getActivity returns null in Fragment function

Question

I have a fragment  F1  with a public method like this public void asd         if  getActivity      null            Log d  quot yes quot   quot it is null quot             and yes when I call it  from the Activity   it is null    FragmentTransaction transaction1   getSupportFragmentManager   beginTransaction    F1 f1   new F1    transaction1 replace R id upperPart  f1   transaction1 commit    f1 asd     It must be something that I am doing very wrong  but I don t know what that is

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 activity       mContext   context      Override public void onDetach         super onDetach        mContext   null

User · Answer

The other answers that suggest keeping a reference to the activity in onAttach are just suggesting a bandaid to the real problem  When getActivity returns null it means that the Fragment is not attached to the Activity  Most commonly this happens when the Activity has gone away due to rotation or the Activity being finished but the Fragment still has some kind of callback listener registered  When the listener gets called if you need to do something with the Activity but the Activity is gone there isn t much you can do  In your code you should just check getActivity      null and if it s not there then don t do anything  If you keep a reference to the Activity that is gone you are preventing the Activity from being garbage collected  Any UI things you might try to do won t be seen by the user  I can imagine some situations where in the callback listener you want to have a Context for something non-UI related  in those cases it probably makes more sense to get the Application context  Note that the only reason that the onAttach trick isn t a big memory leak is because normally after the callback listener executes it won t be needed anymore and can be garbage collected along with the Fragment  all its View s and the Activity context  If you setRetainInstance true  there is a bigger chance of a memory leak because the Activity field will also be retained but after rotation that could be the previous Activity not the current one

User · Answer

You can using onAttach or if you do not want to put onAttach everywhere then you can put a method that returns ApplicationContext on the main App class    public class App                 private static Context context        Override     public void onCreate             super onCreate            context   this             public static Context getContext             return context                    After that you can re-use it everywhere in all over your project  like this    App getContext   getString id    Please let me know if this does not work for you

User · Answer

Call getActivity   method inside the onActivityCreated

User · Answer

PJL is right  I have used his suggestion and this is what i have done    defined global variables for fragment   private final Object attachingActivityLock   new Object     private boolean syncVariable   false  implemented     Override public void onAttach Activity activity      super onAttach activity     synchronized  attachingActivityLock          syncVariable   true        attachingActivityLock notifyAll             3   I wrapped up my function  where I need to call getActivity    in thread  because if it would run on main thread  i would block the thread with the step 4  and onAttach   would never be called       Thread processImage   new Thread new Runnable               Override         public void run                 processImage                          processImage start      4   in my function where I need to call getActivity    I use this  before the call getActivity         synchronized  attachingActivityLock            while  syncVariable               try                   attachingActivityLock wait                  catch  InterruptedException e                       TODO Auto-generated catch block                 e printStackTrace                                    If you have some UI updates  remember to run them on UI thread  I need to update ImgeView so I did   image post new Runnable           Override     public void run             image setImageBitmap imageToShow

User · Answer

commit schedules the transaction  i e  it doesn t happen straightaway but is scheduled as work on the main thread the next time the main thread is ready    I d suggest adding an   onAttach Activity activity    method to your Fragment and putting a break point on it and seeing when it is called relative to your call to asd    You ll see that it is called after the method where you make the call to asd   exits  The onAttach call is where the Fragment is attached to its activity and from this point getActivity   will return non-null  nb there is also an onDetach   call

User · Answer

The order in which the callbacks are called after commit      Whatever method you call manually right after commit   onAttach   onCreateView   onActivityCreated     I needed to do some work that involved some Views  so onAttach   didn t work for me  it crashed  So I moved part of my code that was setting some params inside a method called right after commit    1    then the other part of the code that handled view inside onCreateView    3

