鼠标拖动窗体

procedure TPreview.ImgTitleMouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
   ReleaseCapture;
   SendMessage(Handle,WM_SYSCOMMAND,$F012,0);
end;

procedure TPreview.ImgTitleDblClick(Sender: TObject);
begin
   if self.WindowState <> wsMaximized then
   self.WindowState := wsmaximized
  else
    self.WindowState := wsNormal;
end;