ASP.Net - Getting data from RepeaterItem

Question

I'm pretty new to ASP.Net and I'm not sure I'm going about this the right way. I have a Repeater which is bound to a list of "Image" objects. Within each RepeaterItem is a checkbox and I have a button OnClick event, which I want to display some attributes of the checked Image objects.

The label updates, but the metadata is blank. DataBinder.Eval(i.DataItem, "FileName") is coming back null, but I'm not sure why? I thought perhaps the postback from the checkbox was causing problems but I still get the same issue if I try to display the data before any postbacks have occurred, so perhaps I'm not fetching the attributes correctly. Or am I going about this in completely the wrong way? Any help appreciated.

Code:

protected void Page_Load(object sender, EventArgs e)
{
    if (!Page.IsPostBack)
    {
        string importPath = Server.MapPath("~/Images/ForImport");
        ImageProcessor processor = new ImageProcessor(importPath);

        rptImageList.DataSource = processor.ImageList;
        rptImageList.DataBind();
    }
}

protected void btnImport_Click(object sender, EventArgs e)
{
    foreach (RepeaterItem i in rptImageList.Items)
    {
        CheckBox chk = i.FindControl("chkSelectImage") as CheckBox;
        if (chk.Checked)
        {
            Testlabel.Text += "Selected: " + DataBinder.Eval(i.DataItem, "FileName");
        }
    }
}

HTML:

<asp:Repeater ID="rptImageList" runat="server">
    <ItemTemplate>
    <div class="photoinstance">
        <asp:Image runat="server" ImageUrl='<%#"Images/ForImport/" +DataBinder.Eval(Container.DataItem, "FileName") %>' />
        <asp:CheckBox ID="chkSelectImage" AutoPostBack="true" runat="server"/>
        <p><%#Eval("FileName")%> - <%#Eval("FileSize")%> bytes</p>
        </div>
    </ItemTemplate>
</asp:Repeater>

Answer 1

i.DataItem is not available (is null) at btnImport_Click, is available only at the ItemDataBound event (if I recall correctly the event name).
You can use a HiddenField to store the FileName then you will have to call i.FindControl.

Answer 2

I think this question is asking how to get data from a repeater on postback and more specifically how to interact with a CheckBox that is within a repeater. So on the postback of another control an example of how to do this is;

    protected void CheckBox_CheckedChanged(object sender, EventArgs e)
    {
        foreach (RepeaterItem ri in Repeater.Items)
        {
            foreach (Control c in ri.Controls)
            {
                if (typeof(CheckBox) == c.GetType())
                {
                    CheckBox checkBox = (CheckBox)c;
                    checkBox.Checked = true;
                }
            }
        }
    }