java.lang.IllegalStateException: Fragment not attached to Activity

Question

I am rarely getting this error while making an API call.

java.lang.IllegalStateException: Fragment  not attached to Activity

I tried putting the code inside isAdded() method to check whether fragment is currently added to its activity but still i rarely gets this error. I fail to understand why I am still getting this error. How can i prevent it?

Its showing error on the line-

cameraInfo.setId(getResources().getString(R.string.camera_id));

Below is the sample api call that i am making.

SAPI.getInfo(getActivity(),
                new APIResponseListener() {
                    @Override
                    public void onResponse(Object response) {


                        cameraInfo = new SInfo();
                        if(isAdded()) {
                            cameraInfo.setId(getResources().getString(R.string.camera_id));
                            cameraInfo.setName(getResources().getString(R.string.camera_name));
                            cameraInfo.setColor(getResources().getString(R.string.camera_color));
                            cameraInfo.setEnabled(true);
                        }


                    }

                    @Override
                    public void onError(VolleyError error) {
                        mProgressDialog.setVisibility(View.GONE);
                        if (error instanceof NoConnectionError) {
                            String errormsg = getResources().getString(R.string.no_internet_error_msg);
                            Toast.makeText(getActivity(), errormsg, Toast.LENGTH_LONG).show();
                        }
                    }
                });

Metallist

cameraInfo.setId(getActivity().getResources().getString(R.string.camera_id)); – Birdsong

Answer 1

This error happens due to the combined effect of two factors:

• The HTTP request, when complete, invokes either onResponse() or onError() (which work on the main thread) without knowing whether the Activity is still in the foreground or not. If the Activity is gone (the user navigated elsewhere), getActivity() returns null.
• The Volley Response is expressed as an anonymous inner class, which implicitly holds a strong reference to the outer Activity class. This results in a classic memory leak.

To solve this problem, you should always do:

Activity activity = getActivity();
if(activity != null){

    // etc ...

}

and also, use isAdded() in the onError() method as well:

@Override
public void onError(VolleyError error) {

    Activity activity = getActivity(); 
    if(activity != null && isAdded())
        mProgressDialog.setVisibility(View.GONE);
        if (error instanceof NoConnectionError) {
           String errormsg = getResources().getString(R.string.no_internet_error_msg);
           Toast.makeText(activity, errormsg, Toast.LENGTH_LONG).show();
        }
    }
}

Aplanatic

@ZyogoteInit Thanku for the answer..Yeah i saw this and i also tried it.As mentioned in question I get that exception only rarely..So I'll know only in few days that whether this completely solves my problem.Meanwhile +one for ur answer.. – Metallist

When using Volley requests and AsyncTasks from within an Activity, there is no foolproof way to avoid NPEs'. There is always the chance that the user may navigate away from the current Activity while one of the threads is doing something in the background, and then when the thread completes and onPostExecute() or onResponse() is called, there is no Activity. All you can do is make checks for null references at various points in your code, and that isn't bulletproof :) – Aplanatic

Okay..Thanks..I was using isAdded() method to check whether fragment is currently added to its activity but still rarely I was getting this exception..I hope checking whether activity is not null should completely solve my problem.. – Metallist

The android monkey test (adb shell monkey) is really good at rooting out this error if you haven't already accounted for it in a generic/global fashion. – Segregation

the isAdded() is enough, final public boolean isAdded() { return mActivity != null && mAdded; } – Cording

What does the isAdded() do? – Soothe

@ruselli: Checks the added boolean flag and whether the current Activity instance is null or not. – Aplanatic

If there are so many problems with Activity, then this should be checked in the Handler and avoid to terminate the app. Because all we do is just to ignore it. The SDK could totally handle it. – Falster

@Y.S. Can you tell how to avoid memory leak in this scenario as you stated? – Curitiba

@gauravjain Avoid making asynchronous requests (like HTTP calls) directly from Fragments. Do it from the Activity and it should be fine. Also, clear Fragment references from the FragmentManager, it's a good practice and is the best way to avoid memory leaks. – Aplanatic

How is this a solution? Sure, you no longer get the IllegalStateException and the app won't crash, but what should we actually do when the Activity is null or the Fragment is not attached to it? Your solution basically says 'Add a null check' but it doesn't say anything about what should we do to avoid the Activity becoming null, what should we do to avoid the Fragment not being attached to an Activity or what should we do when either of those cases occur. This answer is more of a workaround than actual solution. What should we do when the condition in the if statement is false? – Chorea

@VratislavJindra: As I've mentioned, the problem is caused by the fact that the Volley Response is expressed as an anonymous inner class, which implicitly holds a strong reference to the outer Activity class. An anonymous class survives garbage collection of it's enclosing class (i.e. it remains in existence), so that's why the null check. Are you aware of another solution? If so then please post it .... :) – Aplanatic

@Y.S I understand why the null check is necessary. But when the result of the null check is false, what next? You can't display any info to the user because you don't have Activity reference. The point of the onError(VolleyError error) callback is to act upon the error. The code you provided only acts when the Activity exists - but when it doesn't exist, the app hangs there and nothing happens. I'm not aware of another solution, I'm simply saying that although this solves a crash it causes another problem - the app now basically can't properly handle volley errors. – Chorea

@VratislavJindra you can add a flag to check if the data loaded or not and in onResume if not added then recall the data. – Eaglewood

are there no other cases where activity is available but this issue occurs? – Bylaw

Answer 2

Fragment lifecycle is very complex and full of bugs, try to add:

