Android Fragment getActivity sometimes returns null

Question

In developer console error reports sometimes I see  reports with NPE issue  I do not understand what is wrong with my code  On emulator and my device application works good without forcecloses  however some users get NullPointerException in fragment class when the getActivity   method is called   Activity  pulic class MyActivity extends FragmentActivity       private ViewPager pager       private TitlePageIndicator indicator      private TabsAdapter adapter        Override     public void onCreate Bundle savedInstanceState            pager    ViewPager  findViewById R id pager           indicator    TitlePageIndicator  findViewById R id indicator           adapter   new TabsAdapter getSupportFragmentManager    false            adapter addFragment new FirstFragment             adapter addFragment new SecondFragment             indicator notifyDataSetChanged            adapter notifyDataSetChanged                push first task         FirstTask firstTask   new FirstTask MyActivity this              set first fragment as listener         firstTask setTaskListener  TaskListener  adapter getItem 0            firstTask execute               indicator setOnPageChangeListener new ViewPager OnPageChangeListener               Override         public void onPageSelected int position                Fragment currentFragment   adapter getItem position                 Taskable  currentFragment  executeTask                        Override         public void onPageScrolled int i  float v  int i1               Override         public void onPageScrollStateChanged int i                 AsyncTask class  public class FirstTask extends AsyncTask       private TaskListener taskListener                 Override     protected void onPostExecute T result                         taskListener onTaskComplete result                Fragment class  public class FirstFragment extends Fragment immplements Taskable  TaskListener       public FirstFragment                 Override     public View onCreateView LayoutInflater inflater  ViewGroup container  Bundle savedInstanceState            return inflater inflate R layout first view  container  false               Override     public void executeTask             FirstTask firstTask   new FirstTask MyActivity this           firstTask setTaskListener this           firstTask execute                Override     public void onTaskComplete T result               NPE is here          Resources res   getActivity   getResources                          Maybe this error happens when applications resumed from background  In this case how I should handle this situation properly

User · Answer

The best to get rid of this is to keep activity reference when onAttach is called and use the activity reference wherever needed, for e.g.

@Override
public void onAttach(Context context) {
    super.onAttach(context);
    mContext = context;
}

@Override
public void onDetach() {
    super.onDetach();
    mContext = null;
}

Edited, since onAttach(Activity) is depreciated & now onAttach(Context) is being used

User · Answer

In Kotlin you can try this way to handle getActivity   null condition     activity let      activity    getActivity   in java            your code here        It will check activity is null or not and if not null then execute inner code

User · Answer

Override public void onActivityCreated Bundle savedInstanceState        super onActivityCreated savedInstanceState          run the code making use of getActivity   from here

User · Answer

It seems that I found a solution to my problem  Very good explanations are given here and here  Here is my example   pulic class MyActivity extends FragmentActivity   private ViewPager pager   private TitlePageIndicator indicator  private TabsAdapter adapter  private Bundle savedInstanceState     Override public void onCreate Bundle savedInstanceState                   this savedInstanceState   savedInstanceState      pager    ViewPager  findViewById R id pager        indicator    TitlePageIndicator  findViewById R id indicator       adapter   new TabsAdapter getSupportFragmentManager    false        if  savedInstanceState    null               adapter addFragment new FirstFragment             adapter addFragment new SecondFragment          else          Integer  count    savedInstanceState getInt  tabsCount            String   titles   savedInstanceState getStringArray  titles            for  int i   0  i  lt  count  i                 adapter addFragment getFragment i   titles i                          indicator notifyDataSetChanged        adapter notifyDataSetChanged            push first task     FirstTask firstTask   new FirstTask MyActivity this          set first fragment as listener     firstTask setTaskListener  TaskListener  getFragment 0        firstTask execute        private Fragment getFragment int position        return savedInstanceState    null   adapter getItem position    getSupportFragmentManager   findFragmentByTag getFragmentTag position       private String getFragmentTag int position        return  android switcher     R id pager         position       Override protected void onSaveInstanceState Bundle outState        super onSaveInstanceState outState       outState putInt  tabsCount        adapter getCount         outState putStringArray  titles   adapter getTitles   toArray new String 0         indicator setOnPageChangeListener new ViewPager OnPageChangeListener              Override         public void onPageSelected int position                Fragment currentFragment   adapter getItem position                 Taskable  currentFragment  executeTask                        Override         public void onPageScrolled int i  float v  int i1               Override         public void onPageScrollStateChanged int i            The main idea in this code is that  while running your application normally  you create new fragments and pass them to the adapter   When you are resuming your application fragment manager already has this fragment s instance and you need to get it from fragment manager and pass it to the adapter   UPDATE  Also  it is a good practice when using fragments to check isAdded before getActivity   is called  This helps avoid a null pointer exception when the fragment is detached from the activity  For example  an activity could contain a fragment that pushes an async task  When the task is finished  the onTaskComplete listener is called    Override public void onTaskComplete List lt Feed gt  result         progress setVisibility View GONE       progress setIndeterminate false       list setVisibility View VISIBLE        if  isAdded               adapter   new FeedAdapter getActivity    R layout feed item  result           list setAdapter adapter           adapter notifyDataSetChanged               If we open the fragment  push a task  and then quickly press back to return to a previous activity  when the task is finished  it will try to access the activity in onPostExecute   by calling the getActivity   method   If the activity is already detached and this check is not there   if  isAdded       then the application crashes

