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        lv_files.BeginUpdate();

        lv_files.LargeImageList = imageList1;

        progressBar1.Maximum = lv_files.Items.Count;
        progressBar1.Value = 0;
        foreach (ListViewItem lvi in lv_files.Items)
        {
          string file = ((Resizer)lvi.Tag).Sourcefile;

          if (!imageList1.Images.ContainsKey(file))
          {
            Bitmap oldBmp = (Bitmap)Bitmap.FromFile(file);                 

            Image im = oldBmp.GetThumbnailImage(imageList1.ImageSize.Width, imageList1.ImageSize.Height, delegate { return false; }, IntPtr.Zero);
                        
                imageList1.Images.Add(file, im);
          }

          lvi.ImageKey = file;

          progressBar1.Value += 1;
          Application.DoEvents();
        }

        lv_files.EndUpdate();