ViewPager 中的片段在 getView() 中返回 null
Posted
技术标签:
【中文标题】ViewPager 中的片段在 getView() 中返回 null【英文标题】：Fragment inside ViewPager returning null in getView() 【发布时间】：2013-10-07 02:33:49 【问题描述】：在我的应用程序中，我有一个 ViewPager，在该 ViewPager 中大约有 17 个片段。我已经为纵向和横向设计了布局。
当我旋转屏幕时，getView() 方法返回一个空对象，不知道为什么会这样，我使用了setRetainInstance(true)，但还是一样，我使用PagerStateFragmentAdapter 作为我的适配器实施。
为什么会发生这种情况？
提前谢谢你。
编辑
MainActivity
public class MainActivity extends FragmentActivity implements ViewPagerController
public static final String READ_TYPE = "Read_type";
private static final String TAG = MainActivity.class.getSimpleName();
private int mReadType;
private ViewPager mBookPager;
@Override
public void goToNextPage()
// TODO Auto-generated method stub
int currentPage = mBookPager.getCurrentItem();
if(currentPage+1 < mBookPager.getAdapter().getCount())
FragmentPagerAdapter adapter = (FragmentPagerAdapter)mBookPager.getAdapter();
BookPageFragment bookPage = (BookPageFragment)adapter.getItem(currentPage);
bookPage.setCurrentPage(false);
bookPage = (BookPageFragment)adapter.getItem(currentPage+1);
bookPage.setCurrentPage(true);
mBookPager.setCurrentItem(currentPage+1, true);
@Override
public void goToPreviousPage()
// TODO Auto-generated method stub
int currentPage = mBookPager.getCurrentItem();
if(currentPage >= 0)
mBookPager.setCurrentItem(currentPage-1,true);
@Override
public void onBackPressed()
// TODO Auto-generated method stub
finish();
overridePendingTransition(R.anim.anim_move_to_right,R.anim.anim_from_left_to_right);
@Override
protected void onDestroy()
// TODO Auto-generated method stub
Log.i(TAG,"onDestroy");
mBookPager.removeAllViews();
mBookPager = null;
super.onDestroy();
@Override
protected void onCreate(Bundle arg0)
// TODO Auto-generated method stub
super.onCreate(arg0);
setContentView(R.layout.main_layout);
overridePendingTransition(R.anim.anim_from_right_to_left, R.anim.anim_move_to_left);
initReadType();
mBookPager = (ViewPager)findViewById(R.id.mainLayout_mainViewPager);
initViewPager();
private void initReadType()
mReadType = getIntent().getIntExtra(READ_TYPE, -1);
private void initViewPager()
BookPagerAdapter mPagerAdapter = new BookPagerAdapter(getSupportFragmentManager(),mReadType);
((BookPageFragment)mPagerAdapter.getItem(0)).setCurrentPage(true);
mBookPager.setAdapter(mPagerAdapter);
mBookPager.setOnPageChangeListener(mOnPageChangeListener);
private OnPageChangeListener mOnPageChangeListener = new OnPageChangeListener()
@Override
public void onPageScrollStateChanged(int arg0)
// TODO Auto-generated method stub
@Override
public void onPageScrolled(int arg0, float arg1, int arg2)
// TODO Auto-generated method stub
@Override
public void onPageSelected(int selection)
// TODO Auto-generated method stub
BookPagerAdapter bookAdapter = (BookPagerAdapter)mBookPager.getAdapter();
BookPageFragment fragment = (BookPageFragment)bookAdapter.getItem(selection);
if(selection > 0)
bookAdapter.getItem(selection - 1).onPause();
// bookAdapter.getItem(selection - 1).onDestroy();
if(selection + 1 < bookAdapter.getCount() && (bookAdapter.getItem(selection + 1) != null))
bookAdapter.getItem(selection + 1).onPause();
fragment.setCurrentPage(true);
fragment.onResume();
;
public static class BookPagerAdapter extends FragmentStatePagerAdapter
private List<Fragment> mBookPagesList;
private int mReadType;
public BookPagerAdapter(FragmentManager fm,int readType)
super(fm);
// TODO Auto-generated constructor stub
mReadType = readType;
initPages();
@Override
public Fragment getItem(int position)
