ListView和ImageList清除不工作

我正在开发一个程序，使用listView和ImageList来显示本地文件夹中的图像。我面临的问题是:我的代码有lstView_un.Items.Clear();方法在导入任何图像之前清除列表视图的内容。但是它会将以前的内容附加到新加载的或将来加载的图像上。甚至我已经检查过清除listview与按钮，不清除任何东西。

有什么问题吗?请帮我解决这个问题!

整个代码是:

 lstView_un.Items.Clear();
                DateTime d1 = DateTime.Now;
                DateTime d2 = dtp_unlist.Value;
                TimeSpan t = d1 - d2;
                double NrOfDays = t.TotalDays;

                DateTime dt = DateTime.Now.AddDays(-NrOfDays);
                lstView_un.Items.Clear();
                string imagesPath = @"D:'Face Recognition System'UnknownFace";
                string[] extensions = new[] { ".jpg", ".jpeg", ".png" };
                var allfiles = Directory.GetFiles(imagesPath);
                List<FileInfo> files = new List<FileInfo>();
                foreach (string f in allfiles) files.Add(new FileInfo(f));
                var filesSorted = files.Where(f => extensions.Contains(f.Extension.ToLower()))
                                       .Where(f => f.CreationTime < dt)
                                       .OrderByDescending(f => f.CreationTime);
                this.imageList1.ImageSize = new Size(256, 250);
                this.imageList1.ColorDepth = ColorDepth.Depth32Bit;
                foreach (FileInfo fileInfo in filesSorted)
                {
                    try
                    {
                        this.imageList1.Images.Add(fileInfo.Name,
                                                 Image.FromFile(fileInfo.FullName));
                    }
                    catch
                    {
                        Console.WriteLine(fileInfo.FullName + "  is is not a valid image.");
                    }
                }
                this.lstView_un.View = View.LargeIcon;
                lstView_un.LargeImageList = this.imageList1;
                lstView_un.Items.Clear();
                for (int j = 0; j < this.imageList1.Images.Count; j++)
                {
                    ListViewItem item = new ListViewItem();
                    item.ImageIndex = j;
                    item.Text = imageList1.Images.Keys[j].ToString();
                    this.lstView_un.Items.Add(item);
                }       

        lstView_un.SmallImageList.Images.Clear();
        lstView_un.LargeImageList.Images.Clear();