I am using a ViewPager fragment which has two fragments as children. This works great, however when I replace the ViewPager fragment by another fragment and replace this fragment by the ViewPager fragment my application crashes with the following NullPointerException:
java.lang.NullPointerException: Attempt to invoke virtual method 'int java.util.ArrayList.size()' on a null object reference
at android.support.v4.app.FragmentManagerImpl.getFragment(FragmentManager.java:667)
at android.support.v4.app.FragmentStatePagerAdapter.restoreState(FragmentStatePagerAdapter.java:211)
at android.support.v4.view.ViewPager.onRestoreInstanceState(ViewPager.java:1319)
at android.view.View.dispatchRestoreInstanceState(View.java:13756)
at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:2888)
at android.view.View.restoreHierarchyState(View.java:13734)
at android.support.v4.app.Fragment.restoreViewState(Fragment.java:468)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1094)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1248)
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:738)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1613)
at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:517)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5294)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:904)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:699)
My ViewPager fragment consists of the following source code instanciating the two child fragments in case they are null. Furthermore, the ViewPagerAdapter implementation is instanciated and assigned to the ViewPager.
public class ConnectionPasswordViewPagerFragment extends Fragment
{
private ViewPager vpConnectionPassword;
private ConnectionPasswordViewPagerAdapter paConnectionPassword;
private ConnectionPasswordGeneratorMACAddress passwordGeneratorMACAddress;
private ConnectionPasswordGeneratorSerialNumber passwordGeneratorSerialNumber;
public ConnectionPasswordViewPagerFragment()
{
// Required empty public constructor
}
#Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
if ((this.passwordGeneratorSerialNumber == null) && (this.passwordGeneratorMACAddress == null))
{
this.passwordGeneratorMACAddress = new ConnectionPasswordGeneratorMACAddress();
this.passwordGeneratorSerialNumber = new ConnectionPasswordGeneratorSerialNumber();
}
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState)
{
// Inflate the layout for this fragment
return inflater.inflate(R.layout.fragment_connection_password_view_pager, container, false);
}
#Override
public void onActivityCreated(Bundle savedInstanceState)
{
super.onActivityCreated(savedInstanceState);
/*if (this.paConnectionPassword == null)
{*/
this.paConnectionPassword = new ConnectionPasswordViewPagerAdapter(this.getChildFragmentManager(), this.getActivity(), this.passwordGeneratorMACAddress, this.passwordGeneratorSerialNumber);
//}
this.vpConnectionPassword = (ViewPager) this.getActivity().findViewById(R.id.vpConnectionPassword);
this.vpConnectionPassword.setAdapter(this.paConnectionPassword);
}
}
The ViewPagerAdapter shown below implementation keeps the reference to the child fragments in an ArrayList and implements the metods getItem(), getCount() as well as getPageTitle(). The class ViewPagerFragment simply extends the support Fragment class and provides the abstract method getPageTitleStringID() implemented by the child fragments.
public class ConnectionPasswordViewPagerAdapter extends FragmentStatePagerAdapter
{
private static final byte NUMBER_OF_FRAGMENTS = (byte) 2;
private ArrayList<ViewPagerFragment> childFragments;
private Activity displayActivity;
public ConnectionPasswordViewPagerAdapter(FragmentManager fragmentMgm, Activity displayAct, ConnectionPasswordGeneratorMACAddress generatorMACAddress, ConnectionPasswordGeneratorSerialNumber generatorSerialNumber)
{
super(fragmentMgm);
this.childFragments = new ArrayList<>(ConnectionPasswordViewPagerAdapter.NUMBER_OF_FRAGMENTS);
this.setDisplayActivity(displayAct);
if (generatorMACAddress != null)
{
this.childFragments.add(generatorMACAddress);
}
if (generatorSerialNumber != null)
{
this.childFragments.add(generatorSerialNumber);
}
}
public Activity getDisplayActivity()
{
return this.displayActivity;
}
public void setDisplayActivity(Activity value)
{
this.displayActivity = value;
}
#Override
public Fragment getItem(int position)
{
return this.childFragments.get(position);
}
#Override
public int getCount()
{
return ConnectionPasswordViewPagerAdapter.NUMBER_OF_FRAGMENTS;
}
#Override
public CharSequence getPageTitle(int position)
{
return this.getDisplayActivity().getString(this.childFragments.get(position).getPageTitleStringID());
}
}
Thanks for your help!
