当您在setRetainInstance(true)上致电Fragment时，完全会发生什么？文档几乎不存在，这似乎是一个非常重要的功能。具体来说，我想知道这个序列（我编造的）有多少是真的：
- 用户旋转设备。
- 该片段与
Activity分离，并且Fragment.onDetach()被调用。- 活动被破坏;
Activity.onDestroy()被称为。{/ li>- 删除
Activityjava对象（如果可能，由GC删除）。- 创建一个新的
Activityjava对象;它的构造函数和onCreate()被调用。- 在
Activity.onCreate()我们要么setContentView(...)设置包含片段的布局，要么我们使用FragmentTransaction添加片段。- 我真的不确定这一点，但我认为android很聪明，可以找到旧片段，并调用
Fragment.onAttach()来 将其重新附加到新的Activity- 下一个（或之前？谁知道？）
Activity.onResume()被调用。
那是对的吗？即使我第一次明确使用FragmentTransaction.add(new MyFragment(), ...)，Android是否足够智能才能找到旧片段？如果是这样，我如何避免在onCreate()中添加另一个片段？我需要做这样的事情吗？：
if (getSupportFragmentManager().findFragmentByTag("foo") == null)
{
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
ft.add(new FooFragment(), "foo").commit();
}
答案 0 :(得分：90)
好吧，也许我对Android文档稍微过于苛刻，因为它确实有一些有用的信息，但很遗憾没有一个链接来自setRetainInstance()。来自the page about fragments
注意：每个片段都需要系统可以使用的唯一标识符 如果重新启动活动，则用于恢复片段（以及 您可以使用捕获片段来执行事务，例如 去掉它）。有三种方法可以为片段提供ID：
- 使用唯一ID提供android：id属性。
- 使用唯一字符串提供android：tag属性。
- 如果您不提供前两个，系统将使用容器视图的ID。
这强烈暗示如果您在setContentView(R.layout.whatever)中执行Activity.onCreated()并且该布局包含带有setRetainInstance(true)的片段，那么当重新创建活动时，将使用其ID再次搜索它标签
其次，对于无UI片段，它表示
要添加没有UI的片段，请从活动中添加片段 使用add（Fragment，String）（为。提供唯一的字符串“tag”） 片段，而不是视图ID）。这会添加片段，但是，因为 它与活动布局中的视图无关，但却没有 接到onCreateView（）的调用。所以你不需要实现它 方法
文档链接到一个非常好的示例 - FragmentRetainInstance.java我为了您的方便而在下面重现了这些示例。它完全符合我推测的问题（if (...findFragmentByTag() == null) { ...）中的答案。
最后，我创建了自己的测试活动，以确切了解调用哪些函数。当您以纵向开始并旋转到横向时，它会输出此信息。代码如下。
（稍微编辑一下以便于阅读。）
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()
请注意，Android文档错误：无UI片段 会接到onCreateView()的来电，但可以免费返回null。
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()");
}
}
}
FragmentRetainInstance.java的源代码（自API 16起）：/*
* 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();
}
}
}
}
答案 1 :(得分：41)
setRetainInstance()课程中的 Fragment是onRetainCustomNonConfigurationInstance() Activity课程的明智替代品，等等。
明确指出in the documentation。
这是发生了什么的日志（按需添加UI片段，然后是配置更改）：
默认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
因此，Fragment会重新全新显示，并在setRetainInstance(false)
现在使用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}
注意到效果？片段实例（对象405288c0）被保留，这是好的。但是保留的实例很可能保存属于先前方向的资源和视图以及对象，这可能导致内存泄漏。
在编写代码以启动此片段时，必须进一步注意：您必须始终检查预先存在的实例。
故事的道德：setRetainInstance()最适合用于非视觉片段。
答案 2 :(得分：0)
因此您可以在活动类的onCreate（Bundle savedInstanceState）受保护的void中进行编码
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();
}
}
代替
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();
}
记住
public View onCreateView(...) {
// Remember add this line
setRetainInstance(true);
return root;
}