android - viewpager - fragmentpageradapter example

Ver la excepción del puntero nulo del buscapersonas debido a la navegación de regreso al fragmento anterior-Android

Question

Estoy usando el buscapersonas para navegar entre páginas. Estoy usando FragmentStatePagerAdapter. Puedo deslizar en una dirección sin ningún problema. Pero si vuelvo al anterior. Se está cayendo. Estoy obteniendo una excepción de puntero nulo.

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)

Y aquí está mi Código:

@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;
}
}

Aquí está mi clase Fragmento:

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

Encontré la solución.

Sucede debido a FragmentStatePagerAdapter. En el fragmento, necesitamos separar el getChildFragmentManager.

Entonces, necesitamos agregar el siguiente código después de 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);
}
}