I fixed the issue by simply creating the fragment containing the view pager every time I call the support fragment manager's replace method.
public void onSwitchToConnectionPasswordGenerator(View clickedView)
{
this.fragConnectionPassword = new ConnectionPasswordViewPagerFragment();
this.getSupportFragmentManager().beginTransaction().replace(R.id.flFragmentContainer, this.fragConnectionPassword).commitAllowingStateLoss();
}
I think your Viewpager is in Fragment, and this fragment have setRetainInstance set to true (i have this error too when i try to retain the parent fragment)
Better way is to you can check for FragmentManager to get Fragment if its there, if not then create a new instance as follows:
FragmentManager manager = getSupportFragmentManager();
Fragment fragment = manager.findFragmentByTag("YourFragmentName");
if(fragment == null)
fragment = new YourFragment();
FragmentTransaction fragmentTransaction = manager.beginTransaction();
fragmentTransaction.replace(Your_Fragmnet_Container_Layout_id, fragment, fragment.getClass().getSimpleName());
fragmentTransaction.commit;
Related
I have a MainActivity inside I create ViewPager withFragments. I am using savedInstanceState to store values to set TextView after orientation changed. I also want to change value e.g. using button in MainActivity. Button works properly, but if I change the orientation then Button cannot set TextView in Fragment because TextView is now null.
MyFragment
public class MyFragment extends Fragment {
private TextView textView;
private String info;
#Nullable
#Override
public View onCreateView(#NonNull LayoutInflater inflater, #Nullable ViewGroup container, #Nullable Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.item_weather, container, false);
textView = view.findViewById(R.id.text_view);
Bundle bundle = getArguments();
info = bundle.getString("info");
setInfo(info);
return view;
}
public void setInfo(String info) {
this.info = info;
textView.setText(info); //here is the error
}
}
In MainActivity.java in OnCreate
myFragment = new MyFragment();
viewPager = findViewById(R.id.viewpager);
viewPager.setOffscreenPageLimit(10);
List<Fragment> fragments = new ArrayList<>();
fragments.add(myFragment);
pagerAdapter = new MyPageAdapter(getSupportFragmentManager(), fragments);
viewPager.setAdapter(pagerAdapter);
MyPagerAdapter looks like this:
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 fragments.get(position);
}
#Override
public int getCount() {
return fragments.size();
}
}
As I said everything works, but after orientation chage if I use Button I got an error:
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
Any ideas how to solve this?