User · Answer

I am using OkHttp and I just faced this issue     For the first part  thucnguyen was on the right track      This happened when you call getActivity   in another thread that finished after the fragment has been removed  The typical case is calling getActivity    ex  for a Toast  when an HTTP request finished  in onResponse for example     Some HTTP calls were being executed even after the activity had been closed  because it can take a while for an HTTP request to be completed   I then  through the HttpCallback tried to update some Fragment fields and got a null exception when trying to getActivity     http newCall request  enqueue new Callback       onResponse Call call  Response response                getActivity   runOnUiThread          lt -- getActivity   was null when it had been destroyed already   IMO the solution is to prevent callbacks to occur when the fragment is no longer alive anymore  and that s not just with Okhttp    The fix  Prevention   If you have a look at the fragment lifecycle  more info here   you ll notice that there s onAttach Context context  and onDetach   methods  These get called after the Fragment belongs to an activity and just before stop being so respectively   That means that we can prevent that callback to happen by controlling it in the onDetach method    Override public void onAttach Context context        super onAttach context           Initialize HTTP we re going to use later      http   new OkHttpClient Builder   build        Override public void onDetach         super onDetach            We don t want to receive any more information about the current HTTP calls after this point         With Okhttp we can simply cancel the on-going ones  credits to https   github com square okhttp issues 2205 issuecomment-169363942       for  Call call   http dispatcher   queuedCalls              call cancel              for  Call call   http dispatcher   runningCalls              call cancel

User · Answer

Another good solution would be using Android s LiveData with MVVM architecture  You would define a LiveData object inside your ViewModel and observe it in your fragment  and when LiveData value is changed  it would notify your observer  fragment in this case  only if your fragment is in active state  so it would be guaranteed that you would make your UI works and access the activity only when your fragment is in active state  This is one advantage that comes with LiveData  Of course when this question was first asked  there was no LiveData  I am leaving this answer here because as I see  there is still this problem and it could be helpful to someone

User · Answer

I have solved my problem this way I have passed getApplicationContext from the previous class which has already access of  getApplicationContext I have passed Inputstream object to my new class Nutrients  try                      InputStream is  getApplicationContext   getAssets   open  quot nutrient list json quot                        Nutrients nutrients Nutrients getNutrients topRecognition is                        catch  IOException e                        e printStackTrace

User · Answer

Where do you call this function  If you call it in the constructor of Fragment  it will return null   Just call getActivity   when the method onCreateView   is executed

User · Answer

Those who still have the problem with onAttach Activity activity   Its just changed to Context -        Override public void onAttach Context context        super onAttach context       this context   context      In most cases saving the context will be enough for you - for example if you want to do getResources   you can do it straight from the context  If you still need to make the context into your Activity do so -     Override public void onAttach Context context        super onAttach context       mActivity a    Your activity class - will probably be a global var      if  context instanceof mActivity           a  mActivity  context            As suggested by user1868713

User · Answer

This happened when you call getActivity   in another thread that finished after the fragment has been removed  The typical case is calling getActivity    ex  for a Toast  when an HTTP request finished  in onResponse for example    To avoid this  you can define a field name mActivity and use it instead of getActivity    This field can be initialized in onAttach   method of Fragment as following    Override public void onAttach Context context        super onAttach context        if  context instanceof Activity           mActivity   Activity  context            In my projects  I usually define a base class for all of my Fragments with this feature   public abstract class BaseFragment extends Fragment        protected FragmentActivity mActivity        Override public void onAttach Context context        super onAttach context        if  context instanceof Activity           mActivity   Activity  context              Happy coding

User · Answer

Do as follows  I think it will be helpful to you   private boolean isVisibleToUser   false  private boolean isExecutedOnce   false     Override public View onCreateView LayoutInflater inflater  ViewGroup container  Bundle savedInstanceState        View root   inflater inflate R layout fragment my  container  false       if  isVisibleToUser  amp  amp   isExecutedOnce            executeWithActivity getActivity               return root      Override public void setUserVisibleHint boolean isVisibleToUser        super setUserVisibleHint isVisibleToUser       this isVisibleToUser   isVisibleToUser      if  isVisibleToUser  amp  amp  getActivity    null            isExecutedOnce  true          executeWithActivity getActivity               private void executeWithActivity Activity activity         Do what you have to do when page is loaded with activity

User · Answer

Since Android API level 23  onAttach Activity activity  has been deprecated  You need to use onAttach Context context   http   developer android com reference android app Fragment html onAttach android app Activity   Activity is a context so if you can simply check the context is an Activity and cast it if necessary    Override public void onAttach Context context        super onAttach context        Activity a       if  context instanceof Activity           a  Activity  context

[android] getActivity() returns null in Fragment function

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