令人困惑的Firestore NullPointerException或android.view.View android.view.View.findViewById（int）空对象引用

Question

我有一个问题-应用中的答案系统。我可以看到我的问题，如果我愿意，我可以回答我的问题。一切正常，但是当我“将我的问题标记为已回答”时，我得到了空值异常。当我再次运行该应用程序时，firestore和应用程序中的所有内容都可以，就像我没有空点异常一样。我不知道这是否与Firestore或其他有关。

Logcat指向此：

private void getQuestions() {

    Objects.requireNonNull( getView() ).findViewById(R.id.default_item).setVisibility(View.GONE);
    refreshLayout.setRefreshing(true);
    Query firstQuery = mFirestore.collection("Questions")
            .orderBy("timestamp", Query.Direction.DESCENDING);
    firstQuery.addSnapshotListener(new EventListener<QuerySnapshot>() {
        @Override
        public void onEvent(QuerySnapshot documentSnapshots, FirebaseFirestoreException e) {

            if (!documentSnapshots.isEmpty()) {

                for (DocumentChange doc : documentSnapshots.getDocumentChanges()) {

                    if (doc.getType() == DocumentChange.Type.ADDED) {

                        if (!Objects.equals( doc.getDocument().getString( "id" ), mCurrentUser.getUid() )) {
                            AllQuestionsModel question = doc.getDocument().toObject(AllQuestionsModel.class).withId(doc.getDocument().getId());
                            allQuestionsModelList.add(question);
                            adapter.notifyDataSetChanged();
                            refreshLayout.setRefreshing(false);
                        }

                    }

                }

                if(allQuestionsModelList.isEmpty()){
                    Objects.requireNonNull( getView() ).findViewById(R.id.default_item).setVisibility(View.VISIBLE);
                    refreshLayout.setRefreshing(false);
                }

            } else {
                Objects.requireNonNull( getView() ).findViewById(R.id.default_item).setVisibility(View.VISIBLE);
                refreshLayout.setRefreshing(false);
            }

        }

    });


}

错误：

java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference
    at eu.healthydev.quizarena.social.AllQuestionsFragment$2.onEvent(AllQuestionsFragment.java:146)
    at eu.healthydev.quizarena.social.AllQuestionsFragment$2.onEvent(AllQuestionsFragment.java:124)
    at com.google.firebase.firestore.Query.lambda$addSnapshotListenerInternal$2(com.google.firebase:firebase-firestore@@21.3.0:1025)
    at com.google.firebase.firestore.Query$$Lambda$3.onEvent(Unknown Source:6)
    at com.google.firebase.firestore.core.AsyncEventListener.lambda$onEvent$0(com.google.firebase:firebase-firestore@@21.3.0:42)
    at com.google.firebase.firestore.core.AsyncEventListener$$Lambda$1.run(Unknown Source:6)
    at android.os.Handler.handleCallback(Handler.java:790)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loop(Looper.java:164)
    at android.app.ActivityThread.main(ActivityThread.java:6494)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)

我很困惑，因为再次运行应用程序后，一切正常。有帮助吗？

更新

完整的片段代码，因为问题与视图有关：

public class AllQuestionsFragment extends Fragment {


private RecyclerView recyclerView;
private Context context;
private FirebaseFirestore mFirestore;
private FirebaseUser mCurrentUser;
private QuestionAdapter adapter;
private static String TAG= AllQuestionsFragment.class.getSimpleName();
private List<AllQuestionsModel> allQuestionsModelList =new ArrayList<>();
private TextView et0,et1,et2,et3,et4,et5,et6,et7,et8,et9,et10,et11,et12,et13;
private SwipeRefreshLayout refreshLayout;

public AllQuestionsFragment() {
}

@Override
public View onCreateView(@NonNull LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    if(getActivity().getSharedPreferences("theme",MODE_PRIVATE).getBoolean("dark",false))
        return inflater.inflate( R.layout.social_frag_answered_dark, container, false);
    else
        return inflater.inflate(R.layout.social_frag_answered_dark, container, false);
}