edit:
full error
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.app.myapp, PID: 15400
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
at com.example.app.myapp.fragments.myFragment.setInfo(myFragment.java:53)
at com.example.app.myapp.MainActivity.onOptionsItemSelected(MainActivity.java:195)
at android.app.Activity.onMenuItemSelected(Activity.java:3543)
at android.support.v4.app.FragmentActivity.onMenuItemSelected(FragmentActivity.java:407)
at android.support.v7.app.AppCompatActivity.onMenuItemSelected(AppCompatActivity.java:195)
at android.support.v7.view.WindowCallbackWrapper.onMenuItemSelected(WindowCallbackWrapper.java:108)
at android.support.v7.view.WindowCallbackWrapper.onMenuItemSelected(WindowCallbackWrapper.java:108)
at android.support.v7.app.ToolbarActionBar$2.onMenuItemClick(ToolbarActionBar.java:63)
at android.support.v7.widget.Toolbar$1.onMenuItemClick(Toolbar.java:203)
at android.support.v7.widget.ActionMenuView$MenuBuilderCallback.onMenuItemSelected(ActionMenuView.java:780)
at android.support.v7.view.menu.MenuBuilder.dispatchMenuItemSelected(MenuBuilder.java:822)
at android.support.v7.view.menu.MenuItemImpl.invoke(MenuItemImpl.java:171)
at android.support.v7.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:973)
at android.support.v7.view.menu.MenuPopup.onItemClick(MenuPopup.java:127)
at android.widget.AdapterView.performItemClick(AdapterView.java:318)
at android.widget.AbsListView.performItemClick(AbsListView.java:1159)
at android.widget.AbsListView$PerformClick.run(AbsListView.java:3136)
at android.widget.AbsListView$3.run(AbsListView.java:4052)
at android.os.Handler.handleCallback(Handler.java:873)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
Into the fragment try to initialize the textView in the on the onViewCreated method:
#Override
public View onViewCreated(view: View, savedInstanceState: Bundle) {
// Your initialization code here
}
Solution:
Ok, EpicPandaForce thanks for hints.
To solve this i used in MainActivity
#Override
protected void onResume() {
super.onResume();
viewPager.setAdapter(pagerAdapter);
}
#Override
protected void onPause() {
super.onPause();
viewPager.setAdapter(null);
}
I have a HostActivity that uses ViewPager and TabLayout to switch between multiple Fragments. When I switch between the tabs, the Fragments instance does get the updated data. I also see the updated data in onCreateView of the Fragment instance, but the TextView.setText does not get updated. When I check the visibility of Fragment, it always shows Invisible. How do I make the fragment visible when I switch tabs so that the view gets updated with new data? Is there something missing in the Fragment/Activity Lifecycle? I am implementing ViewPager for the first time so it will be helpful to know if I am missing something.
Fragment Class:
public class StepFragment extends Fragment { #Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
if (getArguments() != null) {
step = getArguments().getParcelable(SELECTED_STEP);
mDescription = step.getDescription();
}
View view = inflater.inflate(R.layout.step_fragment, container, false);
ButterKnife.bind(this,view);
Log.e(TAG, "onCreateView: "+mDescription); **// THIS GETS UPDATED DATA**
tvStepDescription.setText(mDescription);
}
return view;
}
}
Here is my Host Activity:
public class StepActivity extends AppCompatActivity {
...
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_step);
fragmentSelectAdapter = new StepFragmentSelectAdapter(getSupportFragmentManager(),this,steps,recipe);
mViewPager.setAdapter(fragmentSelectAdapter);
mTabLayout.setupWithViewPager(mViewPager);
stepFragment = (StepFragment) getSupportFragmentManager().findFragmentById(R.id.step_container);
if(stepFragment == null) {
stepFragment = StepFragment.newInstance(step, recipe);
stepFragment.setArguments(bundle);
getSupportFragmentManager().beginTransaction()
.add(R.id.step_container, stepFragment)
.commit();
} else {
stepFragment = StepFragment.newInstance(step, recipe);
stepFragment.setArguments(bundle);
getSupportFragmentManager().beginTransaction()
.replace(R.id.step_container, stepFragment)
.commit();
}
}
}
Here is my FragmentPagerAdapter, which seems to be getting the correct data as per the tab position in getItem method:
public class StepFragmentSelectAdapter extends FragmentPagerAdapter {
...
#Override
public Fragment getItem(int position) {
**// THIS GETS UPDATED DATA**
Log.e(TAG, "getItem: \nDecr: "+steps.get(position).getDescription()+"\nVideo: "+steps.get(position).getVideoURL()+"\nImage: "+steps.get(position).getThumbnailURL());
return StepFragment.newInstance(steps.get(position),recipe);
}
#Override
public int getCount() {
if (steps == null){
return 0;
}
return steps.size();
}
...
