Drawing on Controls

I am not much of a desktop developer, but I have been getting into it with windows forms and C#.. and I have run into something that seems perplexing to me.

I am creating a windows control that derives from ListView, and I am adding drag and drop functionality that will draw a line between items in the list to indicate where an item that is dropped will be inserted.

My original approach was that upoin DragEnter being fired, I would set a Bitmap that is a priv class member to the current bitmap of the control.. I am doing this like so:

this.ctrlbmp = new Bitmap(this.Width, this.Height, this.CreateGraphics());

Then each time the DragOver event fires, I calculate based on the current Y position of the mouse, where to draw my line, and draw the bitmap on top of the control like such:

this.CreateGraphics().DrawImage(bmp,0,0,this.Width,this.Height);

I would then call this.Refresh() when DragLeave fires.

The problem I have gotten into, seems to have to do with invalidating the control. The effect I get is that each line draws but is never removed as I drag across the list. I thought that it would be taken care of by repainting the entire control each time.

If anyone can suggest reference material, or perhaps explain a more experienced approach, I would appreciate it greatly.

Well.. I couldn't stand this so when I got home I spent a little time working with it and realized that the best approach in my case is to track which item was last targetted and invalidate the region that I had painted over. It now works well and is much less intensive on resources. Something like this:

      Graphics g = this.CreateGraphics();
      Point currentpoint = this.PointToClient(new Point(e.X,e.Y));

      foreach(ListViewItem item in this.Items)
      {
        if(currentpoint.Y <= item.Bounds.Bottom && currentpoint.Y >= item.Bounds.Top)
        {
          if(item.Index != this.lastindextargetted)
          {
            g.DrawLine(new Pen(Brushes.Black,2),0,item.Bounds.Bottom,this.Width,item.Bounds.Bottom);
            if(this.lastindextargetted >= 0)
            {
              this.Invalidate(new Rectangle(0,this.Items[this.lastindextargetted].Bounds.Bottom-2,this.Width,4));
            }

            this.lastindextargetted = item.Index;
          }
        }
      }