原来我干了件蠢事。我推翻我的活动的onSaveInstanceState（...）方法，而不调用 super.onSaveInstanceState（），这导致在片段不被重建。在这里张贴的答案，希望我能拯救其他人的时候了！

Turns out I did a Stupid Thing. I overrode the onSaveInstanceState(...) method in my activity, without calling super.onSaveInstanceState(), which resulted in the fragments not being recreated. Posting the answer here in hopes that I can save somebody else the time!