以下是一段抓屏的代码，我把这些词句复制到一个服务程序时里，为什么只得到一个白屏，
好像是只本就没有抓到屏
var
    Fullscreen:Tbitmap;
    FullscreenCanvas:TCanvas;
    dc:HDC;
begin
    Fullscreen:=TBitmap.Create;
    //创建一个BITMAP来存放图象
    Fullscreen.Width:=screen.width;
    Fullscreen.Height:=screen.Height;
    DC:=GetDC(0);
    //取得屏幕的DC，参数0指的是屏幕
    FullscreenCanvas:=TCanvas.Create;
    //创建一个CANVAS对象
    FullscreenCanvas.Handle:=DC;

    Fullscreen.Canvas.CopyRect(Rect(0,0,screen.Width,screen.Height),
              fullscreenCanvas,Rect(0,0,Screen.Width,Screen.Height));
    //把整个屏幕复制到BITMAP中
    FullscreenCanvas.Free;
    //释放CANVAS对象
    ReleaseDC(0,DC);
    //释放DC

    Image1.Picture.Bitmap:=fullscreen;
    //拷贝下的图象赋给IMAGE对象
    Image1.Width:=fullscreen.Width;
    Image1.Height:=fullscreen.Height;
    fullscreen.free;
    //释放bitmap
end;