Fragment onCreateView and onActivityCreated called twice

Question

I'm developing an app using Android 4.0 ICS and fragments.

Consider this modified example from the ICS 4.0.3 (API level 15) API's demo example app:

public class FragmentTabs extends Activity {

private static final String TAG = FragmentTabs.class.getSimpleName();

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

    final ActionBar bar = getActionBar();
    bar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
    bar.setDisplayOptions(0, ActionBar.DISPLAY_SHOW_TITLE);

    bar.addTab(bar.newTab()
            .setText("Simple")
            .setTabListener(new TabListener<SimpleFragment>(
                    this, "mysimple", SimpleFragment.class)));

    if (savedInstanceState != null) {
        bar.setSelectedNavigationItem(savedInstanceState.getInt("tab", 0));
        Log.d(TAG, "FragmentTabs.onCreate tab: " + savedInstanceState.getInt("tab"));
        Log.d(TAG, "FragmentTabs.onCreate number: " + savedInstanceState.getInt("number"));
    }

}

@Override
protected void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    outState.putInt("tab", getActionBar().getSelectedNavigationIndex());
}

public static class TabListener<T extends Fragment> implements ActionBar.TabListener {
    private final Activity mActivity;
    private final String mTag;
    private final Class<T> mClass;
    private final Bundle mArgs;
    private Fragment mFragment;

    public TabListener(Activity activity, String tag, Class<T> clz) {
        this(activity, tag, clz, null);
    }

    public TabListener(Activity activity, String tag, Class<T> clz, Bundle args) {
        mActivity = activity;
        mTag = tag;
        mClass = clz;
        mArgs = args;

        // Check to see if we already have a fragment for this tab, probably
        // from a previously saved state.  If so, deactivate it, because our
        // initial state is that a tab isn't shown.
        mFragment = mActivity.getFragmentManager().findFragmentByTag(mTag);
        if (mFragment != null && !mFragment.isDetached()) {
            Log.d(TAG, "constructor: detaching fragment " + mTag);
            FragmentTransaction ft = mActivity.getFragmentManager().beginTransaction();
            ft.detach(mFragment);
            ft.commit();
        }
    }

    public void onTabSelected(Tab tab, FragmentTransaction ft) {
        if (mFragment == null) {
            mFragment = Fragment.instantiate(mActivity, mClass.getName(), mArgs);
            Log.d(TAG, "onTabSelected adding fragment " + mTag);
            ft.add(android.R.id.content, mFragment, mTag);
        } else {
            Log.d(TAG, "onTabSelected attaching fragment " + mTag);
            ft.attach(mFragment);
        }
    }

    public void onTabUnselected(Tab tab, FragmentTransaction ft) {
        if (mFragment != null) {
            Log.d(TAG, "onTabUnselected detaching fragment " + mTag);
            ft.detach(mFragment);
        }
    }

    public void onTabReselected(Tab tab, FragmentTransaction ft) {
        Toast.makeText(mActivity, "Reselected!", Toast.LENGTH_SHORT).show();
    }
}

public static class SimpleFragment extends Fragment {
    TextView textView;
    int mNum;

    /**
     * When creating, retrieve this instance's number from its arguments.
     */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Log.d(FragmentTabs.TAG, "onCreate " + (savedInstanceState != null ? ("state " + savedInstanceState.getInt("number")) : "no state"));
        if(savedInstanceState != null) {
            mNum = savedInstanceState.getInt("number");
        } else {
            mNum = 25;
        }
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        Log.d(TAG, "onActivityCreated");
        if(savedInstanceState != null) {
            Log.d(TAG, "saved variable number: " + savedInstanceState.getInt("number"));
        }
        super.onActivityCreated(savedInstanceState);
    }

    @Override
    public void onSaveInstanceState(Bundle outState) {
        Log.d(TAG, "onSaveInstanceState saving: " + mNum);
        outState.putInt("number", mNum);
        super.onSaveInstanceState(outState);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        Log.d(FragmentTabs.TAG, "onCreateView " + (savedInstanceState != null ? ("state: " + savedInstanceState.getInt("number")) : "no state"));
        textView = new TextView(getActivity());
        textView.setText("Hello world: " + mNum);
        textView.setBackgroundDrawable(getResources().getDrawable(android.R.drawable.gallery_thumb));
        return textView;
    }
}

