Ok, peut-être que j'ai été un peu trop sévère avec la documentation Android, parce qu'elle contient des informations utiles, mais malheureusement aucune de ces informations n'est liée à setRetainInstance() . De la page sur les fragments

Note: chaque fragment nécessite un identifiant unique que le système peut utiliser pour restaurer le fragment si l'activité est redémarré (et qui vous pouvez utiliser pour capturer le fragment d'effectuer des transactions, tels que le supprimer). Il y a trois façons de fournir un ID pour un fragment:

• fournit l'attribut android:id avec un ID unique.
• fournit l'attribut android:tag avec une chaîne unique.
• si vous ne fournissez aucun des deux précédents, le système utilise L'ID de la vue conteneur.

cela implique fortement que si vous faites setContentView(R.layout.whatever) dans Activity.onCreated() et cette mise en page contient un fragment avec setRetainInstance(true) , puis lorsque l'activité est recréée il sera recherché à nouveau en utilisant son id ou étiquette.

Deuxièmement, pour les fragments sans UI, il est écrit

pour ajouter un fragment sans UI, ajouter le fragment de l'activité en utilisant add(Fragment, String) (fournissant une chaîne unique " tag " pour le fragment, plutôt qu'un ID de vue). Cela ajoute le fragment, mais, parce que ce n'est pas associée à une vue dans la mise en page de l'activité, il ne recevez un appel à onCreateView(). Si vous n'avez pas besoin de la mettre en méthode.

et le lien docs à un très bon exemple - FragmentRetainInstance.java que j'ai reproduit ci-dessous pour votre commodité. Il fait exactement ce que j'ai spéculé était la réponse dans ma question ( if (...findFragmentByTag() == null) { ... ).

finalement, j'ai créé ma propre activité de test pour voir exactement quelles fonctions sont appelées. Il produit ceci, quand vous commencer en portrait et tourner vers le paysage. Le code est ci-dessous.

(ceci est édité un peu pour le rendre plus facile à lire.)

TestActivity@415a4a30: this()
TestActivity@415a4a30: onCreate()
TestActivity@415a4a30: Existing fragment not found.
TestFragment{41583008}: this() TestFragment{41583008}
TestFragment{41583008}: onAttach(TestActivity@415a4a30)
TestFragment{41583008}: onCreate()
TestFragment{41583008}: onCreateView()
TestFragment{41583008}: onActivityCreated()
TestActivity@415a4a30: onStart()
TestFragment{41583008}: onStart()
TestActivity@415a4a30: onResume()
TestFragment{41583008}: onResume()

<rotate device>

TestFragment{41583008}: onPause()
TestActivity@415a4a30: onPause()
TestFragment{41583008}: onStop()
TestActivity@415a4a30: onStop()
TestFragment{41583008}: onDestroyView()
TestFragment{41583008}: onDetach()
TestActivity@415a4a30: onDestroy()
TestActivity@415a3380: this()
TestFragment{41583008}: onAttach(TestActivity@415a3380)
TestActivity@415a3380: onCreate()
TestActivity@415a3380: Existing fragment found.
TestFragment{41583008}: onCreateView()
TestFragment{41583008}: onActivityCreated()
TestActivity@415a3380: onStart()
TestFragment{41583008}: onStart()
TestActivity@415a3380: onResume()
TestFragment{41583008}: onResume()

notez que la documentation Android est erronée: le fragment sans UI ne recevoir un appel à onCreateView() mais il est libre de retourner null .

code Source pour TestActivity / TestFragment

import android.app.Activity;
import android.app.Fragment;
import android.app.FragmentTransaction;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import com.concentriclivers.ss.R;

// An activity for understanding Android lifecycle events.
public class TestActivity extends Activity
{
    private static final String TAG = TestActivity.class.getSimpleName();

    public TestActivity()
    {
        super();
        Log.d(TAG, this + ": this()");
    }

    protected void finalize() throws Throwable
    {
        super.finalize();
        Log.d(TAG, this + ": finalize()");
    }

    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        Log.d(TAG, this + ": onCreate()");