// TODO Auto-generated method stub
return mBookPagesList.get(position);
@Override
public int getCount()
// TODO Auto-generated method stub
return mBookPagesList.size();
private void initPages()
mBookPagesList = new ArrayList<Fragment>();
mBookPagesList.add(FirstPageFragment.newInstance(mReadType));
mBookPagesList.add(SecondPageFragment.newInstance(mReadType));
mBookPagesList.add(ThirdPageFragment.newInstance(mReadType));
mBookPagesList.add(FourthPageFragment.newInstance(mReadType));
mBookPagesList.add(FifthPageFragment.newInstance(mReadType));
mBookPagesList.add(SixthPageFragment.newInstance(mReadType));
mBookPagesList.add(SeventhPageFragment.newInstance(mReadType));
mBookPagesList.add(EigthPageFragment.newInstance(mReadType));
mBookPagesList.add(NinethPageFragment.newInstance(mReadType));
mBookPagesList.add(TenthPageFragment.newInstance(mReadType));
mBookPagesList.add(EleventhPageFragment.newInstance(mReadType));
mBookPagesList.add(TwelvethPageFragment.newInstance(mReadType));
mBookPagesList.add(ThirteenthPageFragment.newInstance(mReadType));
mBookPagesList.add(FourteenthPageFragment.newInstance(mReadType));
mBookPagesList.add(FifteenthPageFragment.newInstance(mReadType));
mBookPagesList.add(SixteenthPageFragment.newInstance(mReadType));
mBookPagesList.add(SeventeenthPageFragment.newInstance(mReadType));
mBookPagesList.add(CreditsPageFragment.newInstance(mReadType));
BookPageFragment
public abstract class BookPageFragment extends Fragment
public static final String TAG = BookPageFragment.class.getSimpleName();
public static final int AUTO_PLAY = 1;
public static final int READ_WITH_ME = 2;
public static final int READ_TO_MYSELF = 3;
private ViewPagerController mPageController;
protected final static String READ_TYPE_KEY = "readType";
private boolean mIsCurrentPage;
private int mCurrentWordIndex;
private MediaPlayer mMediaPlayer;
private BookPage mBookPage;
private SpeechController mSpeechController;
private TextHighlightController mCurrentHighlightController;
protected List<TextHighlightController> mHighlighters;
private int mCurrentHighlightIndex;
public abstract int getJsonId();
public abstract int getAudioResourceId();
protected abstract int[] getParagraphsTextView();
protected abstract int[] getParagraphsStringRes();
protected abstract int[] getPopupButtonsId();
public BookPageFragment()
mIsCurrentPage = false;
mCurrentHighlightIndex = 0;
public void endAudioPlayback()
if(getReadTypeFromArgs() == AUTO_PLAY)
mPageController.goToNextPage();
private void loadHighlighters()
int[] paragraphsTextViews = getParagraphsTextView();
int[] stringRes = getParagraphsStringRes();
for(int i=0;i<paragraphsTextViews.length;i++)
int currentParagraph = paragraphsTextViews[i];
int stringId = stringRes[i];
TextView paragraph = (TextView)getView().findViewById(currentParagraph);
TextHighlightController controller = TextHighlightController.newInstance(getActivity(), paragraph, stringId);
addHighlighter(controller);
public final void highlightNextWord()
if(!mCurrentHighlightController.highlightNextWord())
mCurrentHighlightIndex++;
if(mCurrentHighlightIndex < mHighlighters.size())
mCurrentHighlightController = mHighlighters.get(mCurrentHighlightIndex);
mCurrentHighlightController.highlightNextWord();
@Override
public void onAttach(Activity activity)
// TODO Auto-generated method stub
super.onAttach(activity);
Log.i(TAG,"onAttach");
try
mPageController = (ViewPagerController)activity;
catch(ClassCastException e)
throw new IllegalArgumentException("Activity not implementing ViewPagerController");
