这是我目前面临的问题。我最近从带有 ADT 插件的 Eclipse 切换到 Android Studio，Android Studio 出现了一个我在 Eclipse 上从未遇到过的错误。

当我切换到名为“LineFragment”的特定 fragment 时，出现以下错误:

java.lang.NullPointerException: Attempt to write to field 'int android.support.v4.app.Fragment.mNextAnim' on a null object reference
        at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:708)
        at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1489)
        at android.support.v4.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:486)
        at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:141)
        at android.support.v4.view.ViewPager.populate(ViewPager.java:1073)
        at android.support.v4.view.ViewPager.populate(ViewPager.java:919)
        at android.support.v4.view.ViewPager$3.run(ViewPager.java:249)
        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767)
        at android.view.Choreographer.doCallbacks(Choreographer.java:580)
        at android.view.Choreographer.doFrame(Choreographer.java:549)
        at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:753)
        at android.os.Handler.handleCallback(Handler.java:739)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5221)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)

这似乎与 fragment 为空有关。我在互联网上搜索过，但很少有人遇到过类似的事情。

这是我的 fragment 的代码(它像所有 3 个 fragment 一样扩展了 android.support.v4.app.Fragment)

public class LineFragment extends Fragment{

private View v;
private ListView list;
private LineList listAdapter;
private Home home;  // Current activity

public static LineFragment  newInstance(String chaine) {
    LineFragment  fragment = new LineFragment ();
    Bundle args = new Bundle();
    args.putString("LIGNE", chaine);
    fragment.setArguments(args);
    return fragment;
}

@Override
public void onActivityCreated(Bundle savedState) {
    super.onActivityCreated(savedState);
    registerForContextMenu(list);
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
    Bundle savedInstanceState) {
    v = inflater.inflate(R.layout.fragment_ligne, container, false); 
    home = (Home) this.getActivity();
    initInterface();
    attachReactions();
    setHasOptionsMenu(true);
    return v;
}

@Override
 public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {     
    inflater.inflate(R.menu.line_menu, menu);

  MenuItem searchMenuItem = menu.findItem(R.id.action_search);

  SearchManager searchManager = (SearchManager) getActivity().getSystemService( Context.SEARCH_SERVICE );
  SearchView search = (SearchView) MenuItemCompat.getActionView(searchMenuItem);
  SearchViewCompat.setInputType(search, InputType.TYPE_CLASS_TEXT|InputType.TYPE_TEXT_VARIATION_POSTAL_ADDRESS);


search.setSearchableInfo(searchManager.getSearchableInfo(home.getComponentName()));
//search.setSubmitButtonEnabled(true);


int id = search.getContext().getResources().getIdentifier("android:id/search_src_text", null, null);
TextView textView = (TextView) search.findViewById(id);
textView.setTextColor(Color.WHITE);
textView.setHintTextColor(Color.WHITE);

search.setOnQueryTextListener(new GreenOnQueryTextListener(list));

super.onCreateOptionsMenu(menu, inflater);
 }
@Override
public void onResume() {
    super.onResume();
    Log.d("OnResume()", "Ligne");
}

@Override
public void setUserVisibleHint(boolean visible){
    super.setUserVisibleHint(visible);
    if (visible && isResumed()){
        //Only manually call onResume if fragment is already visible
        //Otherwise allow natural fragment lifecycle to call onResume
        onResume();
    }
}

/**
 * Initializes the graphical interface of the fragment.
 */
private void initInterface(){
    list = (ListView) v.findViewById(R.id.list);
    list.setTextFilterEnabled(true);
}

/**
 * Sets the reactions of the control elements
 */
private void attachReactions(){
    ArrayList<Ligne> lignes = new ArrayList<Ligne>(Globale.engine.getReseau().getLignes().values());
    listAdapter = new LineList(getActivity(), lignes);
    list.setAdapter(listAdapter);
    list.setOnItemClickListener(new LineClickListener(home));
}

这是我的 PagerAdapter :

public class KiceoFragmentPagerAdapter extends FragmentPagerAdapter{

private final int PAGE_COUNT = 3;

    public KiceoFragmentPagerAdapter(FragmentManager fm) {
        super(fm);
        // TODO Auto-generated constructor stub
    }


    @Override
    public int getCount() {
        return PAGE_COUNT;
    }

    @Override
    public Fragment getItem(int position) {     

        switch (position) {
        case 0:
            // Top Rated fragment activity
            return new LineFragment();
        case 1:
            // Games fragment activity
            return new StopFragment();
        case 2:
            // Movies fragment activity
            return new CustomMapFragment();
        }

        return new LineFragment();
    }
}

有人知道这是从哪里来的吗？它真的与 Android Studio 有关系吗？谢谢

我尝试切换到支持 V13 fragment ，但没有任何改变。

最佳答案

只需检查 getItem() 是否为 Fragment 返回了 null。如果是这样，请设置默认的 Fragment!

关于java - 切换到特定 fragment 会产生奇怪的 java.lang.NullPointerException，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/28014781/