Difference and uses of onCreate(), onCreateView() and onActivityCreated()

onCreate():

The onCreate() method in a Fragment is called after the Activity's onAttachFragment() but before that Fragment's onCreateView().
In this method, you can assign variables, get Intent extras, and anything else that doesn't involve the View hierarchy (i.e. non-graphical initialisations). This is because this method can be called when the Activity's onCreate() is not finished, and so trying to access the View hierarchy here may result in a crash.

onCreateView():

After the onCreate() is called (in the Fragment), the Fragment's onCreateView() is called. You can assign your View variables and do any graphical initialisations. You are expected to return a View to this method, and this is the main UI view, but if your Fragment does not use any layouts or graphics, you can return null.

onActivityCreated():

As the name states, this is called after the Activity's onCreate() has completed. It is called after onCreateView(), and is mainly used for final initialisations (for example, modifying UI elements).

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To sum up...
They are all called in the Fragment but are called at different times.
The onCreate() is called first, for doing any non-graphical initialisations. Next, you can assign and declare any View variables you want to use in onCreateView(). Afterwards, use onActivityCreated() to do any final initialisations you want to do once everything has completed.

轉載自此StackOverFlow