Android Fragment lifecycle over orientation change

Question

Using the compatibility package to target 2.2 using Fragments.

After recoding an activity to use fragments in an app I could not get the orientation changes/state management working so I've created a small test app with a single FragmentActivity and a single Fragment.

The logs from the orientation changes are weird, with multiple calls to the fragments OnCreateView.

I'm obviously missing something - like detatching the fragment and reattaching it rather than creating a new instance, but I can't see any documentation which would indicate where I'm going wrong.

Can anyone shed some light on what I'm doing wrong here please. Thanks

The log is as follows after orientation changes.

Initial creation
12-04 11:57:15.808: D/FragmentTest.FragmentTestActivity(3143): onCreate
12-04 11:57:15.945: D/FragmentTest.FragmentOne(3143): OnCreateView
12-04 11:57:16.081: D/FragmentTest.FragmentOne(3143): OnCreateView->SavedInstanceState null


Orientation Change 1
12-04 11:57:39.031: D/FragmentTest.FragmentOne(3143): onSaveInstanceState
12-04 11:57:39.031: D/FragmentTest.FragmentTestActivity(3143): onCreate
12-04 11:57:39.031: D/FragmentTest.FragmentOne(3143): OnCreateView
12-04 11:57:39.031: D/FragmentTest.FragmentOne(3143): OnCreateView->SavedInstanceState not null
12-04 11:57:39.031: D/FragmentTest.FragmentOne(3143): OnCreateView
12-04 11:57:39.167: D/FragmentTest.FragmentOne(3143): OnCreateView->SavedInstanceState null


Orientation Change 2
12-04 11:58:32.162: D/FragmentTest.FragmentOne(3143): onSaveInstanceState
12-04 11:58:32.162: D/FragmentTest.FragmentOne(3143): onSaveInstanceState
12-04 11:58:32.361: D/FragmentTest.FragmentTestActivity(3143): onCreate
12-04 11:58:32.361: D/FragmentTest.FragmentOne(3143): OnCreateView
12-04 11:58:32.361: D/FragmentTest.FragmentOne(3143): OnCreateView->SavedInstanceState not null
12-04 11:58:32.361: D/FragmentTest.FragmentOne(3143): OnCreateView
12-04 11:58:32.361: D/FragmentTest.FragmentOne(3143): OnCreateView->SavedInstanceState not null
12-04 11:58:32.498: D/FragmentTest.FragmentOne(3143): OnCreateView
12-04 11:58:32.498: D/FragmentTest.FragmentOne(3143): OnCreateView->SavedInstanceState null

Main Activity (FragmentActivity)

public class FragmentTestActivity extends FragmentActivity {
/** Called when the activity is first created. */

private static final String TAG = "FragmentTest.FragmentTestActivity";


FragmentManager mFragmentManager;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    Log.d(TAG, "onCreate");

    mFragmentManager = getSupportFragmentManager();
    FragmentTransaction fragmentTransaction = mFragmentManager.beginTransaction();

    FragmentOne fragment = new FragmentOne();

    fragmentTransaction.add(R.id.fragment_container, fragment);
    fragmentTransaction.commit();
}

And the fragment

public class FragmentOne extends Fragment {

private static final String TAG = "FragmentTest.FragmentOne";

EditText mEditText;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {

    Log.d(TAG, "OnCreateView");

    View v = inflater.inflate(R.layout.fragmentonelayout, container, false);

    // Retrieve the text editor, and restore the last saved state if needed.
    mEditText = (EditText)v.findViewById(R.id.editText1);

    if (savedInstanceState != null) {

        Log.d(TAG, "OnCreateView->SavedInstanceState not null");

        mEditText.setText(savedInstanceState.getCharSequence("text"));
    }
    else {
        Log.d(TAG,"OnCreateView->SavedInstanceState null");
    }
    return v;
}

@Override
public void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);

    Log.d(TAG, "FragmentOne.onSaveInstanceState");

    // Remember the current text, to restore if we later restart.
    outState.putCharSequence("text", mEditText.getText());
}

Manifest

<uses-sdk android:minSdkVersion="8" />

<application
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name" >
    <activity
        android:label="@string/app_name"
        android:name=".activities.FragmentTestActivity" 
        android:configChanges="orientation">
        <intent-filter >
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
</application>

Answer 1

You're layering your Fragments one on top of the other.

When a config change occurs the old Fragment adds itself to the new Activity when it's recreated. This is a massive pain in the rear most of the time.

You can stop errors occurring by using the same Fragment rather than recreating a new one. Simply add this code:

if (savedInstanceState == null) {
    // only create fragment if activity is started for the first time
    mFragmentManager = getSupportFragmentManager();
    FragmentTransaction fragmentTransaction = mFragmentManager.beginTransaction();

    FragmentOne fragment = new FragmentOne();

    fragmentTransaction.add(R.id.fragment_container, fragment);
    fragmentTransaction.commit();
} else {        
    // do nothing - fragment is recreated automatically
}

Be warned though: problems will occur if you try and access Activity Views from inside the Fragment as the lifecycles will subtly change. (Getting Views from a parent Activity from a Fragment isn't easy).

Answer 2

To cite this book, "to ensure a consistent user experience, Android persists the Fragment layout and associated back stack when an Activity is restarted due to a configuration change." (p. 124)

And the way to approach that is to first check if the Fragment back stack has already been populated, and create the new fragment instance only if it hasn't:

@Override
public void onCreate(Bundle savedInstanceState) {

        ...    

    FragmentOne fragment = (FragmentOne) mFragmentManager.findFragmentById(R.id.fragment_container); 

    if (fragment == null) {
        FragmentTransaction fragmentTransaction = mFragmentManager.beginTransaction();
        fragmentTransaction.add(R.id.fragment_container, new FragmentOne());
        fragmentTransaction.commit();
    }
}

Answer 3

The onCreate() method of your activity is called after the orientation change as you have seen. So, do not execute the FragmentTransaction that adds the Fragment after the orientation change in your activity.

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    if (savedInstanceState==null) {
        //do your stuff
    }
}

The Fragments should and must be unchanged.

Answer 4

You can @Override the FragmentActivity using onSaveInstanceState(). Please be sure to not call the super.onSaveInstanceState() in the method.

Answer 5

We should always try to prevent nullpointer exception , so we have to check first in saveinstance method for bundle information. for brief explaination to check this blog link

public static class DetailsActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        if (getResources().getConfiguration().orientation
            == Configuration.ORIENTATION_LANDSCAPE) {
            // If the screen is now in landscape mode, we can show the
            // dialog in-line with the list so we don't need this activity.
            finish();
            return;
        }

        if (savedInstanceState == null) {
            // During initial setup, plug in the details fragment.
            DetailsFragment details = new DetailsFragment();
            details.setArguments(getIntent().getExtras());
            getFragmentManager().beginTransaction().add(android.R.id.content, details).commit();
        }
    } 
}

Answer 6

On configuration change, the framework will create a new instance of the fragment for you and add it to the activity. So instead of this:

FragmentOne fragment = new FragmentOne();

fragmentTransaction.add(R.id.fragment_container, fragment);

do this:

if (mFragmentManager.findFragmentByTag(FRAG1_TAG) == null) {
    FragmentOne fragment = new FragmentOne();

    fragmentTransaction.add(R.id.fragment_container, fragment, FRAG1_TAG);
}

Please note that the framework adds a new instance of FragmentOne on orientation change unless you call setRetainInstance(true), in which case it will add the old instance of FragmentOne.