Compréhension plus poussée setRetainInstance (true)


109

Que se passe- t-il exactement lorsque vous appelez setRetainInstance(true)un Fragment? La documentation est pratiquement inexistante et cela semble être une fonction très importante. Plus précisément, je veux savoir dans quelle mesure cette séquence (que j'ai inventée) est vraie:

  1. L'utilisateur fait pivoter l'appareil.
  2. Le fragment est détaché de Activityet Fragment.onDetach()est appelé.
  3. L'activité est détruite; Activity.onDestroy()est appelé.
  4. L' Activityobjet java est supprimé (si possible, par le GC).
  5. Un nouvel Activityobjet java est créé; son constructeur, et onCreate()sont appelés.
  6. Dans Activity.onCreate()nous avons soit setContentView(...)qui définit une mise en page contenant un fragment, soit nous utilisons FragmentTransaction pour ajouter un fragment.
  7. Je ne suis vraiment pas sûr de cela, mais je suppose qu'android est assez intelligent pour trouver l'ancien fragment et appeler Fragment.onAttach() à le rattacher au nouveauActivity
  8. Le suivant (ou avant? Qui sait?) Activity.onResume()Est appelé.

Alors, est-ce exact? Android est-il suffisamment intelligent pour trouver l'ancien fragment, même si j'utilise explicitement FragmentTransaction.add(new MyFragment(), ...)la première fois? Et si oui, comment éviter d'ajouter un autre fragment onCreate()? Dois-je faire quelque chose comme ça?:

    if (getSupportFragmentManager().findFragmentByTag("foo") == null)
    {
        FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
        ft.add(new FooFragment(), "foo").commit();
    }

Réponses:


94

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

Remarque: chaque fragment nécessite un identifiant unique que le système peut utiliser pour restaurer le fragment si l'activité est redémarrée (et que vous pouvez utiliser pour capturer le fragment pour effectuer des transactions, comme le supprimer). Il existe trois façons de fournir un identifiant pour un fragment:

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

Cela implique fortement que si vous faites setContentView(R.layout.whatever)dans Activity.onCreated()et que la mise en page contient un fragment avecsetRetainInstance(true) , alors lorsque l'activité est recréée, elle sera à nouveau recherchée en utilisant son identifiant ou sa balise.

Deuxièmement, pour les fragments sans interface utilisateur, il indique

Pour ajouter un fragment sans interface utilisateur, ajoutez le fragment de l'activité à l'aide de add (Fragment, String) (en fournissant une chaîne unique "tag" pour le fragment, plutôt qu'un ID de vue). Cela ajoute le fragment, mais, comme il n'est pas associé à une vue dans la disposition d'activité, il ne reçoit pas d'appel à onCreateView (). Vous n'avez donc pas besoin d'implémenter cette méthode.

Et les documents renvoient à un très bon exemple - FragmentRetainInstance.javaque j'ai reproduit ci-dessous pour votre commodité. Il fait exactement ce que j'ai supposé était la réponse à ma question ( if (...findFragmentByTag() == null) { ...).

Enfin, j'ai créé ma propre activité de test pour voir exactement quelles fonctions sont appelées. Il génère cela, lorsque vous démarrez en portrait et que vous faites une rotation en paysage. Le code est ci-dessous.

(Ceci est modifié 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 de l' interface utilisateur-moins ne reçoit un appel , onCreateView()mais il est libre de revenir 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 pour FragmentRetainInstance.java(à partir de l'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();
            }
        }
    }
}

Pourriez-vous regarder ma question et me dire comment je mettrais en œuvre votre solution. Mon application fonctionne mais je souhaite supprimer android: configChanges = "orientation | keyboardHidden | screenSize" et cela empêchera l'application de conserver son écouteur de fragments après le changement de configuration. stackoverflow.com/questions/35941585/…
Luke Allison

44

setRetainInstance()in Fragmentclass est un remplacement intelligent pour onRetainCustomNonConfigurationInstance()of Activityclass, et plus encore.

Clairement indiqué dans la documentation .

Voici le journal de ce qui se passe (un fragment d'interface utilisateur ajouté à la demande, puis un changement de configuration):

Défaut setRetainInstance(false)

