Question

I hope someone could help me with this. I wasn’t able to find the ImageButton control inside the ListView, it always gives me Object reference not set to an instance of an object error.

The scenario is, if I checked the checkbox, I wanted the imagebutton to change its’ image. The Checkbox does not reside inside the Listview ItemTemplate. Here’s my code behind for the checkbox_checkchanged event:

   if (cb.Checked)
    {
        foreach (Control c in lv.Controls)
        {
            ImageButton btndel = (ImageButton)c.FindControl("btnDelete");
            btndel.ImageUrl = "~/images/activate.png";
        }
     }

Note: I used ForEach Loop thinking that the btnDelete button appears several times in my Listview.

Answer 1

If the Checkbox is outside of the ListView, the best way would be to use ListView’s ItemCreated-Event:

protected void LV_ItemCreated(object sender, ListViewItemEventArgs e)
{
  // Retrieve the current item.
  ListViewItem item = e.Item;

  // Verify if the item is a data item.
  if (item.ItemType == ListViewItemType.DataItem && cb.Checked)
  {
    ImageButton btndel = (ImageButton)item.FindControl("btnDelete");
    btndel.ImageUrl = "~/images/activate.png";
  }
}

You don’t need to handle the Checkbox’ CheckedChanged-Event but only need to add the OnItemCreated-handler on your aspx markup:

<asp:ListView ID="LV" OnItemCreated="LV_ItemCreated" ... />

On this way you prevent multiple iterations of the ListView-Items. ItemCreated will anyway be called implicitely on every postback to recreate the ListView-Items.