fragment show hide 方法出现了一点小问题 求指点

Question

在AFragment中
点击Button
FragmentManager fm = getActivity().getFragmentManager();
FragmentTransaction ft = fm.beginTransaction();
ft.hide(AllSingerFragment.this);
ft.add(R.id.id_business_content, bFragment);
ft.commit();
这里执行正常
然后再BFragmen中

AllSingerFragment aFragment = new AFragment();
点击Button
FragmentManager fm = getActivity().getFragmentManager();
FragmentTransaction ft = fm.beginTransaction();
ft.hide(BFragment.this);
ft.show(aFragment);
ft.commit();
这里执行的效果是 B隐藏了A并没有被show出来

                            然后用
                             FragmentManager manager = allSingerFragment.getFragmentManager();
            FragmentTransaction fragmentTransaction = manager.beginTransaction();
            fragmentTransaction.show(aFragment);
            fragmentTransaction.commit();
                            来showAFragment就报错空指针在该方法的第二行，求指点这里是什么原因。。。

Answer 1

https://www.cnblogs.com/jackson-leung/p/5272062.html