Fragment.onCreate（）和Activity.onCreate（）之间的关系

Question

Dear fellow developers,

The relationship between a Fragment's onCreate() method and that of an Activity is not yet crystal clear to me. I'm attaching a Fragment to an Activity like this.

//happens in the Activity:
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState);
    FragmentManager fragMan = this.getSupportFragmentManager();
    Fragment dataModelFragment = fragMan.findFragmentByTag("data_model");
    if (dataModelFragment == null) {
        dataModelFragment = new DataModelFragment();
        fragMan.beginTransaction().add(dataModelFragment,"data_model").commit();
    }
    System.out.println("Executing Activity.onCreate()");
}

My Fragment's onCreate() has a Sysout.println() for testing purposes to see when exactly it executes. What makes me wonder is: why does the Activity's onCreate finish execution first, before even the Fragment's onCreate() is called? What happens is that the Sysout.println shown in the above code actually executes BEFORE the other Sysout.println, which is in the onCreate() of my Fragment. I would expect the Fragment's onCreate() to be executed before I add it to the Activity via the fragment transaction. Is it the way it is supposed to work? Or is the problem what I read in the docs that the commit() method does not execute immediately but places the fragment transaction only in the queue?

What I would like to achieve is this:

• I'm using a singleton instance of a Fragment as a data model to be retained across activity lifecycles.
• I'd like to add this fragment to the activity, then let this fragment perform its initialization (creating a database connection and loading the data into its data members)
• Finally this data from the fragment should be used with AdapterViews in the Activity's View.

So the three steps: initialize fragment with data, attach fragment to activity, create adapters in the activity from the fragment's data. My question: in which methods should these events occur to ensure the proper order of execution?

Many thanks!

Answer 1

From the Android FragmentTransaction.Commit() docs :

Schedules a commit of this transaction. The commit does not happen immediately; it will be scheduled as work on the main thread to be done the next time that thread is ready.

If you want your transaction to be processed immediately call FragmentManager.ExecutePendingTransactions() from your UI thread.