查看傳呼機崩潰空指針由於導航回舊片段而異常 - Android

Question

我正在使用視圖尋呼機在頁面之間進行導航。我正在使用FragmentStatePagerAdapter。我可以向一個方向滑動而不出現任何問題。但是，如果我滑回老年人。它越來越崩潰。我得到空指針異常。

03-12 10:20:34.273: E/AndroidRuntime(29035): Process: com.titlesource.notarymobile, PID: 29035 
03-12 10:20:34.273: E/AndroidRuntime(29035): java.lang.NullPointerException 
03-12 10:20:34.273: E/AndroidRuntime(29035): at android.support.v4.app.Fragment.instantiate(Fragment.java:399) 
03-12 10:20:34.273: E/AndroidRuntime(29035): at android.support.v4.app.FragmentState.instantiate(Fragment.java:97) 
03-12 10:20:34.273: E/AndroidRuntime(29035): at android.support.v4.app.FragmentManagerImpl.restoreAllState(FragmentManager.java:1790) 
03-12 10:20:34.273: E/AndroidRuntime(29035): at android.support.v4.app.Fragment.performCreate(Fragment.java:1489) 
03-12 10:20:34.273: E/AndroidRuntime(29035): at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:893) 
03-12 10:20:34.273: E/AndroidRuntime(29035): at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1104) 
03-12 10:20:34.273: E/AndroidRuntime(29035): at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682) 
03-12 10:20:34.273: E/AndroidRuntime(29035): at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1467) 
03-12 10:20:34.273: E/AndroidRuntime(29035): at android.support.v4.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:472) 
03-12 10:20:34.273: E/AndroidRuntime(29035): at android.support.v4.app.FragmentStatePagerAdapter.finishUpdate(FragmentStatePagerAdapter.java:163) 
03-12 10:20:34.273: E/AndroidRuntime(29035): at android.support.v4.view.ViewPager.populate(ViewPager.java:1068) 
03-12 10:20:34.273: E/AndroidRuntime(29035): at android.support.v4.view.ViewPager.populate(ViewPager.java:914) 
03-12 10:20:34.273: E/AndroidRuntime(29035): at android.support.v4.view.ViewPager$3.run(ViewPager.java:244) 
03-12 10:20:34.273: E/AndroidRuntime(29035): at android.view.Choreographer$CallbackRecord.run(Choreographer.java:761) 
03-12 10:20:34.273: E/AndroidRuntime(29035): at android.view.Choreographer.doCallbacks(Choreographer.java:574) 
03-12 10:20:34.273: E/AndroidRuntime(29035): at android.view.Choreographer.doFrame(Choreographer.java:543) 
03-12 10:20:34.273: E/AndroidRuntime(29035): at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:747) 
03-12 10:20:34.273: E/AndroidRuntime(29035): at android.os.Handler.handleCallback(Handler.java:733) 
03-12 10:20:34.273: E/AndroidRuntime(29035): at android.os.Handler.dispatchMessage(Handler.java:95) 
03-12 10:20:34.273: E/AndroidRuntime(29035): at android.os.Looper.loop(Looper.java:136) 
03-12 10:20:34.273: E/AndroidRuntime(29035): at android.app.ActivityThread.main(ActivityThread.java:5102) 
03-12 10:20:34.273: E/AndroidRuntime(29035): at java.lang.reflect.Method.invokeNative(Native Method) 
03-12 10:20:34.273: E/AndroidRuntime(29035): at java.lang.reflect.Method.invoke(Method.java:515) 
03-12 10:20:34.273: E/AndroidRuntime(29035): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779) 
03-12 10:20:34.273: E/AndroidRuntime(29035): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595) 
03-12 10:20:34.273: E/AndroidRuntime(29035): at dalvik.system.NativeStart.main(Native Method) 