09-29 13:23:04.771: DEBUG/szipinf(4790): Initializing inflate state
09-29 13:23:04.801: INFO/TESTING - MYACTIVITY(4790): Instantiated - com.example.MyActivity@405196b0
09-29 13:23:04.851: DEBUG/dalvikvm(4790): GC_EXTERNAL_ALLOC freed 49K, 51% free 2686K/5379K, external 0K/0K, paused 45ms
09-29 13:23:04.881: INFO/TESTING - MYACTIVITY(4790): onCreate - com.example.MyActivity@405196b0
09-29 13:23:04.881: INFO/TESTING - MYACTIVITY(4790): onStart - com.example.MyActivity@405196b0
09-29 13:23:04.881: INFO/TESTING - MYACTIVITY(4790): onResume - com.example.MyActivity@405196b0
09-29 13:23:04.891: INFO/TESTING - MYACTIVITY(4790): onAttachedToWindow - com.example.MyActivity@405196b0
09-29 13:23:10.381: DEBUG/dalvikvm(4457): GC_EXPLICIT freed 8K, 51% free 2681K/5379K, external 0K/0K, paused 38ms
09-29 13:23:11.901: INFO/TESTING - MYFRAGMENT(4790): Instantiated - MyFragment{40530610}
09-29 13:23:11.911: INFO/TESTING - MYFRAGMENT(4790): onAttach - MyFragment{40530610 #0 MyFragment}
09-29 13:23:11.911: INFO/TESTING - MYACTIVITY(4790): onAttachFragment - com.example.MyActivity@405196b0
09-29 13:23:11.911: INFO/TESTING - MYFRAGMENT(4790): onCreate - MyFragment{40530610 #0 MyFragment}
09-29 13:23:11.911: INFO/TESTING - MYFRAGMENT(4790): onCreateView - MyFragment{40530610 #0 MyFragment}
09-29 13:23:11.921: INFO/TESTING - MYFRAGMENT(4790): onViewCreated - MyFragment{40530610 #0 MyFragment}
09-29 13:23:11.921: INFO/TESTING - MYFRAGMENT(4790): onActivityCreated - MyFragment{40530610 #0 MyFragment}
09-29 13:23:11.931: INFO/TESTING - MYFRAGMENT(4790): onStart - MyFragment{40530610 #0 MyFragment}
09-29 13:23:11.931: INFO/TESTING - MYFRAGMENT(4790): onResume - MyFragment{40530610 #0 MyFragment}
09-29 13:23:15.081: INFO/ActivityManager(1268): Config changed: { scale=1.0 imsi=404/45 loc=en_US touch=3 keys=1/1/2 nav=1/1 orien=2 layout=34 uiMode=17 seq=105 themeResource=null}
09-29 13:23:15.111: INFO/TESTING - MYACTIVITY(4790): onSaveInstanceState - com.example.MyActivity@405196b0
09-29 13:23:15.111: INFO/TESTING - MYFRAGMENT(4790): onPause - MyFragment{40530610 #0 MyFragment}
09-29 13:23:15.121: INFO/TESTING - MYACTIVITY(4790): onPause - com.example.MyActivity@405196b0
09-29 13:23:15.121: INFO/TESTING - MYFRAGMENT(4790): onStop - MyFragment{40530610 #0 MyFragment}
09-29 13:23:15.121: INFO/TESTING - MYACTIVITY(4790): onStop - com.example.MyActivity@405196b0
09-29 13:23:15.121: INFO/TESTING - MYACTIVITY(4790): onRetainCustomNonConfigurationInstance - com.example.MyActivity@405196b0
09-29 13:23:15.121: INFO/TESTING - MYFRAGMENT(4790): onDestroyView - MyFragment{40530610 #0 MyFragment}
09-29 13:23:15.121: INFO/TESTING - MYFRAGMENT(4790): onDestroy - MyFragment{40530610 #0 MyFragment}
09-29 13:23:15.121: INFO/TESTING - MYFRAGMENT(4790): onDetach - MyFragment{40530610 #0 MyFragment}
09-29 13:23:15.121: INFO/TESTING - MYACTIVITY(4790): onDestroy - com.example.MyActivity@405196b0
09-29 13:23:15.191: INFO/TESTING - MYACTIVITY(4790): onDetachedFromWindow - com.example.MyActivity@405196b0
09-29 13:23:15.201: INFO/TESTING - MYACTIVITY(4790): Instantiated - com.example.MyActivity@4053c438
09-29 13:23:15.201: INFO/TESTING - MYFRAGMENT(4790): Instantiated - MyFragment{4053cde0}
09-29 13:23:15.201: INFO/TESTING - MYFRAGMENT(4790): onAttach - MyFragment{4053cde0 #0 MyFragment}
09-29 13:23:15.201: INFO/TESTING - MYACTIVITY(4790): onAttachFragment - com.example.MyActivity@4053c438
09-29 13:23:15.201: INFO/TESTING - MYFRAGMENT(4790): onCreate - MyFragment{4053cde0 #0 MyFragment}
09-29 13:23:15.251: INFO/TESTING - MYACTIVITY(4790): onCreate - com.example.MyActivity@4053c438
09-29 13:23:15.251: INFO/TESTING - MYFRAGMENT(4790): onCreateView - MyFragment{4053cde0 #0 MyFragment}
09-29 13:23:15.261: INFO/TESTING - MYFRAGMENT(4790): onViewCreated - MyFragment{4053cde0 #0 MyFragment}
09-29 13:23:15.261: INFO/TESTING - MYFRAGMENT(4790): onActivityCreated - MyFragment{4053cde0 #0 MyFragment}
09-29 13:23:15.291: INFO/TESTING - MYFRAGMENT(4790): onStart - MyFragment{4053cde0 #0 MyFragment}
09-29 13:23:15.291: INFO/TESTING - MYACTIVITY(4790): onStart - com.example.MyActivity@4053c438
09-29 13:23:15.291: INFO/TESTING - MYACTIVITY(4790): onResume - com.example.MyActivity@4053c438
09-29 13:23:15.291: INFO/TESTING - MYFRAGMENT(4790): onResume - MyFragment{4053cde0 #0 MyFragment}
09-29 13:23:15.321: INFO/TESTING - MYACTIVITY(4790): onAttachedToWindow - com.example.MyActivity@4053c438

