Getting control from Repeater ItemTemplate server-side

Question

I'm trying to use a repeater to make a table. however, there's some logic that I need to implement to some specific controls, says a div, in the items in the repeater.

I've tried this but it didn't work,,, I alwas get:

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Error:

Line 35:         HtmlGenericControl myDiv = (HtmlGenericControl)e.Item.FindControl("RepeaterBG");
Line 36: 
Line 37:         myDiv.Style.Add("background-color","green");
Line 38:     }
Line 39: }

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

My Html is:

<asp:Repeater runat="server" ID="MyStudents"
        OnItemDataBound="rptArticleContent_ItemDataBound">
            <HeaderTemplate>
                <table><tr>
            </HeaderTemplate>
            <ItemTemplate> 

                <td>
                    <div  runat="server" ID="RepeaterBG" > helli there</div>
                    <asp:Label ID="Label1" runat="server" Text='<%# Bind("Name") %>'></asp:Label>
                </td>
                <td>
                    <asp:Label ID="Label2" runat="server" Text='<%# Bind("RegistrationDate") %>'></asp:Label>
                </td>
                <td>
                    <asp:Label ID="Label3" runat="server" Text='<%# Bind("Email") %>'></asp:Label>
                </td>

            </ItemTemplate>
            <FooterTemplate>
                </tr></table>
            </FooterTemplate>
        </asp:Repeater>

my .CS

protected void rptArticleContent_ItemDataBound(object sender, RepeaterItemEventArgs e)
{
    Label lb = new Label();
    lb.Text = "</tr><tr>";
    e.Item.Controls.Add(lb);

    HtmlGenericControl myDiv = (HtmlGenericControl)e.Item.FindControl("RepeaterBG"); // i get null here, it seems to not find it at all!
    myDiv.Style.Add("background-color","green"); // problem here
}

where did i go wrong?!

Answer 1

You need to check and make sure your item is a data item. If you see in your example link you posted, the first line inside the ItemDataBound event is:

if (e.Item.ItemType != ListItemType.Item && e.Item.ItemType !=   
       ListItemType.AlternatingItem) return;

IIRC, that's because the first item inside of the ItemDataBound event is a header item. You must do a check to see if the item is a data item.

Answer 2

You should probably check the item type as to not "search in the header" for instance

protected void rptArticleContent_ItemDataBound(object sender, RepeaterItemEventArgs e)
    if (e.Item.ItemType == ListItemType.Item ||
        e.Item.ItemType == ListItemType.AlternatingItem) {
        // search for control here
    }
}

Answer 3

You cant get items from inside a repeater at runtime in that way, as the controls in a repeater are added after your code is executed.

Instead, you will need to do your FindControl on the individual item in the as it is databound. To do this, set an onItemDataBound event on your repeater, and do your logic in the event that fires for each item. You can find the controls in your item template in the event arguments' item property.

For example:

on your repeater:

<asp:Repeater id="Repeater1" OnItemDataBound="Repeater1OnItemDataBound" runat="server">

in your codebehind:

Public void Repeater1OnItemDataBound(Object Sender, RepeaterItemEventArgs e) {
    HtmlGenericControl myDynamicRepeaterControl = 
     ((HtmlGenericControl)e.Item.FindControl("MyDiv"))
    //...do some work on myDynamicRepeaterControl 
}