}
As far as I could understand about the problem that you are having there, I think you should implement an onResume function in your StepFragment which will get the updated data from some source and will display this in the TextView. However, I can think of a potential problem in your StepFragmentSelectAdapter. You are creating a new instance each time you are switching the tabs.
You should have the Fragment instances created before and if you are about to pass the data among fragments, you might consider having a BroadcasReceiver or listener function by implementing an interface.
So the PagerAdapter should look something like this.
public class StepFragmentSelectAdapter extends FragmentPagerAdapter {
public ArrayList<StepFragment> stepFragments;
public StepFragmentSelectAdapter(ArrayList<Step> steps) {
stepFragments = new ArrayList<>();
for(int i = 0; i < steps.size(); i++) {
stepFragments.add(StepFragment.newInstance(steps.get(position),recipe));
}
}
...
#Override
public Fragment getItem(int position) {
**// THIS GETS UPDATED DATA**
Log.e(TAG, "getItem: \nDecr: "+steps.get(position).getDescription()+"\nVideo: "+steps.get(position).getVideoURL()+"\nImage: "+steps.get(position).getThumbnailURL());
return stepFragments.get(position);
}
#Override
public int getCount() {
if (steps == null){
return 0;
}
return steps.size();
}
...
}
Thanks for the hint. I got around this problem by replacing ActionBar with a custom ToolBar with back ImageButton and using click listener to get back to the calling activity.
backButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
getActivity().onBackPressed();
}
});
I occasionally get NullPointerException when entering fragment. It happens when the app was in the background for a long time and then I open it and swipe to this fragment.
public class SummaryFragment extends Fragment implements FragmentLifecycle {
private static final String TAG = "DTAG";
private DateFormat dateFormatName;
private Preference prefs;
private List<String> monthList;
private TextView totalTimeFullTv;
private TextView totalTimeNetTv;
private TextView averageTimeTv;
private TextView overUnderTv;
private TextView minTimeTv;
private TextView maxTimeTv;
private TextView vacationsTv;
private TextView sickTv;
private TextView headlineTv;
private TextView overUnderTvH;
private OnFragmentInteractionListener mListener;
public SummaryFragment() {
// Required empty public constructor
}
public static SummaryFragment newInstance(String param1, String param2) {
SummaryFragment fragment = new SummaryFragment();
return fragment;
}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View RootView = inflater.inflate(R.layout.fragment_summary, container, false);
dateFormatName = new SimpleDateFormat(getResources().getString(R.string.month_text));
monthList = Arrays.asList(new DateFormatSymbols().getMonths());
prefs = new Preference(GeneralAdapter.getContext());
totalTimeFullTv = RootView.findViewById(R.id.textView_sum_ttf);
totalTimeNetTv = RootView.findViewById(R.id.textView_sum_ttn);
averageTimeTv = RootView.findViewById(R.id.textView_sum_av);
overUnderTv = RootView.findViewById(R.id.textView_sum_ou);
overUnderTvH = RootView.findViewById(R.id.textView_sum_ou_h);
minTimeTv = RootView.findViewById(R.id.textView_sum_min);
maxTimeTv = RootView.findViewById(R.id.textView_sum_max);
vacationsTv = RootView.findViewById(R.id.textView_sum_vac);
sickTv = RootView.findViewById(R.id.textView_sum_sick);
headlineTv= RootView.findViewById(R.id.textView_sum_headline);
return RootView;
}
private void refreshData() {
if (prefs == null)
{
prefs = new Preference(GeneralAdapter.getContext());
}
String month = prefs.getString(Preference.CURRENT_MONTH);
MonthData monthData = Calculators.CalculateLocalData(MainActivity.db.getAllDays(month));
totalTimeFullTv.setText(monthData.getTotalTimeFull()); //Crash here
totalTimeNetTv.setText(monthData.getTotalTimeNet());
averageTimeTv.setText(monthData.getAverageTime());
overUnderTv.setText(monthData.getOverUnder());
if (monthData.getOverUnderFloat()<0)
{
overUnderTvH.setText(R.string.sum_over_time_neg);
overUnderTv.setTextColor(ContextCompat.getColor(GeneralAdapter.getContext(),R.color.negative_color));
}
else
{
overUnderTvH.setText(R.string.sum_over_time_pos);
overUnderTv.setTextColor(ContextCompat.getColor(GeneralAdapter.getContext(),R.color.positive_color));
}
minTimeTv.setText(monthData.getMinTime());
maxTimeTv.setText(monthData.getMaxTime());
vacationsTv.setText(""+monthData.getVacations());
sickTv.setText(""+monthData.getSick());
headlineTv.setText(month);
}
public void onButtonPressed(Uri uri) {
if (mListener != null) {
mListener.onFragmentInteraction(uri);
}
}
#Override
public void onAttachFragment(Fragment childFragment) {
super.onAttachFragment(childFragment);
}
#Override
public void onDetach() {
