CODEWITHSUNDEEP
androidandroid-lifecycle
user3148156
user3148156

Reputation: 178

Do the initial callbacks of a fragment get called before or after Activity onStart()?

https://github.com/xxv/android-lifecycle shows that fragment onAttach, onCreate, on CreateView, and onActivityCreated are invoked prior to activity onStart. However, I tried logging this:

   public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        Log.e("TRACE", "MainActivity onCreate");
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Fragment firstFragment = FirstFragment.newInstance();
        getSupportFragmentManager().beginTransaction().replace(R.id.content, firstFragment).commit();
    }

    @Override
    public void onStart() {
        Log.e("TRACE", "MainActivity onStart");
        super.onStart();
    }

FirstFragment looks like this:

public class FirstFragment extends Fragment {

    public FirstFragment() {
        // Required empty public constructor
    }

    public static FirstFragment newInstance() {
        FirstFragment fragment = new FirstFragment();
        return fragment;
    }

    @Override
    public void onAttach(Context context) {
        Log.d("TRACE", "FirstFragment onAttach");
        super.onAttach(context);
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        Log.d("TRACE", "FirstFragment onCreate");
        super.onCreate(savedInstanceState);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        Log.d("TRACE", "FirstFragment onCreateView");
        return inflater.inflate(R.layout.fragment_first, container, false);
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        Log.d("TRACE", "FirstFragment onActivityCreated");
        super.onActivityCreated(savedInstanceState);
    }

And it printed this:

  1. MainActivity onCreate
  2. MainActivity onStart
  3. FirstFragment onAttach
  4. FirstFragment onCreate
  5. FirstFragment onCreateView
  6. FirstFragment onActivityCreated
  7. MainActivity onResume

Upvotes: 0

Views: 589

Answers (1)

Ben P.
Ben P.

Reputation: 54194

It depends on how the Fragment is added to the Activity.

There are two common ways to add a fragment to an activity: via a <fragment> tag in XML or via a FragmentTransaction executed in Java.

If, instead of providing an R.id.content view and using a FragmentTransaction, you create your FirstFragment by using an activity layout like this one:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <fragment
        android:id="@+id/content"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        class="com.example.stackoverflow.FirstFragment"/>

</LinearLayout>

You'll see this in the logs:

E/TRACE   ( 6094): MainActivity onCreate
D/TRACE   ( 6094): FirstFragment onAttach
D/TRACE   ( 6094): FirstFragment onCreate
D/TRACE   ( 6094): FirstFragment onCreateView
E/TRACE   ( 6094): MainActivity onStart
D/TRACE   ( 6094): FirstFragment onActivityCreated
E/TRACE   ( 6094): MainActivity onResume

As for why you're seeing the messages in the order you see them when using a FragmentTransaction, it comes down to the fact that the transaction is asynchronous; there's no guarantee that it will be executed as soon as you call commit(). In your case, the system doesn't actually get around to executing it until after your activity's onStart().

Upvotes: 1

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