@Override
public void onCreate(Bundle savedInstanceState)
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
Log.i(TAG,"onCreate");
@Override
public void onDetach()
// TODO Auto-generated method stub
super.onDetach();
resetAll();
Log.i(TAG,"onDetach");
public void goToNextPage()
mPageController.goToNextPage();
public void goToPreviousPage()
mPageController.goToPreviousPage();
public void setCurrentPage(boolean isCurrentPage)
mIsCurrentPage = isCurrentPage;
public boolean isCurrentPage()
return mIsCurrentPage;
@Override
public void onStart()
// TODO Auto-generated method stub
super.onStart();
Log.i(TAG,"onStart");
@Override
public void onResume()
// TODO Auto-generated method stub
Log.i(TAG,"onResume");
super.onResume();
resetAll();
configureBookPage();
public final void startWithAutoPlay()
disablePopupButtons();
initAudioPlayback();
public final void startWithRead()
initAudioPlayback();
private long prevWordStartTime = 0;
public final long getNextWordStart()
long wordStart=-1;
if(mCurrentWordIndex < mBookPage.getWordList().size())
Word currentWord = mBookPage.getWordList().get(mCurrentWordIndex);
wordStart = currentWord.getStartTime() - prevWordStartTime;
wordStart = wordStart + currentWord.getWordLength() - 25;
prevWordStartTime = currentWord.getEndTime();
mCurrentWordIndex++;
return wordStart;
public final long getNextWordLength()
long wordLength;
if(mCurrentWordIndex < mBookPage.getWordList().size())
Word currentWord = mBookPage.getWordList().get(mCurrentWordIndex);
if(mCurrentWordIndex == 0)
wordLength= currentWord.getStartTime();
else
wordLength = currentWord.getWordLength();
mCurrentWordIndex++;
else
wordLength = -1;
return wordLength;
public final void startPlayback()
mMediaPlayer = MediaPlayer.create(getActivity(), getAudioResourceId());
mMediaPlayer.start();
@Override
public void onPause()
// TODO Auto-generated method stub
Log.i(TAG,"onPause");
mIsCurrentPage = false;
if(mSpeechController != null)
mSpeechController.stopHighlighting();
if(mMediaPlayer != null)
try
mMediaPlayer.stop();
mMediaPlayer.release();
catch(Exception e)
resetHighlighters();
resetAll();
super.onPause();
@Override
public void onStop()
// TODO Auto-generated method stub
super.onStop();
Log.i(TAG,"onStop");
protected void addHighlighter(TextHighlightController controller)
if(mHighlighters == null)
mHighlighters = new ArrayList<TextHighlightController>();
mHighlighters.add(controller);
private void resetHighlighters()
if(mHighlighters != null)
for(TextHighlightController controller : mHighlighters)
controller.reset();
mCurrentHighlightIndex = 0;
mCurrentWordIndex = 0;
private void resetAll()
mCurrentWordIndex = 0;
mCurrentHighlightIndex = 0;
if(mMediaPlayer != null)
try
mMediaPlayer.reset();
catch(Exception e)
if(mCurrentHighlightController != null)
mCurrentHighlightController.reset();
if(mSpeechController != null)
Message msg = mSpeechController.obtainMessage(SpeechController.END_AUDIO);
mSpeechController.sendMessage(msg);
if(mHighlighters != null)
for(TextHighlightController controller : mHighlighters)
controller.reset();
private void initAudioPlayback()
if(getJsonId() != 0)
initHighlightersList();
loadJson();
mSpeechController = new SpeechController(this);
Message msg = mSpeechController.obtainMessage(SpeechController.START_AUTO_PLAY);
mSpeechController.sendMessageDelayed(msg, 1000);
private void disablePopupButtons()
if(getView() != null)
int[] buttonsId = getPopupButtonsId();
for(int currentButtonId : buttonsId)
