title: Android FragmentManager lifecycle
body: <p>I am a beginner of Android development. I have a question when FragmentManager is detroyed? I have called the method: "registerFragmentLifecycleCallbacks(FragmentLifecycleCallbacks cb, boolean recursive)" on activity onCreate, I find the official comment of "All registered callbacks will be automatically unregistered when this FragmentManager is destroyed". but when the FragmentManager destroyed？ 
  Thank you in advance!</p>
  
  <p><a href="https://developer.android.com/reference/android/app/FragmentManager.html#registerFragmentLifecycleCallbacks(android.app.FragmentManager.FragmentLifecycleCallbacks,%20boolean)" rel="nofollow noreferrer">FragmentManager#registerFragmentLifecycleCallbacks()</a></p>
  
  <p>and All registered callbacks will be automatically unregistered when this FragmentManager is destroyed. but unregisterFragmentLifecycleCallbacks is NOT called.
  <a href="https://developer.android.com/reference/android/app/FragmentManager.html#unregisterFragmentLifecycleCallbacks(android.app.FragmentManager.FragmentLifecycleCallbacks)" rel="nofollow noreferrer">FragmentManager#unregisterFragmentLifecycleCallbacks()</a></p>