为什么用本地硬盘内容填充tvwSource，要先清除所有节点？

Question

为什么用本地硬盘内容填充tvwSource，要先清除所有节点？tvw.Nodes.Clear();

Answer 1

以下是源代码private void FillDirectoryTree(TreeView tvw, bool isSource)
        {
            tvw.Nodes.Clear(); //问题就是这，为什么要先清除结点内容呢，不是还没填充吗？
            string[] strDrives = Environment.GetLogicalDrives();
            foreach (string rootDirectoryName in strDrives)
            {
                try
                {
                    DirectoryInfo dir =
                        new DirectoryInfo(rootDirectoryName);
                    dir.GetDirectories();
                    TreeNode ndRoot = new TreeNode(rootDirectoryName);
                    tvw.Nodes.Add(ndRoot);
                    if (isSource)
                    {
                        GetSubDirectoryNodes(ndRoot, ndRoot.Text, true, 1);
                    }
                    else
                    {
                        GetSubdirectoryNodes(
                            ndRoot, ndRoot.Text, false, 1
                            );
                    }
                }
                    catch
                {
                    
                    }
                Application.DoEvents();
                
            }
        }