const
  WM_MouseEnter = $B013;
  WM_MouseLeave = $B014;
type
  TfrmMain = class(TForm)
       .
       .
    Timer1: TTimer;
    procedure Timer1Timer(Sender: TObject);
  protected
    procedure WMMouseEnter(var Msg: TMessage); message WM_MouseEnter;
  end;
implementation
{$R *.dfm}

procedure TfrmMain.WMMouseEnter(var Msg: TMessage);
begin
  if(Top<0) then
  begin
    Top := 0;
    //为保证下拉窗体后呈现在最前面
    SetWindowPos(Handle,HWND_TOPMOST, 0, 0, 0, 0, SWP_NOMOVE or SWP_NOSIZE); //将窗体推到最前
    SetWindowPos(Handle,HWND_NOTOPMOST, 0, 0, 0, 0, SWP_NOMOVE or SWP_NOSIZE);//然后取消窗体最前
  end;
  Timer1.Enabled := True;
end;
//依赖定时器定时检查鼠标是否还在窗体范围内，这样此能避免因为快速移动鼠标而丢失MOUSELEAVE事件
procedure TfrmMain.Timer1Timer(Sender: TObject);
var
  rc:TRECT;
  pt:TPOINT;
begin
   GetWindowRect(self.Handle,rc); //取窗体的矩形区域
   GetCursorPos(pt); //取得当前鼠标所在位置
   if(not PtInRect(rc,pt)) then //如果鼠标不在窗体范围内
   begin
      if(Top = 0) then //如果目前窗体正吸附在屏幕上沿，则上移隐藏窗体
      begin
         Top := 0-Height+2;
      end;
      Timer1.Enabled := False; //窗体隐藏后定时器关闭
      SetWindowPos(Handle,HWND_TOPMOST, 0, 0, 0, 0, SWP_NOMOVE or SWP_NOSIZE); //将窗体推到最前
   end;
end;