User · Answer

I ve been battling this kind of problem for a while  and I think I ve come up with a reliable solution   It s pretty difficult to know for sure that this getActivity   isn t going to return null for a Fragment  especially if you re dealing with any kind of network behaviour which gives your code ample time to withdraw Activity references   In the solution below  I declare a small management class called the ActivityBuffer  Essentially  this class deals with maintaining a reliable reference to an owning Activity  and promising to execute Runnables within a valid Activity context whenever there s a valid reference available  The Runnables are scheduled for execution on the UI Thread immediately if the Context is available  otherwise execution is deferred until that Context is ready       A class which maintains a list of transactions to occur when Context becomes available     public final class ActivityBuffer            A class which defines operations to execute once there s an available Context         public interface IRunnable               Executes when there s an available Context  Ideally  will it operate immediately             void run final Activity pActivity                 Member Variables         private       Activity        mActivity      private final List lt IRunnable gt  mRunnables           Constructor         public ActivityBuffer                Initialize Member Variables          this mActivity    null          this mRunnables   new ArrayList lt IRunnable gt                    Executes the Runnable if there s an available Context  Otherwise  defers execution until it becomes available         public final void safely final IRunnable pRunnable               Synchronize along the current instance          synchronized this                   Do we have a context available              if this isContextAvailable                         Fetch the Activity                  final Activity lActivity   this getActivity                       Execute the Runnable along the Activity                  lActivity runOnUiThread new Runnable      Override public final void run     pRunnable run lActivity                                   else                      Buffer the Runnable so that it s ready to receive a valid reference                  this getRunnables   add pRunnable                                          Called to inform the ActivityBuffer that there s an available Activity reference         public final void onContextGained final Activity pActivity               Synchronize along ourself          synchronized this                   Update the Activity reference              this setActivity pActivity                  Are there any Runnables awaiting execution              if  this getRunnables   isEmpty                         Iterate the Runnables                  for final IRunnable lRunnable   this getRunnables                             Execute the Runnable on the UI Thread                      pActivity runOnUiThread new Runnable      Override public final void run                                Execute the Runnable                          lRunnable run pActivity                                                                  Empty the Runnables                  this getRunnables   clear                                           Called to inform the ActivityBuffer that the Context has been lost         public final void onContextLost                Synchronize along ourself          synchronized this                   Remove the Context reference              this setActivity null                            Defines whether there s a safe Context available for the ActivityBuffer         public final boolean isContextAvailable                Synchronize upon ourself          synchronized this                   Return the state of the Activity reference              return  this getActivity      null                           Getters and Setters         private final void setActivity final Activity pActivity            this mActivity   pActivity             private final Activity getActivity             return this mActivity             private final List lt IRunnable gt  getRunnables             return this mRunnables             In terms of its implementation  we must take care to apply the life cycle methods to coincide with the behaviour described above by Pawan M   public class BaseFragment extends Fragment           Member Variables         private ActivityBuffer mActivityBuffer       public BaseFragment                Implement the Parent          super               Allocate the ActivityBuffer          this mActivityBuffer   new ActivityBuffer                Override     public final void onAttach final Context pContext               Handle as usual          super onAttach pContext              Is the Context an Activity          if pContext instanceof Activity                   Cast Accordingly              final Activity lActivity    Activity pContext                 Inform the ActivityBuffer              this getActivityBuffer   onContextGained lActivity                         Deprecated  Override     public final void onAttach final Activity pActivity               Handle as usual          super onAttach pActivity              Inform the ActivityBuffer          this getActivityBuffer   onContextGained pActivity               Override     public final void onDetach                Handle as usual          super onDetach               Inform the ActivityBuffer          this getActivityBuffer   onContextLost                  Getters         public final ActivityBuffer getActivityBuffer             return this mActivityBuffer             Finally  in any areas within your Fragment that extends BaseFragment that you re untrustworthy about a call to getActivity    simply make a call to this getActivityBuffer   safely      and declare an ActivityBuffer IRunnable for the task    The contents of your void run final Activity pActivity  are then guaranteed to execute along the UI Thread   The ActivityBuffer can then be used as follows   this getActivityBuffer   safely    new ActivityBuffer IRunnable          Override public final void run final Activity pActivity              Do something with guaranteed Context