}

Here is the output retrieved from running this example and then rotating the phone:

06-11 11:31:42.559: D/FragmentTabs(10726): onTabSelected adding fragment mysimple
06-11 11:31:42.559: D/FragmentTabs(10726): onCreate no state
06-11 11:31:42.559: D/FragmentTabs(10726): onCreateView no state
06-11 11:31:42.567: D/FragmentTabs(10726): onActivityCreated
06-11 11:31:45.286: D/FragmentTabs(10726): onSaveInstanceState saving: 25
06-11 11:31:45.325: D/FragmentTabs(10726): onCreate state 25
06-11 11:31:45.340: D/FragmentTabs(10726): constructor: detaching fragment mysimple
06-11 11:31:45.340: D/FragmentTabs(10726): onTabSelected attaching fragment mysimple
06-11 11:31:45.348: D/FragmentTabs(10726): FragmentTabs.onCreate tab: 0
06-11 11:31:45.348: D/FragmentTabs(10726): FragmentTabs.onCreate number: 0
06-11 11:31:45.348: D/FragmentTabs(10726): onCreateView state: 25
06-11 11:31:45.348: D/FragmentTabs(10726): onActivityCreated
06-11 11:31:45.348: D/FragmentTabs(10726): saved variable number: 25
06-11 11:31:45.348: D/FragmentTabs(10726): onCreateView no state
06-11 11:31:45.348: D/FragmentTabs(10726): onActivityCreated

My question is, why is the onCreateView and onActivityCreated called twice? The first time with a Bundle with the saved state and the second time with a null savedInstanceState?

This is causing problems with retaining the state of the fragment on rotation.

Selfcontent

I think this question can be related to https://mcmap.net/q/56337/-android-fragment-lifecycle-over-orientation-changes – Atalante

Answer 1

Ok, Here's what I found out.

What I didn't understand is that all fragments that are attached to an activity when a config change happens (phone rotates) are recreated and added back to the activity. (which makes sense)

What was happening in the TabListener constructor was the tab was detached if it was found and attached to the activity. See below:

mFragment = mActivity.getFragmentManager().findFragmentByTag(mTag);
    if (mFragment != null && !mFragment.isDetached()) {
        Log.d(TAG, "constructor: detaching fragment " + mTag);
        FragmentTransaction ft = mActivity.getFragmentManager().beginTransaction();
        ft.detach(mFragment);
        ft.commit();
    }

Later in the activity onCreate the previously selected tab was selected from the saved instance state. See below:

if (savedInstanceState != null) {
    bar.setSelectedNavigationItem(savedInstanceState.getInt("tab", 0));
    Log.d(TAG, "FragmentTabs.onCreate tab: " + savedInstanceState.getInt("tab"));
    Log.d(TAG, "FragmentTabs.onCreate number: " + savedInstanceState.getInt("number"));
}

When the tab was selected it would be reattached in the onTabSelected callback.

public void onTabSelected(Tab tab, FragmentTransaction ft) {
    if (mFragment == null) {
        mFragment = Fragment.instantiate(mActivity, mClass.getName(), mArgs);
        Log.d(TAG, "onTabSelected adding fragment " + mTag);
        ft.add(android.R.id.content, mFragment, mTag);
    } else {
        Log.d(TAG, "onTabSelected attaching fragment " + mTag);
        ft.attach(mFragment);
    }
}

The fragment being attached is the second call to the onCreateView and onActivityCreated methods. (The first being when the system is recreating the acitivity and all attached fragments) The first time the onSavedInstanceState Bundle would have saved data but not the second time.

