Question

I have a listView that is being updated from multiple threads, with the threads status and id being displayed. When a thread has ended the item is removed.

My problem is that the way i use to update my listView is by using the listViews ID (to locate the subitems i wish to update). Now, as listView items start getting removed i run into problems because that ID for a specific thread has changed..

Here is the code i currently use to update and remove:

    private void AddToListViewThread(string user, string status, int threadNumber)
    {
        Invoke(new MethodInvoker(
                       delegate
                       {
                           listView2.BeginUpdate();
                           this.listView2.Items[threadNumber].SubItems[1].Text = user;
                           this.listView2.Items[threadNumber].SubItems[2].Text = status;
                           listView2.EndUpdate();
                       }
                       ));
    }

    private void RemoveFromListViewThread(int threadNumber)
    {
        Invoke(new 
            MethodInvoker(
                       delegate
                       {
                           listView2.BeginUpdate();
                           this.listView2.Items.RemoveAt(threadNumber);
                           listView2.EndUpdate();
                       }
                       ));
    }

I now understand that i cannot use the threadNumber as the item index (as items get removed) is there any other way i could achieve this? maybe by targeting the “user” subitem? and then getting subitems from that?

Answer 1

Use the tag property of the ListViewItem to store a different index (similar to the SQL autoincrement ).

The Tag property is a field used to store metadata about the item.

A simple binary search would let you find the item to remove in Log(n) time.

Your code would looks like this:

private void AddToListViewThread(string user, string status, int threadNumber)
{
    Invoke(new MethodInvoker(
                   delegate
                   {
                       listView2.BeginUpdate();
                       int i = SearchItem(listView2, threadNumber);
                       if ( i > -1)
                       {
                       this.listView2.Items[i].SubItems[1].Text = user;
                       this.listView2.Items[i].SubItems[2].Text = status;
                       }
                       listView2.EndUpdate();
                   }
                   ));
}

private void RemoveFromListViewThread(int threadNumber)
{
    Invoke(new MethodInvoker(
                   delegate
                   {
                       listView2.BeginUpdate();
                       int i = SearchItem(listView2, threadNumber);
                       if ( i > -1)
                       {
                           this.listView2.Items.RemoveAt(i);
                       }
                       listView2.EndUpdate();
                   }
                   ));
}

private int SearchItem(ListView list, int id)
{ 
         for (int i  = 0; i < list.Items.Count; i++) // I used sequential search but you can implement binary instead
         {
            if (((int)list.Items[i].Tag) == id) return i;
         }
         return -1;
}