在USB端口被热插后，系统会向所有
程序发布WM_DEVICECHANGE消息，所以只要捕获此消息即可实现对U盘的监视。
1、新建工程;
2、在form1上放一个Label;
3、定义一个私有过程 procedure WMDeviceChange(var Msg: TMessage); message WM_DEVICECHANGE;
完整代码如下：
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 :='U盘插入';
Label1.Caption:=myMsg
end;
32772:
begin
myMsg :='U盘拔出';
Label1.Caption:=myMsg;
end;
end;
end;
end.