getView().findViewById(currentButtonId).setVisibility(View.INVISIBLE);
private void initHighlightersList()
loadHighlighters();
if(mHighlighters != null)
mCurrentHighlightController = mHighlighters.get(mCurrentHighlightIndex);
private void loadJson()
Gson gson = new Gson();
InputStream jsonStream = getResources().openRawResource(getJsonId());
InputStreamReader jsonReader = new InputStreamReader(jsonStream);
mBookPage = gson.fromJson(jsonReader, BookPage.class);
private void configureBookPage()
int currentReadType = getReadTypeFromArgs();
Log.i(TAG,"GotReadType");
switch(currentReadType)
case AUTO_PLAY:
if(mIsCurrentPage)
startWithAutoPlay();
break;
case READ_WITH_ME:
if(mIsCurrentPage)
startWithRead();
break;
case READ_TO_MYSELF:
//Should do Nothing
break;
default:
throw new IllegalArgumentException("You must select one of the reading types of BookPageFragment");
protected int getReadTypeFromArgs()
return getArguments().getInt(READ_TYPE_KEY);
LOGCAT
09-30 22:56:37.602: E/androidRuntime(7640): FATAL EXCEPTION: main
09-30 22:56:37.602: E/AndroidRuntime(7640): java.lang.NullPointerException
09-30 22:56:37.602: E/AndroidRuntime(7640): at com.mobimanage.kagadventures.fragment.BookPageFragment.loadHighlighters(BookPageFragment.java:68)
09-30 22:56:37.602: E/AndroidRuntime(7640): at com.mobimanage.kagadventures.fragment.BookPageFragment.initHighlightersList(BookPageFragment.java:275)
09-30 22:56:37.602: E/AndroidRuntime(7640): at com.mobimanage.kagadventures.fragment.BookPageFragment.initAudioPlayback(BookPageFragment.java:257)
09-30 22:56:37.602: E/AndroidRuntime(7640): at com.mobimanage.kagadventures.fragment.BookPageFragment.startWithRead(BookPageFragment.java:149)
09-30 22:56:37.602: E/AndroidRuntime(7640): at com.mobimanage.kagadventures.fragment.BookPageFragment.configureBookPage(BookPageFragment.java:298)
09-30 22:56:37.602: E/AndroidRuntime(7640): at com.mobimanage.kagadventures.fragment.BookPageFragment.onResume(BookPageFragment.java:140)
09-30 22:56:37.602: E/AndroidRuntime(7640): at com.mobimanage.kagadventures.MainActivity$1.onPageSelected(MainActivity.java:136)
09-30 22:56:37.602: E/AndroidRuntime(7640): at android.support.v4.view.ViewPager.scrollToItem(ViewPager.java:567)
09-30 22:56:37.602: E/AndroidRuntime(7640): at android.support.v4.view.ViewPager.setCurrentItemInternal(ViewPager.java:551)
09-30 22:56:37.602: E/AndroidRuntime(7640): at android.support.v4.view.ViewPager.onTouchEvent(ViewPager.java:2008)
09-30 22:56:37.602: E/AndroidRuntime(7640): at android.view.View.dispatchTouchEvent(View.java:7253)
09-30 22:56:37.602: E/AndroidRuntime(7640): at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2168)
09-30 22:56:37.602: E/AndroidRuntime(7640): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1903)
09-30 22:56:37.602: E/AndroidRuntime(7640): at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2174)
09-30 22:56:37.602: E/AndroidRuntime(7640): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1917)
09-30 22:56:37.602: E/AndroidRuntime(7640): at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2174)
09-30 22:56:37.602: E/AndroidRuntime(7640): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1917)
09-30 22:56:37.602: E/AndroidRuntime(7640): at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2174)
09-30 22:56:37.602: E/AndroidRuntime(7640): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1917)
09-30 22:56:37.602: E/AndroidRuntime(7640): at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2174)