The solution is to not detach the fragment in the TabListener constructor, just leave it attached. (You still need to find it in the FragmentManager by it's tag) Also, in the onTabSelected method I check to see if the fragment is detached before I attach it. Something like this:

public void onTabSelected(Tab tab, FragmentTransaction ft) {
            if (mFragment == null) {
                mFragment = Fragment.instantiate(mActivity, mClass.getName(), mArgs);
                Log.d(TAG, "onTabSelected adding fragment " + mTag);
                ft.add(android.R.id.content, mFragment, mTag);
            } else {

                if(mFragment.isDetached()) {
                    Log.d(TAG, "onTabSelected attaching fragment " + mTag);
                    ft.attach(mFragment);
                } else {
                    Log.d(TAG, "onTabSelected fragment already attached " + mTag);
                }
            }
        }

Selfcontent

The mentioned "not to detach the fragment in the TabListener constructor" solutions causes the tab fragments to overlap each other. I can see the other fragments contents. It doesn't work for me. – Doubletongue

@flock.dux I'm not sure what you mean by overlapp each other. Android takes care of how they are layed out so, we just specify attach or detach. There must be more going on. Maybe if you ask a new question with example code we can figure out what's going on for you. – Selfcontent

I had the same problem (multiple fragment constructor calls from Android). Your finding solves my problem: What I didn't understand is that all fragments that are attached to an activity when a config change happens (phone rotates) are recreated and added back to the activity. (which makes sense) – Upthrow

Answer 2

I was scratching my head about this for a while too, and since Dave's explanation is a little hard to understand I'll post my (apparently working) code:

private class TabListener<T extends Fragment> implements ActionBar.TabListener {
    private Fragment mFragment;
    private Activity mActivity;
    private final String mTag;
    private final Class<T> mClass;

    public TabListener(Activity activity, String tag, Class<T> clz) {
        mActivity = activity;
        mTag = tag;
        mClass = clz;
        mFragment=mActivity.getFragmentManager().findFragmentByTag(mTag);
    }

    public void onTabSelected(Tab tab, FragmentTransaction ft) {
        if (mFragment == null) {
            mFragment = Fragment.instantiate(mActivity, mClass.getName());
            ft.replace(android.R.id.content, mFragment, mTag);
        } else {
            if (mFragment.isDetached()) {
                ft.attach(mFragment);
            }
        }
    }

    public void onTabUnselected(Tab tab, FragmentTransaction ft) {
        if (mFragment != null) {
            ft.detach(mFragment);
        }
    }

    public void onTabReselected(Tab tab, FragmentTransaction ft) {
    }
}

As you can see it's pretty much like the Android sample, apart from not detaching in the constructor, and using replace instead of add.

After much headscratching and trial-and-error I found that finding the fragment in the constructor seems to make the double onCreateView problem magically go away (I assume it just ends up being null for onTabSelected when called through the ActionBar.setSelectedNavigationItem() path when saving/restoring state).

Drugstore

Works perfectly well! You saved my night's sleep! Thank you :) – Indo

you can also use fragment.getClass().getName() if you want to remove the class variable and remove a parameter from the call – Mulch

Works perfectly with "previous ref. TabListener" Android sample - tnx. Newest Android "TabListener ref. sample" [as on 4 ix 2013] is really, really wrong. – Crackerjack

where is the ft.commit() method call ?? – Daytoday

Nice workaround. But why used replace instead of add. I don't see any significance difference. – Hyperpyrexia

This worked for me. In my case I only needed to use replace instead of add Not sure why, but it worked, although replace behaves different than add if you look at the documentation. – Equivocal

In my case the culprit was using of tag of a wrong fragment. – Dodiedodo

@MuhammadBabar, see #23249289. If you use add instead of replace and rotate screen, you will have many fragments' onCreateView(). – Desdamonna

also scratching, because a variable was reset to initial value in the "second" instantiating of the fragment. I did the mistake of setting (e.g.) int i = 0; in the declaration, and even if this i variable got another value during .onCreateView, etc, it was always finally reset to 0. Note that it is ONLY the declarations in the fragment that are regenerated in the second instantiation, the fragment code is not running after that. I.E. : Set values in .onCreateView or later, and the problem is solved. In case it help others. – Cuttlebone

Answer 3

I have had the same problem with a simple Activity carrying only one fragment (which would get replaced sometimes). I then realized I use onSaveInstanceState only in the fragment (and onCreateView to check for savedInstanceState), not in the activity.

On device turn the activity containing the fragments gets restarted and onCreated is called. There I did attach the required fragment (which is correct on the first start).