        TextView tv = new TextView(this);
        tv.setText("Hello world");
        setContentView(tv);

        if (getFragmentManager().findFragmentByTag("test_fragment") == null)
        {
            Log.d(TAG, this + ": Existing fragment not found.");
            FragmentTransaction ft = getFragmentManager().beginTransaction();
            ft.add(new TestFragment(), "test_fragment").commit();
        }
        else
        {
            Log.d(TAG, this + ": Existing fragment found.");
        }
    }

    @Override
    public void onStart()
    {
        super.onStart();
        Log.d(TAG, this + ": onStart()");
    }

    @Override
    public void onResume()
    {
        super.onResume();
        Log.d(TAG, this + ": onResume()");
    }

    @Override
    public void onPause()
    {
        super.onPause();
        Log.d(TAG, this + ": onPause()");
    }

    @Override
    public void onStop()
    {
        super.onStop();
        Log.d(TAG, this + ": onStop()");
    }

    @Override
    public void onDestroy()
    {
        super.onDestroy();
        Log.d(TAG, this + ": onDestroy()");
    }




    public static class TestFragment extends Fragment
    {
        private static final String TAG = TestFragment.class.getSimpleName();

        public TestFragment()
        {
            super();
            Log.d(TAG,  this + ": this() " + this);
        }

        @Override
        public void onCreate(Bundle savedInstanceState)
        {
            super.onCreate(savedInstanceState);
            Log.d(TAG, this + ": onCreate()");
            setRetainInstance(true);
        }

        @Override
        public void onAttach(final Activity activity)
        {
            super.onAttach(activity);
            Log.d(TAG, this + ": onAttach(" + activity + ")");
        }

        @Override
        public void onActivityCreated(Bundle savedInstanceState)
        {
            super.onActivityCreated(savedInstanceState);
            Log.d(TAG, this + ": onActivityCreated()");
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
        {
            Log.d(TAG, this + ": onCreateView()");
            return null;
        }

        @Override
        public void onViewCreated(View view, Bundle savedInstanceState)
        {
            super.onViewCreated(view, savedInstanceState);
            Log.d(TAG, this + ": onViewCreated()");
        }

        @Override
        public void onDestroyView()
        {
            super.onDestroyView();
            Log.d(TAG, this + ": onDestroyView()");
        }

        @Override
        public void onDetach()
        {
            super.onDetach();
            Log.d(TAG, this + ": onDetach()");
        }

        @Override
        public void onStart()
        {
            super.onStart();
            Log.d(TAG, this + ": onStart()");
        }

        @Override
        public void onResume()
        {
            super.onResume();
            Log.d(TAG, this + ": onResume()");
        }

        @Override
        public void onPause()
        {
            super.onPause();
            Log.d(TAG, this + ": onPause()");
        }

        @Override
        public void onStop()
        {
            super.onStop();
            Log.d(TAG, this + ": onStop()");
        }

        @Override
        public void onDestroy()
        {
            super.onDestroy();
            Log.d(TAG, this + ": onDestroy()");
        }
    }

}

code Source FragmentRetainInstance.java (comme d'API 16):

/*
 * Copyright (C) 2010 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.example.android.apis.app;

import com.example.android.apis.R;

import android.app.Activity;
import android.app.Fragment;
import android.app.FragmentManager;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ProgressBar;

/**
 * This example shows how you can use a Fragment to easily propagate state
 * (such as threads) across activity instances when an activity needs to be
 * restarted due to, for example, a configuration change.  This is a lot
 * easier than using the raw Activity.onRetainNonConfiguratinInstance() API.
 */
public class FragmentRetainInstance extends Activity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // First time init, create the UI.
        if (savedInstanceState == null) {
            getFragmentManager().beginTransaction().add(android.R.id.content,
                    new UiFragment()).commit();
        }
    }

    /**
     * This is a fragment showing UI that will be updated from work done
     * in the retained fragment.
     */
    public static class UiFragment extends Fragment {
        RetainedFragment mWorkFragment;

