DataGridView vertical scrollbar not updating properly (Forms bug?)

Question

I\'ve encountered a bug (I assume) in .NET 3.5. When adding rows to a DataGridView using Rows.Add(), while the DGV is disabled, the vertical scrollbar doesn\'t update proper

Answer 1

I found your post while searching for a fix for the issue I was having. What I encountered on my Microsoft Surface (Win10) was the inability to vertical scroll the DataGridView to the very last line of a long list using a touch gesture (like flick). Frequently, the last line was maddeningly hard to get to. The solution was simple but took me a while to figure out. I'm leaving it here in case it's helpful.

// Override WndProc in your custom class inherited from DataGridView
protected override void WndProc(ref Message m)
{
  switch (m.Msg)
  {
    case 0x115:// WM_VSCROLL
      // The low-order word holds the command
      uint cmd = ((uint)m.WParam & (uint)0x0000FFFF);
      switch (cmd)
      {
        case 5: // SB_THUMBTRACK
          if (Rows.Count > 0)
          {
            // The high-order word holds the position
            uint pos = ((uint)m.WParam & (uint)0xFFFF0000) >> 16;

            // SAVE: This would give us the "true" ratio based on 100%
            // SAVE: double ratio = (double)pos / (double)(VerticalScrollBar.Maximum - VerticalScrollBar.LargeChange);
            // SAVE: Debug.WriteLine("Scroll Position: " + pos + "\t" + (ratio * 100.0).ToString("F2") + "%");

            // What we want is the ratio to the TOP of the thumb, BECAUSE
            // THIS GIVES US THE RATIO TO THE FIRST LINE INDEX
            double firstLineRatio = (double)pos / (double)(VerticalScrollBar.Maximum);
            // We want to make it so that it shows the full line 
            // even if we just barely meet the ratio
            double dFirstLine = firstLineRatio * Rows.Count;
            int iFirstLine = (int)(dFirstLine + 0.9999);
            // SAVE: Debug.WriteLine("Scroll Position: " + pos + "\t" + (ratio * 100.0).ToString("F2") + "%");
            FirstDisplayedScrollingRowIndex = iFirstLine;
            // We do this INSTEAD OF the default for this message, so RETURN
            return;
          }
          break;
      }
      break;
    default:
      break;
  }
  base.WndProc(ref m);
}