這裏是我的代碼：

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_page_view); 
    mProgressDialog = new ProgressDialog(JobDetailsActivity.this); 
    mProgressDialog.setMessage("Loading"); 
    Bundle bundle = getIntent().getExtras(); 
    position = bundle.getInt("list_posiition_details"); 
     List<Fragment> fragments = getFragments(); 
     pageAdapter = new MyPageAdapter(getSupportFragmentManager(), fragments); 

     pager = (ViewPager)findViewById(R.id.viewpager); 
     pager.setAdapter(pageAdapter); 
     pager.setCurrentItem(position); 
     pager.setOffscreenPageLimit(3); 
} 


public interface YourFragmentInterface { 
    void fragmentBecameVisible(); 
} 

private List<Fragment> getFragments(){ 
     List<Fragment> fList = new ArrayList<Fragment>(); 

     final ArrayList<?> temp = DataModel.getScheduleList(); 

     for (final Object obj : temp) { 
      if(obj instanceof Job) { 
       String a = ((Job) obj).getA(); 
       String b = Long.toString(((Job) obj).getB()); 
       String c = ((Job) obj).getC(); 
       fList.add(JobDetailsFragment_.newInstance(a, b, c)); 
       mProgressDialog.dismiss(); 
      } 
     } 
     return fList; 
    } 


    public class MyPageAdapter extends FragmentStatePagerAdapter { 
     private List<Fragment> fragments; 

     public MyPageAdapter(FragmentManager fm, List<Fragment> fragments) { 
      super(fm); 
      this.fragments = fragments; 
     } 
     @Override 
     public Fragment getItem(int position) { 
      return this.fragments.get(position); 
     } 

     @Override 
     public int getCount() { 
      return this.fragments.size(); 
     } 

     @Override 
     public int getItemPosition(Object object) { 
      return POSITION_NONE; 
     } 

    } 

這裏是我的片段類：

public class MyFragment extends Fragment { 
public static final String EXTRA_MESSAGE = "EXTRA_MESSAGE"; 


private static View view; 
/** 
* Note that this may be null if the Google Play services APK is not 
* available. 
*/ 

SupportMapFragment mSupportMapFragment; 
private GoogleMap googleMap; 

public static final MyFragment newInstance(String message) 
{ 
    MyFragment f = new MyFragment(); 
    Bundle bdl = new Bundle(1); 
    bdl.putString(EXTRA_MESSAGE, message); 
    f.setArguments(bdl); 
    return f; 
} 
// View view; 

@Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, 
    Bundle savedInstanceState) { 
    String message = getArguments().getString(EXTRA_MESSAGE); 

    if (view != null) { 
      ViewGroup parent = (ViewGroup) view.getParent(); 
      if (parent != null) 
       parent.removeView(view); 
     } 
     try { 
      view = inflater.inflate(R.layout.myfragment_layout, container, false); 
      TextView messageTextView = (TextView)view.findViewById(R.id.textView); 
      messageTextView.setText(message); 
     } catch (InflateException e) { 
      /* map is already there, just return view as it is */ 
     } 

//  View v = inflater.inflate(R.layout.myfragment_layout, container, false); 


    return view; 
} 


@Override 
public void onActivityCreated(Bundle savedInstanceState) { 
    super.onActivityCreated(savedInstanceState); 
    FragmentManager fm = getChildFragmentManager(); 
    mSupportMapFragment = (SupportMapFragment) fm.findFragmentById(R.id.location_map); 
    if (mSupportMapFragment == null) { 
     mSupportMapFragment = SupportMapFragment.newInstance(); 
     fm.beginTransaction().replace(R.id.location_map, mSupportMapFragment).commit(); 
    } 
} 

@Override 
public void onResume() { 
    super.onResume(); 
    if (googleMap == null) { 
     googleMap = mSupportMapFragment.getMap(); 
     googleMap.addMarker(new MarkerOptions().position(new LatLng(0, 0))); 
    } 
    } 

} 

Answer 1

我找到了解決辦法。

它發生是因爲FragmentStatePagerAdapter。在片段中，我們需要分離getChildFragmentManager。

所以我們需要activityCreated（）

 @Override 
    public void onDetach() { 
     super.onDetach(); 
     try { 
      Field childFragmentManager = Fragment.class.getDeclaredField("mChildFragmentManager"); 
      childFragmentManager.setAccessible(true); 
      childFragmentManager.set(this, null); 
     } catch (NoSuchFieldException e) { 
      throw new RuntimeException(e); 
     } catch (IllegalAccessException e) { 
      throw new RuntimeException(e); 
     } 
    }