super.onDetach();
mListener = null;
}
#Override
public void onPauseFragment() {
}
#Override
public void onResumeFragment()
{
refreshData();
}
public interface OnFragmentInteractionListener {
// TODO: Update argument type and name
void onFragmentInteraction(Uri uri);
}
}
MainActivity viewPager:
viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
int currentPosition = 0;
#Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
}
#Override
public void onPageSelected(int position) {
FragmentLifecycle fragmentToHide = (FragmentLifecycle) adapter.getItem(currentPosition);
fragmentToHide.onPauseFragment();
FragmentLifecycle fragmentToShow = (FragmentLifecycle) adapter.getItem(position);
fragmentToShow.onResumeFragment(); //Crash start
currentPosition = position;
}
#Override
public void onPageScrollStateChanged(int state) {
}
});
Log:
E/AndroidRuntime: FATAL EXCEPTION: main
Process: michlind.com.workcalendar, PID: 25038
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
at michlind.com.workcalendar.mainfragments.SummaryFragment.refreshData(SummaryFragment.java:99)
at michlind.com.workcalendar.mainfragments.SummaryFragment.onResumeFragment(SummaryFragment.java:147)
at michlind.com.workcalendar.activities.MainActivity.onPageSelected(MainActivity.java:84)
at android.support.v4.view.ViewPager.dispatchOnPageSelected(ViewPager.java:1941)
at android.support.v4.view.ViewPager.scrollToItem(ViewPager.java:680)
at android.support.v4.view.ViewPager.setCurrentItemInternal(ViewPager.java:664)
at android.support.v4.view.ViewPager.onTouchEvent(ViewPager.java:2257)
at android.view.View.dispatchTouchEvent(View.java:11776)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2962)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2643)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2968)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2657)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2968)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2657)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2968)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2657)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2968)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2657)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2968)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2657)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2968)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2657)
at com.android.internal.policy.DecorView.superDispatchTouchEvent(DecorView.java:448)
at com.android.internal.policy.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1829)
at android.app.Activity.dispatchTouchEvent(Activity.java:3307)
at android.support.v7.view.WindowCallbackWrapper.dispatchTouchEvent(WindowCallbackWrapper.java:68)
at com.android.internal.policy.DecorView.dispatchTouchEvent(DecorView.java:410)
at android.view.View.dispatchPointerEvent(View.java:12015)
at android.view.ViewRootImpl$ViewPostImeInputStage.processPointerEvent(ViewRootImpl.java:4795)
at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:4609)
at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4147)
at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:4200)
at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:4166)
at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:4293)
at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:4174)
at android.view.ViewRootImpl$AsyncInputStage.apply(ViewRootImpl.java:4350)
at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4147)
at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:4200)
at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:4166)
at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:4174)
at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:4147)
at android.view.ViewRootImpl.deliverInputEvent(ViewRootImpl.java:6661)
at android.view.ViewRootImpl.doProcessInputEvents(ViewRootImpl.java:6635)
at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:6596)
at android.view.ViewRootImpl$WindowInputEventReceiver.onInputEvent(ViewRootImpl.java:6764)
at android.view.InputEventReceiver.dispatchInputEvent(InputEventReceiver.java:186)
at android.os.MessageQueue.nativePollOnce(Native Method)
at android.os.MessageQueue.next(MessageQueue.java:325)
at android.os.Looper.loop(Looper.java:142)
at android.app.ActivityThread.main(ActivityThread.java:6494)
UPDATE:
I eventually used:
#Override
public void onPageSelected(int position) {
Fragment fragment = adapter.getFragment(position);
if (fragment != null) {
fragment.onResume();
}
}
At my MainActivity, and used onResume() at each fragment. And this solution for the adapter:
http://thedeveloperworldisyours.com/android/update-fragment-viewpager/
The problem is, that you are trying to access views too early: view hierarchy is not created at that point yet.