On the device turn Android first re-created the fragment that was visible and then called onCreate of the containing activity where my fragment was attached, thus replacing the original visible one.

To avoid that I simply changed my activity to check for savedInstanceState:

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

if (savedInstanceState != null) {
/**making sure you are not attaching the fragments again as they have 
 been 
 *already added
 **/
 return; 
 }
 else{
  // following code to attach fragment initially
 }

 }

I did not even Overwrite onSaveInstanceState of the activity.

Firebrick

Thank you. It helped me with AppCompatActivity + PreferenceFragmentCompat and crashing while showing dialogs in preference fragment after orientation change, as fragment manager was null on second fragment creation. – Caracal

Answer 4

The two upvoted answers here show solutions for an Activity with navigation mode NAVIGATION_MODE_TABS, but I had the same issue with a NAVIGATION_MODE_LIST. It caused my Fragments to inexplicably lose their state when the screen orientation changed, which was really annoying. Thankfully, due to their helpful code I managed to figure it out.

Basically, when using a list navigation, onNavigationItemSelected() is automatically called when your activity is created/re-created, whether you like it or not. To prevent your Fragment's onCreateView() from being called twice, this initial automatic call to onNavigationItemSelected() should check whether the Fragment is already in existence inside your Activity. If it is, return immediately, because there is nothing to do; if it isn't, then simply construct the Fragment and add it to the Activity like you normally would. Performing this check prevents your Fragment from needlessly being created again, which is what causes onCreateView() to be called twice!

See my onNavigationItemSelected() implementation below.

public class MyActivity extends FragmentActivity implements ActionBar.OnNavigationListener
{
    private static final String STATE_SELECTED_NAVIGATION_ITEM = "selected_navigation_item";

    private boolean mIsUserInitiatedNavItemSelection;

    // ... constructor code, etc.

    @Override
    public void onRestoreInstanceState(Bundle savedInstanceState)
    {
        super.onRestoreInstanceState(savedInstanceState);

        if (savedInstanceState.containsKey(STATE_SELECTED_NAVIGATION_ITEM))
        {
            getActionBar().setSelectedNavigationItem(savedInstanceState.getInt(STATE_SELECTED_NAVIGATION_ITEM));
        }
    }

    @Override
    public void onSaveInstanceState(Bundle outState)
    {
        outState.putInt(STATE_SELECTED_NAVIGATION_ITEM, getActionBar().getSelectedNavigationIndex());

        super.onSaveInstanceState(outState);
    }

    @Override
    public boolean onNavigationItemSelected(int position, long id)
    {    
        Fragment fragment;
        switch (position)
        {
            // ... choose and construct fragment here
        }

        // is this the automatic (non-user initiated) call to onNavigationItemSelected()
        // that occurs when the activity is created/re-created?
        if (!mIsUserInitiatedNavItemSelection)
        {
            // all subsequent calls to onNavigationItemSelected() won't be automatic
            mIsUserInitiatedNavItemSelection = true;

            // has the same fragment already replaced the container and assumed its id?
            Fragment existingFragment = getSupportFragmentManager().findFragmentById(R.id.container);
            if (existingFragment != null && existingFragment.getClass().equals(fragment.getClass()))
            {
                return true; //nothing to do, because the fragment is already there 
            }
        }

        getSupportFragmentManager().beginTransaction().replace(R.id.container, fragment).commit();
        return true;
    }
}

I borrowed inspiration for this solution from here.

Cenacle

This solution works for my similar problem with a navigation drawer. I find existing fragment by ID and check if it has the same class as the new fragment before recreating it. – Sectional

Answer 5

It looks to me like it's because you are instantiating your TabListener every time... so the system is recreating your fragment from the savedInstanceState and then you are doing it again in your onCreate.

You should wrap that in a if(savedInstanceState == null) so it only fires if there is no savedInstanceState.

Haemoid

I don't think that's correct. When i wrap my addTab code in the if block, the fragment is attached to the activity but there are no tabs. It appears you have to add the tabs every time in the onCreate method. I'll continue looking into this and post more as I understand better. – Selfcontent