检测USB使用情况

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此方法放在任何地方,都可以正常.

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procedure TForm1.usb(var msg: TMessage);
const
  DBT_DEVICEARRIVAL = $8000;
  DBT_DEVICEREMOVECOMPLETE = $8004;
  DBT_DEVNODES_CHANGED = $0007;
begin
  case msg.WParam of
     DBT_DEVICEARRIVAL:ShowMessage('insert');//增加了新硬件
     DBT_DEVICEREMOVECOMPLETE:ShowMessage('remove') ;
     DBT_DEVNODES_CHANGED:
  end;
end;

end.