If you post an event, that would take place on the next frame, you are guaranteed, that view hierarchy would be already setup:
#Override
public void onResumeFragment() {
new Handler().post(new Runnable() {
#Override
public void run() {
refreshData();
}
});
}
I faced the same problem when I had implemented custom life cycles for ViewPager. I think you are using FragmentStatePagerAdapter to populate fragments with ViewPager. As we know FragmentStatePagerAdapter destroys all the fragments when they lose focus. We need to provide same object for every page using singleton pattern.
In your code, Fragment creation can be like below for singleton pattern.
private SummaryFragment mInstance;
private SummaryFragment() {
// Required empty public constructor
}
public static SummaryFragment newInstance(String param1, String param2) {
if(mInstance == null)
mInstance = new SummaryFragment();
return mInstance;
}
Doing this has solved my problem. If this does not work for you? Can you share your PagerAdapter class.
onResumeFragment() is getting invoked before the creation of all the views of this fragment.
Try recreating newInstance first and then invoke onResumeFragment of FragmentLifeCycle interface in your Activity.
ViewPager keeps several items on either side attached (i.e. fragments resumed), however FragmentPagerAdapter uses Fragment.setUserVisibleHint to indicate, which item is current. Leverage that instead.
Here's what to do to leverage user visible hint:
Remove the OnPageChangeListener.
Ditch the FragmentLifecycle interface.
Set your fragment like so:
(in Kotlin, but you'll get the gist)
override fun setUserVisibleHint(isVisibleToUser: Boolean) {
super.setUserVisibleHint(isVisibleToUser)
if (isVisibleToUser && isResumed) {
// Do stuff.
}
}
override fun onResume() {
super.onResume()
if (userVisibleHint) {
// Do the same stuff.
}
}
More info
FragmentPagerAdapter.getItem is a factory method. It's always supposed to return you a new instance of a fragment. If you tried to cache them, remove the cache (1) and don't use getItem yourself (2).
Code that sometimes crashes and sometimes doesn't is a b**** to debug. This can be caused by reusing fragments when you're not supposed to.
A new fragment instance is not attached, has no reason to create views and will be garbage collected once you leave onPageSelected.
You are using OnPageChangeListener incorrectly. This is not a safe way to control view lifecycle events. You need to use PagerAdapter in conjunction with ViewPager and override its instantiateItem / destroyItem callbacks.
See this example: http://android-er.blogspot.com/2014/04/example-of-viewpager-with-custom.html
PagerAdapter is to ViewPager what ListAdapter is to ListView, you need both to make your system work correctly.
Use onViewCreated() callback method of fragment to update your data that way you are sure that all your views are laid out perfectly.
#Override
public void onViewCreated(View view, #Nullable Bundle savedInstanceState) {
refreshData();
}
Using Handler can still be risky as you can't be sure the view are inflated or not.
