从一个片段到另一个片段saveInstanceState不起作用

Question

Good day, I have a navigation drawer activity. Inside those are fragments. I tried using the onSavedInstanceState by changing the orientation. And yes it is working. But when i go from one fragment to another. It is not being called. Please help. The specific thing that i need to do is to save the recipients list when going back to this fragment. Thank you so much in advance. Here's my code:

 @Override
public void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
}

@Override
public View onCreateView(LayoutInflater inflater,  @Nullable ViewGroup container,
                         @Nullable Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment_recipients,container,false);
    if(savedInstanceState!=null){
        System.out.println("savedInstanceState Called!");
        saved_recipients = savedInstanceState.getStringArrayList("recipients");
        System.out.println(saved_recipients);
    }
    else{
        System.out.println("savedInstanceState not called!");
        button = (Button) view.findViewById(R.id.button);
        recipients = new ArrayList<String>();
        recipients_backend = new ArrayList<String>();
        container_recipients = (ListView) view.findViewById(R.id.listView);
        arrayAdpt= new ArrayAdapter<String>(getActivity(),
                android.R.layout.simple_list_item_1, recipients);
        container_recipients.setAdapter(arrayAdpt);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(Intent.ACTION_PICK, ContactsContract.Contacts.CONTENT_URI);
                startActivityForResult(intent, PICK_CONTACT);
            }
        });
    }
    return view;
}


@Override
public void onActivityCreated(@Nullable Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);
}

@Override
public void onActivityResult(int reqCode, int resultCode, Intent data) {
    super.onActivityResult(reqCode, resultCode, data);

    switch (reqCode) {
        case (PICK_CONTACT) :
            if (resultCode == Activity.RESULT_OK) {
                String cNumber = null;
                Uri contactData = data.getData();
                Cursor c =  getActivity().managedQuery(contactData, null, null, null, null);
                if (c.moveToFirst()) {


                    String id =c.getString(c.getColumnIndexOrThrow(ContactsContract.Contacts._ID));


                    String hasPhone =c.getString(c.getColumnIndex(ContactsContract.Contacts.HAS_PHONE_NUMBER));

                    if (hasPhone.equalsIgnoreCase("1")) {
                        Cursor phones = getActivity().getContentResolver().query(
                                ContactsContract.CommonDataKinds.Phone.CONTENT_URI,null,
                                ContactsContract.CommonDataKinds.Phone.CONTACT_ID +" = "+ id,
                                null, null);
                        phones.moveToFirst();
                        cNumber = phones.getString(phones.getColumnIndex("data1"));

                    }
                    String name = c.getString(c.getColumnIndex(ContactsContract.Contacts.DISPLAY_NAME));
                    recipients.add(name + "   " + cNumber);
                    System.out.println("New recipient added! Current list of recipients:  " + recipients);
                    if (!(recipients.isEmpty())){
                        //button.setVisibility(View.INVISIBLE);


                    }
                    else
                        // button.setVisibility(View.VISIBLE);
                        recipients_backend.add(cNumber);
                    arrayAdpt.notifyDataSetChanged();
                    System.out.println(recipients_backend);

                }
            }
            break;
    }
}
@Override
public void onSaveInstanceState(Bundle outState){
    super.onSaveInstanceState(outState);
    outState.putStringArrayList("recipients",recipients);


}

Answer 1

onSavedInstanceState is called when your fragments lifecycle is interrupted, not when it finishes normally.

You should use one of onPause , onStop or onDetach instead.

---

As the system doesn't know you plan to instantiate a new instance of your fragment, you need to save somewhere else, eg in SharedPreferences:

Get:

saved_recipients = new ArrayList(sharedPreferences.getStringSet("recipients"));

Set:

@Override
public void onPause(){
    sharedPreferences.edit().putStringSet("recipients",new HashSet(recipients)).apply();
}

---

If you do not want to save this data permanently, but only as long as the activity lives, store it in the activity itself. For Fragment-Activity-communication see Communicating between a fragment and an activity - best practices.