User · Answer

Don t call methods within the Fragment that require getActivity   until onStart in the parent Activity   private MyFragment myFragment    public void onCreate Bundle savedInstanceState        super onCreate savedInstanceState        FragmentTransaction ft   getSupportFragmentManager   beginTransaction        myFragment   new MyFragment         ft add android R id content  youtubeListFragment  commit           Other init calls                Override public void onStart         super onStart           Call your Fragment functions that uses getActivity       myFragment onPageSelected

User · Answer

I know this is a old question but i think i must provide my answer to it because my problem was not solved by others   first of all   i was dynamically adding fragments using fragmentTransactions  Second  my fragments were modified using AsyncTasks  DB queries on a server   Third  my fragment was not instantiated at activity start Fourth  i used a custom fragment instantiation  create or load it  in order to get the fragment variable  Fourth  activity was recreated because of orientation change  The problem was that i wanted to  remove  the fragment because of the query answer  but the fragment was incorrectly created just before  I don t know why  probably because of the  commit  be done later  the fragment was not added yet when it was time to remove it  Therefore getActivity   was returning null   Solution    1 I had to check that i was correctly trying to find the first instance of the fragment before creating a new one 2 I had to put serRetainInstance true  on that fragment in order to keep it through orientation change  no backstack needed therefore no problem  3 Instead of  recreating or getting old fragment  just before  remove it   I directly put the fragment at activity start  Instantiating it at activity start instead of  loading   or instantiating  the fragment variable before removing it prevented getActivity problems

User · Answer

Ok  I know that this question is actually solved but I decided to share my  solution for this  I ve created abstract parent class for my Fragment   public abstract class ABaseFragment extends Fragment       protected IActivityEnabledListener aeListener       protected interface IActivityEnabledListener          void onActivityEnabled FragmentActivity activity              protected void getAvailableActivity IActivityEnabledListener listener           if  getActivity      null               aeListener   listener             else               listener onActivityEnabled getActivity                           Override     public void onAttach Activity activity            super onAttach activity            if  aeListener    null               aeListener onActivityEnabled  FragmentActivity  activity               aeListener   null                        Override     public void onAttach Context context            super onAttach context            if  aeListener    null               aeListener onActivityEnabled  FragmentActivity  context               aeListener   null                      As you can see  I ve added a listener so  whenever I ll need to get Fragments Activity instead of standard getActivity    I ll need to call   getAvailableActivity new IActivityEnabledListener              Override         public void onActivityEnabled FragmentActivity activity                   Do manipulations with your activity

[android] Android. Fragment getActivity() sometimes returns null

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