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {
            View v = inflater.inflate(R.layout.fragment_retain_instance, container, false);

            // Watch for button clicks.
            Button button = (Button)v.findViewById(R.id.restart);
            button.setOnClickListener(new OnClickListener() {
                public void onClick(View v) {
                    mWorkFragment.restart();
                }
            });

            return v;
        }

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

            FragmentManager fm = getFragmentManager();

            // Check to see if we have retained the worker fragment.
            mWorkFragment = (RetainedFragment)fm.findFragmentByTag("work");

            // If not retained (or first time running), we need to create it.
            if (mWorkFragment == null) {
                mWorkFragment = new RetainedFragment();
                // Tell it who it is working with.
                mWorkFragment.setTargetFragment(this, 0);
                fm.beginTransaction().add(mWorkFragment, "work").commit();
            }
        }

    }

    /**
     * This is the Fragment implementation that will be retained across
     * activity instances.  It represents some ongoing work, here a thread
     * we have that sits around incrementing a progress indicator.
     */
    public static class RetainedFragment extends Fragment {
        ProgressBar mProgressBar;
        int mPosition;
        boolean mReady = false;
        boolean mQuiting = false;

        /**
         * This is the thread that will do our work.  It sits in a loop running
         * the progress up until it has reached the top, then stops and waits.
         */
        final Thread mThread = new Thread() {
            @Override
            public void run() {
                // We'll figure the real value out later.
                int max = 10000;

                // This thread runs almost forever.
                while (true) {

                    // Update our shared state with the UI.
                    synchronized (this) {
                        // Our thread is stopped if the UI is not ready
                        // or it has completed its work.
                        while (!mReady || mPosition >= max) {
                            if (mQuiting) {
                                return;
                            }
                            try {
                                wait();
                            } catch (InterruptedException e) {
                            }
                        }

                        // Now update the progress.  Note it is important that
                        // we touch the progress bar with the lock held, so it
                        // doesn't disappear on us.
                        mPosition++;
                        max = mProgressBar.getMax();
                        mProgressBar.setProgress(mPosition);
                    }

                    // Normally we would be doing some work, but put a kludge
                    // here to pretend like we are.
                    synchronized (this) {
                        try {
                            wait(50);
                        } catch (InterruptedException e) {
                        }
                    }
                }
            }
        };

        /**
         * Fragment initialization.  We way we want to be retained and
         * start our thread.
         */
        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);

            // Tell the framework to try to keep this fragment around
            // during a configuration change.
            setRetainInstance(true);

            // Start up the worker thread.
            mThread.start();
        }

        /**
         * This is called when the Fragment's Activity is ready to go, after
         * its content view has been installed; it is called both after
         * the initial fragment creation and after the fragment is re-attached
         * to a new activity.
         */
        @Override
        public void onActivityCreated(Bundle savedInstanceState) {
            super.onActivityCreated(savedInstanceState);

            // Retrieve the progress bar from the target's view hierarchy.
            mProgressBar = (ProgressBar)getTargetFragment().getView().findViewById(
                    R.id.progress_horizontal);

            // We are ready for our thread to go.
            synchronized (mThread) {
                mReady = true;
                mThread.notify();
            }
        }

        /**
         * This is called when the fragment is going away.  It is NOT called
         * when the fragment is being propagated between activity instances.
         */
        @Override
        public void onDestroy() {
            // Make the thread go away.
            synchronized (mThread) {
                mReady = false;
                mQuiting = true;
                mThread.notify();
            }

            super.onDestroy();
        }

        /**
         * This is called right before the fragment is detached from its
         * current activity instance.
         */
        @Override
        public void onDetach() {
            // This fragment is being detached from its activity.  We need
            // to make sure its thread is not going to touch any activity
            // state after returning from this function.
            synchronized (mThread) {
                mProgressBar = null;
                mReady = false;
                mThread.notify();
            }

            super.onDetach();
        }

        /**
         * API for our UI to restart the progress thread.
         */
        public void restart() {
            synchronized (mThread) {
                mPosition = 0;
                mThread.notify();
            }
        }
    }
}