Ainsi, Fragment est recréé entièrement nouveau, et montré à nouveau, tout cela setRetainInstance(false)

Et maintenant avec setRetainInstance(true)

09-29 13:18:46.121: INFO/ActivityManager(1268): Starting: Intent { flg=0x10100000 cmp=com.example/.MyActivity } from pid 1268
09-29 13:18:46.141: INFO/TESTING - MYACTIVITY(4726): Instantiated - com.example.MyActivity@4056f2e0
09-29 13:18:46.161: INFO/TESTING - MYACTIVITY(4726): onCreate - com.example.MyActivity@4056f2e0
09-29 13:18:46.161: INFO/TESTING - MYACTIVITY(4726): onStart - com.example.MyActivity@4056f2e0
09-29 13:18:46.161: INFO/TESTING - MYACTIVITY(4726): onResume - com.example.MyActivity@4056f2e0
09-29 13:18:46.191: INFO/TESTING - MYACTIVITY(4726): onAttachedToWindow - com.example.MyActivity@4056f2e0
09-29 13:19:10.431: DEBUG/SntpClient(1268): request time failed: java.net.UnknownHostException: europe.pool.ntp.org
09-29 13:19:14.251: INFO/TESTING - MYFRAGMENT(4726): Instantiated - MyFragment{405288c0}
09-29 13:19:14.271: INFO/TESTING - MYFRAGMENT(4726): onAttach - MyFragment{405288c0 #0 MyFragment}
09-29 13:19:14.271: INFO/TESTING - MYACTIVITY(4726): onAttachFragment - com.example.MyActivity@4056f2e0
09-29 13:19:14.271: INFO/TESTING - MYFRAGMENT(4726): onCreate - MyFragment{405288c0 #0 MyFragment}
09-29 13:19:14.281: INFO/TESTING - MYFRAGMENT(4726): onCreateView - MyFragment{405288c0 #0 MyFragment}
09-29 13:19:14.281: INFO/TESTING - MYFRAGMENT(4726): onViewCreated - MyFragment{405288c0 #0 MyFragment}
09-29 13:19:14.281: INFO/TESTING - MYFRAGMENT(4726): onActivityCreated - MyFragment{405288c0 #0 MyFragment}
09-29 13:19:14.291: INFO/TESTING - MYFRAGMENT(4726): onStart - MyFragment{405288c0 #0 MyFragment}
09-29 13:19:14.291: INFO/TESTING - MYFRAGMENT(4726): onResume - MyFragment{405288c0 #0 MyFragment}
09-29 13:19:21.921: INFO/ActivityManager(1268): Config changed: { scale=1.0 imsi=404/45 loc=en_US touch=3 keys=1/1/2 nav=1/1 orien=2 layout=34 uiMode=17 seq=103 themeResource=null}
09-29 13:19:21.961: INFO/TESTING - MYACTIVITY(4726): onSaveInstanceState - com.example.MyActivity@4056f2e0
09-29 13:19:21.961: INFO/TESTING - MYFRAGMENT(4726): onPause - MyFragment{405288c0 #0 MyFragment}
09-29 13:19:21.961: INFO/TESTING - MYACTIVITY(4726): onPause - com.example.MyActivity@4056f2e0
09-29 13:19:21.961: INFO/TESTING - MYFRAGMENT(4726): onStop - MyFragment{405288c0 #0 MyFragment}
09-29 13:19:21.961: INFO/TESTING - MYACTIVITY(4726): onStop - com.example.MyActivity@4056f2e0
09-29 13:19:21.961: INFO/TESTING - MYACTIVITY(4726): onRetainCustomNonConfigurationInstance - com.example.MyActivity@4056f2e0
09-29 13:19:21.961: INFO/TESTING - MYFRAGMENT(4726): onDestroyView - MyFragment{405288c0 #0 MyFragment}
09-29 13:19:21.961: INFO/TESTING - MYFRAGMENT(4726): onDetach - MyFragment{405288c0 #0 MyFragment}
09-29 13:19:21.961: INFO/TESTING - MYACTIVITY(4726): onDestroy - com.example.MyActivity@4056f2e0
09-29 13:19:22.111: INFO/TESTING - MYACTIVITY(4726): onDetachedFromWindow - com.example.MyActivity@4056f2e0
09-29 13:19:22.111: INFO/TESTING - MYACTIVITY(4726): Instantiated - com.example.MyActivity@4054a0e8
09-29 13:19:22.111: INFO/TESTING - MYFRAGMENT(4726): onAttach - MyFragment{405288c0 #0 MyFragment}
09-29 13:19:22.111: INFO/TESTING - MYACTIVITY(4726): onAttachFragment - com.example.MyActivity@4054a0e8
09-29 13:19:22.131: INFO/TESTING - MYACTIVITY(4726): onCreate - com.example.MyActivity@4054a0e8
09-29 13:19:22.131: INFO/TESTING - MYFRAGMENT(4726): onCreateView - MyFragment{405288c0 #0 MyFragment}
09-29 13:19:22.131: INFO/TESTING - MYFRAGMENT(4726): onViewCreated - MyFragment{405288c0 #0 MyFragment}
09-29 13:19:22.131: INFO/TESTING - MYFRAGMENT(4726): onActivityCreated - MyFragment{405288c0 #0 MyFragment}
09-29 13:19:22.141: INFO/TESTING - MYFRAGMENT(4726): onStart - MyFragment{405288c0 #0 MyFragment}
09-29 13:19:22.141: INFO/TESTING - MYACTIVITY(4726): onStart - com.example.MyActivity@4054a0e8
09-29 13:19:22.141: INFO/TESTING - MYACTIVITY(4726): onResume - com.example.MyActivity@4054a0e8
09-29 13:19:22.141: INFO/TESTING - MYFRAGMENT(4726): onResume - MyFragment{405288c0 #0 MyFragment}
09-29 13:19:22.171: INFO/TESTING - MYACTIVITY(4726): onAttachedToWindow - com.example.MyActivity@4054a0e8
09-29 13:19:22.181: INFO/TESTING - MYFRAGMENT(4726): onPause - MyFragment{405288c0 #0 MyFragment}
09-29 13:19:22.181: INFO/TESTING - MYFRAGMENT(4726): onStop - MyFragment{405288c0 #0 MyFragment}
09-29 13:19:22.181: INFO/TESTING - MYFRAGMENT(4726): onDestroyView - MyFragment{405288c0 #0 MyFragment}
09-29 13:19:22.181: INFO/TESTING - MYFRAGMENT(4726): onDestroy - MyFragment{405288c0 #0 MyFragment}
09-29 13:19:22.181: INFO/TESTING - MYFRAGMENT(4726): onDetach - MyFragment{405288c0 #0 MyFragment}

