page
    MyDataList
        Item0
            MyRepeater
        Item1
            MyRepeater
        Item2
            MyRepeater

So obviously MyDataList.FindControl("MyRepeater") can’t work – which “MyRepeater” are we talking about? Since multiple controls cannot have the same ID, ASP.NET solves this by making the ID unique to something called a NamingContainer. Since the DataList repeats the same set of controls many times (once per item in the data source), each item in the DataList is a NamingContainer.

We need to find the NamingContainer we know holds the instance of MyRepeater that we want:

MyDataList.Items[0].FindControl("MyRepeater");

You can iterate over the items in the DataList after it has been bound (of course, before it has been bound it has no items). You can also operate on a given item in the DataList as that item is being created:

<asp:DataList OnItemDataBound="MyDataList_HandleItemDataBound" ... />

//this will get called once per item as it is created
void MyDataList_HandleItemDataBound(object sender, DataListItemEventArgs e)
{
    //e.Item is the current item being databound
    Repeater myRepeater = e.Item.FindControl("MyRepeater") as Repeater;
    myRepeater.DataSource = //ds
    myRepeater.DataBind();
}