@Override
public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);

    context = view.getContext();
    mCurrentUser = FirebaseAuth.getInstance().getCurrentUser();

    if (mCurrentUser != null) {

        et0=view.findViewById(R.id.all);
        et1=view.findViewById(R.id.accountancy);
        et2=view.findViewById(R.id.astronomy);
        et3=view.findViewById(R.id.biology);
        et4=view.findViewById(R.id.business_maths);
        et5=view.findViewById(R.id.computer_science);
        et6=view.findViewById(R.id.commerce);
        et7=view.findViewById(R.id.chemistry);
        et8=view.findViewById(R.id.economics);
        et9=view.findViewById(R.id.geography);
        et10=view.findViewById(R.id.history);
        et11=view.findViewById(R.id.physics);
        et12=view.findViewById(R.id.p_science);
        et13=view.findViewById(R.id.maths);

        mFirestore = FirebaseFirestore.getInstance();
        adapter = new QuestionAdapter(allQuestionsModelList);
        refreshLayout=view.findViewById(R.id.refreshLayout);

        recyclerView = view.findViewById(R.id.recyclerView);
        recyclerView.setLayoutManager(new LinearLayoutManager(context));
        recyclerView.addItemDecoration(new DividerItemDecoration(context, DividerItemDecoration.VERTICAL));
        recyclerView.setItemAnimator(new DefaultItemAnimator());

        allQuestionsModelList.clear();
        recyclerView.setAdapter(adapter);

        refreshLayout.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
            @Override
            public void onRefresh() {
                allQuestionsModelList.clear();
                adapter.notifyDataSetChanged();
                getQuestions();
            }
        });

        setUpOnClick();
        getQuestions();

    }

}

private void getQuestions() {

    Objects.requireNonNull( getView() ).findViewById(R.id.default_item).setVisibility(View.GONE);
    refreshLayout.setRefreshing(true);
    Query firstQuery = mFirestore.collection("Questions")
            .orderBy("timestamp", Query.Direction.DESCENDING);
    firstQuery.addSnapshotListener(new EventListener<QuerySnapshot>() {
        @Override
        public void onEvent(QuerySnapshot documentSnapshots, FirebaseFirestoreException e) {

            if (!documentSnapshots.isEmpty()) {

                for (DocumentChange doc : documentSnapshots.getDocumentChanges()) {

                    if (doc.getType() == DocumentChange.Type.ADDED) {

                        if (!Objects.equals( doc.getDocument().getString( "id" ), mCurrentUser.getUid() )) {
                            AllQuestionsModel question = doc.getDocument().toObject(AllQuestionsModel.class).withId(doc.getDocument().getId());
                            allQuestionsModelList.add(question);
                            adapter.notifyDataSetChanged();
                            refreshLayout.setRefreshing(false);
                        }

                    }

                }

                if(allQuestionsModelList.isEmpty()){
                    Objects.requireNonNull( getView() ).findViewById(R.id.default_item).setVisibility(View.VISIBLE);
                    refreshLayout.setRefreshing(false);
                }

            } else {
                Objects.requireNonNull( getView() ).findViewById(R.id.default_item).setVisibility(View.VISIBLE);
                refreshLayout.setRefreshing(false);
            }

        }

    });


}

@Override
public void onResume() {
    super.onResume();
    adapter.notifyDataSetChanged();
}

public void filterResult(String subject){

    if(subject.equals("All")){
        getQuestions();
    }else{

        refreshLayout.setRefreshing(true);
        Objects.requireNonNull( getView() ).findViewById(R.id.default_item).setVisibility(View.GONE);

        Query firstQuery = mFirestore.collection("Questions")
                .whereEqualTo("subject",subject)
                .orderBy("timestamp", Query.Direction.DESCENDING);
        firstQuery.addSnapshotListener(getActivity(), new EventListener<QuerySnapshot>() {
            @Override
            public void onEvent(QuerySnapshot documentSnapshots, FirebaseFirestoreException e) {

                try {

                    if (!documentSnapshots.isEmpty()) {

                        for (DocumentChange doc : documentSnapshots.getDocumentChanges()) {

                            if (doc.getType() == DocumentChange.Type.ADDED) {

                                if (!doc.getDocument().getString("id").equals(mCurrentUser.getUid())) {
                                    AllQuestionsModel question = doc.getDocument().toObject(AllQuestionsModel.class).withId(doc.getDocument().getId());
                                    allQuestionsModelList.add(question);
                                    adapter.notifyDataSetChanged();
                                    refreshLayout.setRefreshing(false);
                                }