Vous avez remarqué l'effet? L'instance de fragment (objet 405288c0) a été conservée, ce qui est bon. Mais l'instance conservée est très susceptible de contenir des ressources, des vues et des objets appartenant à des orientations précédentes, ce qui peut entraîner des fuites de mémoire.

Des précautions supplémentaires doivent être prises lorsque vous écrivez le code pour initier ce fragment: vous devez toujours rechercher une instance préexistante.

Morale de l'histoire: setRetainInstance()est mieux utilisée pour les fragments non visuels.


deux journaux me donnent la réponse. Premier journal créer une nouvelle instance à chaque fois (40530610,4053cde0), après setRetainInstance () une seule instance 405288c0
Ranjith Kumar

0

Ainsi, vous pouvez coder dans protected void onCreate (Bundle savedInstanceState) à la classe d'activité

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    // add code findViewById...etc
    .....
    // add your fragment in code, IT WILL BE NOT CHANGE
    if(savedInstanceState==null){
        FragmentA a_fragment = new FragmentA();
        FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
        fragmentTransaction.replace(R.id.your_layout_id, a_fragment);
        fragmentTransaction.addToBackStack(null);
        fragmentTransaction.commit();
    }

}

Au lieu de

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    // add code findViewById...etc
    .....
    // add your fragment and not check savedInstanceState IT WILL BE CHANGE
    FragmentA a_fragment = new FragmentA();
    FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
    fragmentTransaction.replace(R.id.your_layout_id, a_fragment);
    fragmentTransaction.addToBackStack(null);
    fragmentTransaction.commit();


}

Rappelles toi

public View onCreateView(...) {

 // Remember add this line
 setRetainInstance(true);

 return root;
 }
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