namespace   U盘更新   
  {   
          public   partial   class   Form1   :   Form   
          {   
                  public   const   int   WM_DEVICECHANGE   =   0x219;   
                  public   const   int   DBT_DEVICEARRIVAL   =   0x8000;   
                  public   const   int   DBT_CONFIGCHANGECANCELED   =   0x0019;   
                  public   const   int   DBT_CONFIGCHANGED   =   0x0018;   
                  public   const   int   DBT_CUSTOMEVENT   =   0x8006;   
                  public   const   int   DBT_DEVICEQUERYREMOVE   =   0x8001;   
                  public   const   int   DBT_DEVICEQUERYREMOVEFAILED   =   0x8002;   
                  public   const   int   DBT_DEVICEREMOVECOMPLETE   =   0x8004;   
                  public   const   int   DBT_DEVICEREMOVEPENDING   =   0x8003;   
                  public   const   int   DBT_DEVICETYPESPECIFIC   =   0x8005;   
                  public   const   int   DBT_DEVNODES_CHANGED   =   0x0007;   
                  public   const   int   DBT_QUERYCHANGECONFIG   =   0x0017;   
                  public   const   int   DBT_USERDEFINED   =   0xFFFF;   
    
                  public   Form1()   
                  {   
                          InitializeComponent();   
                  }   
    
                  private   void   Form1_Load(object   sender,   EventArgs   e)   
                  {   
    
                  }   
                    
                  protected   override   void   WndProc(ref   Message   m)   
                  {   
                          try   
                          {   
                                  if   (m.Msg   ==   WM_DEVICECHANGE)   
                                  {   
                                          switch   (m.WParam.ToInt32())   
                                          {   
                                                  case   WM_DEVICECHANGE:   
                                                          break;   
                                                  case   DBT_DEVICEARRIVAL://U盘插入   
                                                          DriveInfo[]   s   =   DriveInfo.GetDrives();   
                                                          foreach   (DriveInfo   drive   in   s)   
                                                          {   
                                                                  if   (drive.DriveType   ==   DriveType.Removable)   
                                                                  {   
                                                                          listBox1.Items.Add("U盘已插入,盘符为:"   +   drive.Name.ToString());   
                                                                          break;   
                                                                  }   
                                                          }   
                                                          break;   
                                                  case   DBT_CONFIGCHANGECANCELED:   
                                                          break;   
                                                  case   DBT_CONFIGCHANGED:   
                                                          break;   
                                                  case   DBT_CUSTOMEVENT:   
                                                          break;   
                                                  case   DBT_DEVICEQUERYREMOVE:   
                                                          break;   
                                                  case   DBT_DEVICEQUERYREMOVEFAILED:   
                                                          break;   
                                                  case   DBT_DEVICEREMOVECOMPLETE:   //U盘卸载   
                                                          break;   
                                                  case   DBT_DEVICEREMOVEPENDING:   
                                                          break;   
                                                  case   DBT_DEVICETYPESPECIFIC:   
                                                          break;   
                                                  case   DBT_DEVNODES_CHANGED:   
                                                          break;   
                                                  case   DBT_QUERYCHANGECONFIG:   
                                                          break;   
                                                  case   DBT_USERDEFINED:   
                                                          break;   
                                                  default:   
                                                          break;   
                                          }   
                                  }   
                          }   
                          catch   (Exception   ex)   
                          {   
                                  MessageBox.Show(ex.Message);   
                          }   
                          base.WndProc(ref   m);   
                  }  请问ref是如何得到的 ,多谢回答!!!!!!!!!!!!!!!!!!!!!!!!!