Unbalanced calls to begin/end appearance transitions for <UIPageViewController:

 當手動來轉換至UIPageViewController時,若出現Unbalanced calls to begin/end appearance transitions for UIPageViewController:,這表示兩個UIPageViewController不當重疊。

解決方法:

找到這一行,並去掉這一行

[[self view] addSubview:[pageController view]];