学步园

系统设备变化，系统向应用程序发出WM_DEVICECHANGE消息，应用程序注册一个消息处理函数，来获取设备变化通知.

unit   Unit1; 
  
interface 
  
uses 
      Windows,   Messages,   SysUtils,   Variants,   Classes,   Graphics,   Controls,   Forms, 
      Dialogs,   AppEvnts,   ExtCtrls,   StdCtrls; 
  
type 
      TForm1   =   class(TForm) 
          Label1:   TLabel; 
      private 
          {   Private   declarations   } 
          procedure   WMDeviceChange(var   Msg:   TMessage);   message   WM_DEVICECHANGE; 
      public 
          {   Public   declarations   } 
      end; 
  
var 
      Form1:   TForm1; 
  
implementation 
  
{$R   *.dfm} 
  
procedure   TForm1.WMDeviceChange   (var   Msg:   TMessage); 
var 
      myMsg   :   String; 
begin 
      Case   Msg.WParam   of 
      32768: 
          begin 
              myMsg   :='USB设备插入'; 
              Label1.Caption:=myMsg 
          end; 
      32772: 
          begin 
              myMsg   :='USB设备拔出';  
              Label1.Caption:=myMsg; 
          end; 
      end; 
end; 
  
end.