C#下載文件時候彈出選擇文件夾保存目錄

//保存文件夾選擇對話框引用
//添加引用system.design.dll   /
using System.Windows.Forms.Design;

private void button4_Click(object sender, System.EventArgs e)
  {

   //選擇文件的保存路徑
   //添加窗體控件folderBrowserDialog1
   DirBrowser   olderBrowserDlg=new   DirBrowser(); 
     
   if (folderBrowserDialog1.ShowDialog()==DialogResult.OK)
   {
    textBox2.Text = folderBrowserDialog1.SelectedPath;
   }

  }

  #region 彈出保存文件夾選擇窗口類
  //一般選擇文件保存地址都用彈出對話框來進行選擇
  public class DirectorySelect : FolderNameEditor
  {
   private FolderBrowser fb = new FolderBrowser();
   private string fDescription = "Choose Directory";
   private string fReturnPath = String.Empty;
 
   public string Description
   {
    set { fDescription = value; }
    get { return fDescription; }
   }
 
   public string ReturnPath
   {
    get { return fReturnPath; }
   }
 
   public DirectorySelect()
   {
 
   }
 
   private DialogResult RunDialog()
   {
    fb.Description = this.Description;
    fb.StartLocation = FolderBrowserFolder.MyComputer;
    fb.Style = FolderBrowserStyles.RestrictToSubfolders;
    //|FolderBrowserStyles.RestrictToDomain;
    return fb.ShowDialog();
   }
 
   public DialogResult ShowDialog()
   {
    DialogResult dRes = DialogResult.None;
    dRes = RunDialog();
    if (dRes == DialogResult.OK)
     this.fReturnPath = fb.DirectoryPath;
    else
     this.fReturnPath = String.Empty;
    return dRes;
   }
  }

  //一般選擇文件保存地址都用彈出對話框來進行選擇
  //調用  
  //DirBrowser   myDirBrowser=new   DirBrowser();  
  //if(myDirBrowser.ShowDialog()!=DialogResult.Cancel)  
  //MessageBox.Show(myDirBrowser.ReturnPath);  

  public   class   DirBrowser   :   FolderNameEditor    
  {    
   FolderBrowser   fb   =   new   FolderBrowser();    
   public   string   Description    
   {    
    set   {   _description   =   value;   }    
    get   {   return   _description;   }    
   }    
     
   public   string   ReturnPath    
   {    
    get   {   return   _returnPath;   }    
   }    
     
   public   DirBrowser()   {   }    
   public   DialogResult   ShowDialog()    
   {    
    fb.Description   =   _description;    
    fb.StartLocation   =   FolderBrowserFolder.MyComputer;    
    DialogResult   r   =   fb.ShowDialog();    
    if   (r   ==   DialogResult.OK)    
     _returnPath   =   fb.DirectoryPath;    
    else    
     _returnPath   =   String.Empty;    
     
    return   r;    
   }    
   
   //private   string   _description   =   "Choose   Directory";    
   //private   string   _returnPath   =   String.Empty; 
   private   string   _description   =   "請選擇文件夾";    
   private   string   _returnPath   =   String.Empty; 
  }

  #endregion