PROBLEM
The lifecycle of a Fragment is independent. You cannot be sure that when an onPageSelected() gets registered, that fragment has already been laid out. It's is an asynchronous event. So you cannot rely on this callback.
But on the other hand, you cannot also rely only on the onResume(), since in a ViewPager, the pages adjacent to the currently visible page are preloaded.
SOLUTION
Principally you will need to refreshData() when the fragment is visible to user and actively running. The definition of onResume() says the same:
Called when the fragment is visible to the user and actively running. (...)
So simply call refreshData() in the onResume() of your fragment, and don't worry if you notice this getting called while the ViewPager wasn't really showing this page.
Like most people said you need to make sure your fragment is active and visible to the user. i had a similar problem. I used onHiddenChanged to decided when to reload data.
#Override
public void onHiddenChanged(boolean hidden) {
super.onHiddenChanged(hidden);
if (!hidden) {
refreshData();
}
}
You should inflate your layout in onCreateView but shouldn't initialize other views using findViewById in onCreateView.
here is a code from the FragmentManager
// This calls onCreateView()
f.mView = f.performCreateView(f.getLayoutInflater(f.mSavedFragmentState), null, f.mSavedFragmentState);
// Null check avoids possible NPEs in onViewCreated
// It's also safe to call getView() during or after onViewCreated()
if (f.mView != null) {
f.mView.setSaveFromParentEnabled(false);
if (f.mHidden) f.mView.setVisibility(View.GONE);
f.onViewCreated(f.mView, f.mSavedFragmentState);
}
It's better to do any assignment of subviews to fields in onViewCreated. This is because the framework does an automatic null check for you to ensure that your Fragment's view hierarchy has been created and inflated (if using an XML layout file) properly.
once the view is created then initialize your views.
Add this check in refreshData() method:
if (isAdded() && getActivity() != null)
The ListView inside of a Fragment that contains a ViewPager is empty when I return back to it. This ViewPager is inside of a Fragment because I'm using a Navigation Drawer Layout. I'll try to explain it in more details now:
I am using a Navigation Drawer layout and, consequently, using Fragments. In the main activity, in onCreate, I set the current Fragment with these lines of code:
#Override
protected void onCreate(Bundle savedInstanceState) {
/* More code */
currentFragment = new MainFragment();
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction().replace(R.id.layout_for_fragments, currentFragment).commit();
}
The MainFragment class contains a ViewPager that is initialized with these lines of code in the onCreateView():
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
/* More code */
ViewPager viewPager = (ViewPager) rootView.findViewById(R.id.main_view_pager);
viewPager.setAdapter(new SimpleFragmentPagerAdapter(getActivity(), getActivity().getSupportFragmentManager()));
/* Code for Tablayout */
return rootView;
}
One of the Fragments of the SimpleFragmentPagerAdapter class is this one that implements LoaderManager.LoaderCallbacks
public class ExpensesFragment extends Fragment implements LoaderManager.LoaderCallbacks<Cursor> {
private ExpenseCursorAdapter mExpenseCursorAdapter;
private static final int EXPENSE_LOADER = 1;
public ExpensesFragment() {
// Required empty public constructor
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_expenses, container, false);
ListView expensesListView = (ListView) rootView.findViewById(R.id.expenses_list_view);
mExpenseCursorAdapter = new ExpenseCursorAdapter(getContext(), null);
expensesListView.setAdapter(mExpenseCursorAdapter);
getLoaderManager().initLoader(EXPENSE_LOADER, null, this);
return rootView;
}
#Override
public Loader<Cursor> onCreateLoader(int id, Bundle args) {
return new CursorLoader(/* arguments */);
}
#Override
public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
mExpenseCursorAdapter.swapCursor(data);
}
#Override
public void onLoaderReset(Loader<Cursor> loader) {
mExpenseCursorAdapter.swapCursor(null);
}
}
On the first run, everything works fine. However, if I click on the navigation drawer menu, which I'm implementing this way, the ListView becomes empty:
public boolean onNavigationItemSelected(#NonNull MenuItem item) {
int id = item.getItemId();
if (id == R.id.nav_main) {
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction().remove(currentFragment).commit();
currentFragment = new MainFragment();
fragmentManager.beginTransaction().replace(R.id.layout_for_fragments, currentFragment).commit();
} else if (id == R.id.nav_blank) {
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction().remove(currentFragment).commit();
currentFragment = new BlankFragment();
fragmentManager.beginTransaction().replace(R.id.layout_for_fragments, currentFragment).commit();
}
drawer.closeDrawer(GravityCompat.START);
return true;
}
The problem also exists when I rotate the device. There is a difference though. When I use the Navigation Drawer menu, none of the methods of the LoaderManager.LoaderCallbacks are called, but when I rotate the device, onLoadFinished is called.