Activity activity = getActivity(); 
if (isAdded() && activity != null) {
...
}

Heteroousian

Where I should put it ? – Rhapsodist

@VaclovasRekašiusJr. Seems like pretty much anywhere you want to access the Activity from inside the fragment. Fun! – Suki

what should i do if activity == null . to keep alive my application @Miroslav – Bobo

Look into the isAdded()，you might found "activity != null" is not redundant – Sandlin

@Sandlin return mHost != null && mAdded; - That's what inside fragment.isAdded() method. I thought that mHost is an Activity if you trace it, But it seems like mHost is inside FragmentActivity. So, probably, you right. Any additions? – Dermatitis

I do it like that as well. but somehow... i still get the same error sometimes ... – Residential

Answer 3

I Found Very Simple Solution isAdded() method which is one of the fragment method to identify that this current fragment is attached to its Activity or not.

we can use this like everywhere in fragment class like:

if(isAdded())
{

// using this method, we can do whatever we want which will prevent   **java.lang.IllegalStateException: Fragment not attached to Activity** exception.

}

Adduction

Answer 4

Exception: java.lang.IllegalStateException: Fragment

DeadlineListFragment{ad2ef970} not attached to Activity

Category: Lifecycle

Description: When doing time-consuming operation in background thread(e.g, AsyncTask), a new Fragment has been created in the meantime, and was detached to the Activity before the background thread finished. The code in UI thread(e.g.,onPostExecute) calls upon a detached Fragment, throwing such exception.

Fix solution:

1. Cancel the background thread when pausing or stopping the Fragment

2. Use isAdded() to check whether the fragment is attached and then to getResources() from activity.

Unbecoming

Answer 5

i may be late but may help someone ..... The best solution for this is to create a global application class instance and call it in the particular fragment where your activity is not being attached

as like below

icon = MyApplication.getInstance().getString(R.string.weather_thunder);

Here is application class

public class MyApplication extends Application {

    private static MyApplication mInstance;
    private RequestQueue mRequestQueue;

    @Override
    public void onCreate() {
        super.onCreate();
        mInstance = this;
    }

    public static synchronized MyApplication getInstance() {
        return mInstance;
    }
}

Hurless

Yes, this method is also widely used. – Wellfixed

This is not wise option. FragmentContext and ApplicationContext have different styles. Fragment Context may have dark theme, custom style, Locale etc.. which will pull the color, string resources from different files. While ApplicationContext may not pull correct resource. If you don't have Context, then you should not be trying to render that resource. – Leith

Answer 6

In Fragment use isAdded() It will return true if the fragment is currently attached to Activity.

If you want to check inside the Activity

 Fragment fragment = new MyFragment();
   if(fragment.getActivity()!=null)
      { // your code here}
      else{
       //do something
       }

Hope it will help someone

Kele

Answer 7

This error can happen if you are instantiating a fragment that somehow can't be instantiated:

Fragment myFragment = MyFragment.NewInstance();


public classs MyFragment extends Fragment {
  public void onCreate() {
   // Some error here, or anywhere inside the class is preventing it from being instantiated
  }
}

In my case, i have met this when i tried to use:

private String loading = getString(R.string.loading);

Grekin

Answer 8

So the base idea is that you are running a UI operation on a fragment that is getting in the onDetach lifecycle.

When this is happening the fragment is getting off the stack and losing the context of the Activity.

So when you call UI related functions for example calling the progress spinner and you want to leave the fragment check if the Fragment is added to the stack, like this:

if(isAdded){ progressBar.visibility=View.VISIBLE }

Chrysanthemum

Answer 9

I adopted the following approach for handling this issue. Created a new class which act as a wrapper for activity methods like this

public class ContextWrapper {
    public static String getString(Activity activity, int resourceId, String defaultValue) {
        if (activity != null) {
            return activity.getString(resourceId);
        } else {
            return defaultValue;
        }
    }

    //similar methods like getDrawable(), getResources() etc

}

Now wherever I need to access resources from fragments or activities, instead of directly calling the method, I use this class. In case the activity context is not null it returns the value of the asset and in case the context is null, it passes a default value (which is also specified by the caller of the function).

Important This is not a solution, this is an effective way where you can handle this crash gracefully. You would want to add some logs in cases where you are getting activity instance as null and try to fix that, if possible.

Spiculum

Answer 10

This will solve your problem.

Add This on your Fragemnt

Activity activity;
@Override
public void onAttach(@NonNull Context context) {
    super.onAttach(context);
    activity = context instanceof Activity ? (Activity) context : null;
}

Then change getContext() , getActivity() , requireActivity() or requireContext() with activity

Scorch

Answer 11

this happen when the fragment does not have a context ,thus the getActivity()method return null. check if you use the context before you get it，or if the Activity is not exist anymore . use context in fragment.onCreate and after api response usually case this problem

Alger

Answer 12

Sometimes this exception is caused by a bug in the support library implementation. Recently I had to downgrade from 26.1.0 to 25.4.0 to get rid of it.

Rasp

No, I don't, but maybe I should create one. – Rasp

Answer 13

This issue occurs whenever you call a context which is unavailable or null when you call it. This can be a situation when you are calling main activity thread's context on a background thread or background thread's context on main activity thread.

For instance , I updated my shared preference string like following.

editor.putString("penname",penNameEditeText.getText().toString());
editor.commit();
finish();

And called finish() right after it. Now what it does is that as commit runs on main thread and stops any other Async commits if coming until it finishes. So its context is alive until the write is completed. Hence previous context is live , causing the error to occur.

So make sure to have your code rechecked if there is some code having this context issue.

Conchiolin

how did you manage to fix this issue? I'm calling it within an async thread and im experiencing this issue now. – Phlegmy

Just make sure that the write operation is finished , then only the context is killed not before the completion of write operation. – Conchiolin