Ok, vielleicht war ich etwas zu hart in der Android-Dokumentation, weil sie einige nützliche Informationen enthält, aber leider ist nichts davon verlinkt setRetainInstance(). Von der Seite über Fragmente
Hinweis: Für jedes Fragment ist eine eindeutige Kennung erforderlich, mit der das System das Fragment wiederherstellen kann, wenn die Aktivität neu gestartet wird (und mit der Sie das Fragment erfassen können, um Transaktionen auszuführen, z. B. um es zu entfernen). Es gibt drei Möglichkeiten, eine ID für ein Fragment bereitzustellen:
- Geben Sie dem Attribut android: id eine eindeutige ID an.
- Geben Sie dem Attribut android: tag eine eindeutige Zeichenfolge an.
- Wenn Sie keine der beiden vorherigen angeben, verwendet das System die ID der Containeransicht.
Dies bedeutet , stark , dass , wenn Sie tun setContentView(R.layout.whatever)in Activity.onCreated()und dass das Layout ein Fragment mit enthält setRetainInstance(true), dann , wenn die Aktivität neu erstellt wird es wieder mit seinem ID oder Tag durchsucht werden.
Zweitens heißt es für Fragmente ohne Benutzeroberfläche
Um ein Fragment ohne Benutzeroberfläche hinzuzufügen, fügen Sie das Fragment aus der Aktivität hinzu, indem Sie add (Fragment, String) verwenden (und geben Sie eine eindeutige Zeichenfolge "tag" für das Fragment anstelle einer Ansichts-ID an). Dadurch wird das Fragment hinzugefügt. Da es jedoch keiner Ansicht im Aktivitätslayout zugeordnet ist, wird onCreateView () nicht aufgerufen. Sie müssen diese Methode also nicht implementieren.
Und die Dokumentation enthält einen Link zu einem sehr guten Beispiel, FragmentRetainInstance.javadas ich unten zur Vereinfachung wiedergegeben habe. Es macht genau das, was ich spekuliert habe, war die Antwort in meiner Frage ( if (...findFragmentByTag() == null) { ...).
Schließlich habe ich meine eigene Testaktivität erstellt, um genau zu sehen, welche Funktionen aufgerufen werden. Dies wird ausgegeben, wenn Sie im Hochformat beginnen und im Querformat drehen. Der Code ist unten.
(Dies wird etwas bearbeitet, um das Lesen zu erleichtern.)
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()
Beachten Sie, dass die Android-Dokumentation falsch ist: Das Fragment ohne Benutzeroberfläche wird zwar angerufen, kann onCreateView()jedoch kostenlos zurückgegeben werden null.
Quellcode für 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()");
}
}
}
Quellcode für FragmentRetainInstance.java(ab 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();
}
}
}
}