09-30 22:56:37.602: E/AndroidRuntime(7640): at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1917)
09-30 22:56:37.602: E/AndroidRuntime(7640): at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:2215)
09-30 22:56:37.602: E/AndroidRuntime(7640): at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1458)
09-30 22:56:37.602: E/AndroidRuntime(7640): at android.app.Activity.dispatchTouchEvent(Activity.java:2410)
09-30 22:56:37.602: E/AndroidRuntime(7640): at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:2163)
09-30 22:56:37.602: E/AndroidRuntime(7640): at android.view.View.dispatchPointerEvent(View.java:7433)
09-30 22:56:37.602: E/AndroidRuntime(7640): at android.view.ViewRootImpl.deliverPointerEvent(ViewRootImpl.java:3220)
09-30 22:56:37.602: E/AndroidRuntime(7640): at android.view.ViewRootImpl.deliverInputEvent(ViewRootImpl.java:3165)
09-30 22:56:37.602: E/AndroidRuntime(7640): at android.view.ViewRootImpl.doProcessInputEvents(ViewRootImpl.java:4292)
09-30 22:56:37.602: E/AndroidRuntime(7640): at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:4271)
09-30 22:56:37.602: E/AndroidRuntime(7640): at android.view.ViewRootImpl$WindowInputEventReceiver.onInputEvent(ViewRootImpl.java:4363)
09-30 22:56:37.602: E/AndroidRuntime(7640): at android.view.InputEventReceiver.dispatchInputEvent(InputEventReceiver.java:179)
09-30 22:56:37.602: E/AndroidRuntime(7640): at android.os.MessageQueue.nativePollOnce(Native Method)
09-30 22:56:37.602: E/AndroidRuntime(7640): at android.os.MessageQueue.next(MessageQueue.java:125)
09-30 22:56:37.602: E/AndroidRuntime(7640): at android.os.Looper.loop(Looper.java:124)
09-30 22:56:37.602: E/AndroidRuntime(7640): at android.app.ActivityThread.main(ActivityThread.java:5227)
09-30 22:56:37.602: E/AndroidRuntime(7640): at java.lang.reflect.Method.invokeNative(Native Method)
09-30 22:56:37.602: E/AndroidRuntime(7640): at java.lang.reflect.Method.invoke(Method.java:511)
09-30 22:56:37.602: E/AndroidRuntime(7640): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:795)
09-30 22:56:37.602: E/AndroidRuntime(7640): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:562)
09-30 22:56:37.602: E/AndroidRuntime(7640): at dalvik.system.NativeStart.main(Native Method)
【问题讨论】：
你能发布相应的代码吗？ 完成！有代码 没关系。需要播种您的 PagerStateFragmentAdapter。 为了帮助我们需要查看代码以供我们分析，而不仅仅是您认为相关的代码。我们也需要查看 logcat。 有logcat，它说错误在'loadHighlighters'中，当我调试时我看到getView（）它返回null 【参考方案1】：而不是使用getItem来获取当前页面使用
(BookPageFragment) mBookPagerAdapter.instantiateItem(mBookPager, mBookPager.getCurrentItem());
这会返回一个对实际有视图的现有片段的引用。
【讨论】：
小建议：第一个mBookPager是适配器，第二个是viewPager
这个问题是双重的，但是：首先，它依赖于重写的 instantiateItem()，根据实现，它可能不仅仅是返回前一个片段，而是创建一个新片段。其次，不推荐将 View 作为第一个参数的调用。 -- 我找到了一个可行的解决方案，我会把它作为答案发布。
你救了我的命 :-)【参考方案2】：
如果您像往常一样在页面适配器中跟踪片段，请向其中添加以下函数：
private SparseArray<PageType> fragments;
...
public PageType getFragment(int position)
return fragments.get(position);
然后您可以使用它来查询片段。 getView() 已经可以正常工作了：
PageType page = (PageType) pagesAdapter.getFragment(pager.getCurrentItem());
View view = page.getView().findViewById(R.id.whatever);
view.invalidate();
【讨论】：
这真的有效吗？ Androd 可能决定销毁一个片段，它仍然在您的片段数组中，然后重新创建它，然后您的数组中有一个过时的版本。不过，我还不确定这是否会发生。【参考方案3】：对于android.support.v4.app.FragmentManager，setRetainInstance 会被忽略。
对我有用的解决方案是在调用 super.OnCreate 之前删除我活动的 onCreate 中保存的片段。
if(savedInstanceState != null)
savedInstanceState.remove("android:support:fragments");
这对我有用，就像我期望 setRetainInstance(true); 在片段本身中工作一样。
我找到了这个解决方案here
*请注意，如果您从任何片段调用 DialogFragment，如果您使用此解决方案，它们将在方向更改时关闭。
【讨论】：
以上是关于ViewPager 中的片段在 getView() 中返回 null的主要内容，如果未能解决你的问题，请参考以下文章