列表框项目颜色错误

我想给每组文件名一个不同的颜色，但是在该代码中只有第一个文件名将具有不同的颜色，调试代码时，我找不到任何错误，问题出在哪里？。。。

public class ListBoxEx : ListBox
 {
  private string PreviousText = string.Empty;
  private string CurrentText = string.Empty;
  private bool equal = false;
  public ListBoxEx()
  {
     this.DrawMode = DrawMode.OwnerDrawFixed;
  }
  protected override void OnDrawItem(DrawItemEventArgs e)
  {
   try
   {
    e.DrawBackground();
    if (this.Items.Count > 0 && e.Index > 0)
    {
      PreviousText = Path.GetFileName(this.Items[e.Index - 1].ToString());
      CurrentText = Path.GetFileName(this.Items[e.Index].ToString());
      if (CurrentText == PreviousText)
       equal = true;
      else equal = false;
      if (equal)
       e.Graphics.FillRectangle(new SolidBrush(Color.LightYellow), e.Bounds);
      else
       e.Graphics.FillRectangle(new SolidBrush(Color.LightBlue), e.Bounds);
      e.Graphics.DrawString(this.Items[e.Index].ToString(), e.Font, new SolidBrush(Color.Black), new PointF(e.Bounds.X, e.Bounds.Y));
  base.OnDrawItem(e);
    }
   }
   catch (Exception ex)
    {
    throw (ex);
   }
  }
 }

  string tempFilename = string.Empty;
  SolidBrush Brushcolor;
  bool colorSwitch = false;
protected override void OnDrawItem(DrawItemEventArgs e)
{
 e.DrawBackground();
// Group colors
   string text = this.Items[e.Index].ToString();
   string filename = Path.GetFileName(text);
    if (filename == tempFilename)
     equal = true;
    else equal = false;
    if (equal)
     Brushcolor = ExChangeBrush(!colorSwitch);
    else
    {
     Brushcolor = ExChangeBrush(colorSwitch);
     colorSwitch = !colorSwitch;
    }
    tempFilename = filename;
// end Group colors
   e.Graphics.FillRectangle(Brushcolor, e.Bounds);
   e.Graphics.DrawString(text, e.Font, new SolidBrush(Color.Black), new PointF(e.Bounds.X, e.Bounds.Y));
   base.OnDrawItem(e);
  }