Anyway, the problem persists. Any ideias how to solve it?
Thanks in advance.
I have found the solution!
Basically, I made two mistakes.
The first one is about the rotation of the device.
When the device is rotated, the Activity is destroyed and onCreate is called again. In this case, I should't call new MainFragment(). So, I check if the savedInstanceState is null before I call it, like this:
if (savedInstanceState == null) {
currentFragment = new MainFragment();
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction().
replace(R.id.layout_for_fragments, currentFragment).commit();
}
The second one is about a fragment within a fragment. In this case, I can't simply call getSupportFragmentManager(). I should call getChildFragmentManager() instead and that's it!
I have an activity that has a navigation drawer and a Fragment state adapter. When ever I click something in the navigation drawer I am passing that info to the mainactivity via a interface.And then I am passing that data to the main fragment which is in Fragmentstateadapter. The problem is when ever the screen rotates I get a null pointer exception for the main fragment.`
public class MainActivity extends ActionBarActivity implements RightDrawerRecyclerAdapter.Filters,
LeftDrawerFragment.MenuSection,CommonAsyncTask.ServerData {
private static final String TAG = MainActivity.class.getSimpleName();
public MainFragment mMainFragment;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ViewPager pager = (ViewPager) findViewById(R.id.pager);
ScreenSlidePagerAdapter pagerAdapter = new ScreenSlidePagerAdapter(getSupportFragmentManager());
pager.setAdapter(pagerAdapter);
}
#Override
public void getMenuSelection(int selection) {
Log.d(TAG,"getMenuSelection->"+selection);
mMainFragment.getMenuSelection(selection);
}
private class ScreenSlidePagerAdapter extends FragmentStatePagerAdapter {
public ScreenSlidePagerAdapter(FragmentManager fm) {
super(fm);
Log.d(TAG, "in screenslide");
}
#Override
public Fragment getItem(int position) {
if (position == 0) {
Log.d(TAG, "in returning MainFragment");
mMainFragment=new MainFragment();
return mMainFragment;
} else {
return new MapViewFragment();
}
}
#Override
public int getCount() {
return 2;
}
#Override
public CharSequence getPageTitle(int position) {
if (position == 0) {
return "List";
} else {
return "Map";
}
}
}}
So getMenuSelection is the method from the interface in navigation drawer. Then I have a method with the same name in my main fragment in MainFragment.So when ever I select something in the navigation drawer I can change contents in the main fragment but when ever I turn my screen a new instance of MainFragment is getting created and getItem(int position) is not getting trigged so my MainFragment object is null and now I cant pass data from my navigation drawer to main fragment.I tried making MainFragment object as static and that created problems in my MainFragment class.
So how can I get back the same MainFragment object even when the screen is turned. Or is there any better way to pass data between navigation drawer fragment and a fragment in FragmentState adapter
Hi guys I solved the problem by sending back the current instance of the MainFragment to MainActivity from onAttach via interface