View null inside fragment

问题

I've been working on this for hours now. Can't find any reason. I can't post the entire fragment here but the following should make it clear.

@BindView(R.id.acService) AutoCompleteTextView autocompleteService;
@BindView(R.id.acAddress) AutoCompleteTextView autocompleteAddress;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState)
{
    View view = inflater.inflate(R.layout.fragment_home, container, false);
    unbinder = ButterKnife.bind(this, view);

    initialize();
    loadSkillsData();

    return view;
}

private void initialize()
{
    context = getActivity();
    util = new Util(context);
    requestService = new RequestService();
    geoDataClient = Places.getGeoDataClient(context, null);

    autocompleteAdapter = new PlaceAutocompleteAdapter(context, geoDataClient, BOUNDS_ONTARIO, null);
    autocompleteAddress.setAdapter(autocompleteAdapter);

    mapFragment = (SupportMapFragment) getChildFragmentManager().findFragmentById(R.id.mapFragment);
    mapFragment.getMapAsync(this);
}

private void loadSkillsData()
{
    Realm realm = getRealm();
    UserModel user = realm.where(UserModel.class).findFirst();

    Retrofit retrofit = new Retrofit.Builder()
            .baseUrl(RestAPI.ENDPOINT)
            .addConverterFactory(MoshiConverterFactory.create())
            .build();
    RestAPI restApi = retrofit.create(RestAPI.class);
    Call<ResponseSkills> loginCall = restApi.getSkills(user.getServerUserId());
    loginCall.enqueue(new Callback<ResponseSkills>()
    {
        @Override
        public void onResponse(Call<ResponseSkills> call, final Response<ResponseSkills> response)
        {
            if (response.isSuccessful())
            {
                if (response.body().getStatus())
                {
                    skillList = response.body().getSkillList();
                    ArrayAdapter<SkillModel> skillAdapter = new ArrayAdapter<>(context, android.R.layout.simple_list_item_1, skillList);
                    autocompleteService.setAdapter(skillAdapter);
                }
                else
                {
                    switch (response.body().getError())
                    {
                        default:
                            Toasty.error(context, response.body().getError());
                            break;
                    }
                }
            } else
            {
                Toasty.error(context, getString(R.string.toast_experienced_a_problem)).show();
            }
        }

        @Override
        public void onFailure(Call<ResponseSkills> call, Throwable t)
        {
            Toasty.error(context, getString(R.string.toast_experienced_a_problem)).show();
            t.printStackTrace();
        }
    });
}

Layout:

On the line autocompleteService.setAdapter(skillAdapter);, I get a NPE saying that I'm calling setAdapter on a null object. Debugging tells me autocompleteService is indeed null at this point.

Why is this view null? Butterknife.bind is called way before this is. Why isn't the view initialized?

Here's the exact error:

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.AutoCompleteTextView.setAdapter(android.widget.ListAdapter)' on a null object reference
                                                            at com.xyz.controllers.HomeFragment$3.onResponse(HomeFragment.java:183)
                                                            at retrofit2.ExecutorCallAdapterFactory$ExecutorCallbackCall$1$1.run(ExecutorCallAdapterFactory.java:70)
                                                            at android.os.Handler.handleCallback(Handler.java:739)
                                                            at android.os.Handler.dispatchMessage(Handler.java:95)
                                                            at android.os.Looper.loop(Looper.java:148)
                                                            at android.app.ActivityThread.main(ActivityThread.java:5417)
                                                            at java.lang.reflect.Method.invoke(Native Method)
                                                            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                                                            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

回答1:

Override onViewCreated and move your

    unbinder = ButterKnife.bind(this, view);
    initialize();
    loadSkillsData();

into there

回答2:

Use ViewTreeObserver.onGlobalLayoutListener to make sure the view is fully laid out before attempting to mutate it. Here is your loadSkillsData function using the global layout listener which should resolve your NPE:

private void loadSkillsData()
{
    Realm realm = getRealm();
    UserModel user = realm.where(UserModel.class).findFirst();

    Retrofit retrofit = new Retrofit.Builder()
            .baseUrl(RestAPI.ENDPOINT)
            .addConverterFactory(MoshiConverterFactory.create())
            .build();
    RestAPI restApi = retrofit.create(RestAPI.class);
    Call<ResponseSkills> loginCall = restApi.getSkills(user.getServerUserId());
    loginCall.enqueue(new Callback<ResponseSkills>()
    {
        @Override
        public void onResponse(Call<ResponseSkills> call, final Response<ResponseSkills> response)
        {
            if (response.isSuccessful())
            {
                if (response.body().getStatus())
                {
                    skillList = response.body().getSkillList();
                    ArrayAdapter<SkillModel> skillAdapter = new ArrayAdapter<>(context, android.R.layout.simple_list_item_1, skillList);
                    autocompleteService.viewTreeObserver.addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
                        @Override
                        public void onGlobalLayout() {
                            autocompleteService.setAdapter(skillAdapter);
                        }
                    }
                }
                else
                {
                    switch (response.body().getError())
                    {
                        default:
                        Toasty.error(context, response.body().getError());
                        break;
                    }
                }
            } else
            {
                Toasty.error(context, getString(R.string.toast_experienced_a_problem)).show();
            }
        }

        @Override
        public void onFailure(Call<ResponseSkills> call, Throwable t)
        {
            Toasty.error(context, getString(R.string.toast_experienced_a_problem)).show();
            t.printStackTrace();
        }
    });
}

In addition to the problem with the NPE, you are also going to run into problems with the way you are using realm. Realm needs to be accessed on it's own thread, it will cause crashes in your app if you access it from the UI thread like you are doing in your code above.

回答3:

You have to call ButterKnife.bind in onCreateView method

     // bind the view using butterknife
    ButterKnife.bind(this);

来源：https://stackoverflow.com/questions/49691490/view-null-inside-fragment