                            }



                        }
                        if(allQuestionsModelList.isEmpty()){
                            Objects.requireNonNull( getView() ).findViewById(R.id.default_item).setVisibility(View.VISIBLE);
                            refreshLayout.setRefreshing(false);
                        }

                    } else {
                        getView().findViewById(R.id.default_item).setVisibility(View.VISIBLE);
                        refreshLayout.setRefreshing(false);
                    }
                }catch (NullPointerException eee){
                    Toasty.error(context, "Some technical error occurred", Toasty.LENGTH_SHORT,true).show();
                    adapter.notifyDataSetChanged();
                    if(allQuestionsModelList.isEmpty()){
                        Objects.requireNonNull( getView() ).findViewById(R.id.default_item).setVisibility(View.VISIBLE);
                        refreshLayout.setRefreshing(false);
                    }
                } catch (Exception ee){
                    ee.printStackTrace();
                    Toasty.error(context, "Some technical error occurred", Toasty.LENGTH_SHORT, true).show();
                    if(allQuestionsModelList.isEmpty()){
                        refreshLayout.setRefreshing(false);
                        getView().findViewById(R.id.default_item).setVisibility(View.VISIBLE);
                    }
                }

            }

        });


    }

}

public void setUpOnClick(){

    et0.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            allQuestionsModelList.clear();
            adapter.notifyDataSetChanged();
            getQuestions();
            refreshLayout.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
                @Override
                public void onRefresh() {
                    allQuestionsModelList.clear();
                    adapter.notifyDataSetChanged();
                    getQuestions();
                }
            });
        }
    });
    et1.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            allQuestionsModelList.clear();
            adapter.notifyDataSetChanged();
            filterResult("Accountancy");

            refreshLayout.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
                @Override
                public void onRefresh() {
                    allQuestionsModelList.clear();
                    adapter.notifyDataSetChanged();
                    filterResult("Accountancy");
                }
            });
        }
    });
    et2.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            allQuestionsModelList.clear();
            adapter.notifyDataSetChanged();
            filterResult("Astronomy");

            refreshLayout.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
                @Override
                public void onRefresh() {
                    allQuestionsModelList.clear();
                    adapter.notifyDataSetChanged();
                    filterResult("Astronomy");
                }
            });
        }
    });
    et3.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            allQuestionsModelList.clear();
            adapter.notifyDataSetChanged();
            filterResult("Biology");

            refreshLayout.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
                @Override
                public void onRefresh() {
                    allQuestionsModelList.clear();
                    adapter.notifyDataSetChanged();
                    filterResult("Biology");
                }
            });
        }
    });
    et4.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            allQuestionsModelList.clear();
            adapter.notifyDataSetChanged();
            filterResult("Business Maths");

            refreshLayout.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
                @Override
                public void onRefresh() {
                    allQuestionsModelList.clear();
                    adapter.notifyDataSetChanged();
                    filterResult("Business Maths");
                }
            });
        }
    });
    et5.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            allQuestionsModelList.clear();
            adapter.notifyDataSetChanged();
            filterResult("Computer Science");

            refreshLayout.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
                @Override
                public void onRefresh() {
                    allQuestionsModelList.clear();
                    adapter.notifyDataSetChanged();
                    filterResult("Computer Science");
                }
            });
        }
    });
    et6.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            allQuestionsModelList.clear();
            adapter.notifyDataSetChanged();
            filterResult("Commerce");

            refreshLayout.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
                @Override
                public void onRefresh() {
                    allQuestionsModelList.clear();
                    adapter.notifyDataSetChanged();
                    filterResult("Commerce");
                }
            });
        }
    });
    et7.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            allQuestionsModelList.clear();
            adapter.notifyDataSetChanged();
            filterResult("Chemistry");

            refreshLayout.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
                @Override
                public void onRefresh() {
                    allQuestionsModelList.clear();
                    adapter.notifyDataSetChanged();
                    filterResult("Chemistry");
                }
            });
        }
    });
    et8.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            allQuestionsModelList.clear();
            adapter.notifyDataSetChanged();
            filterResult("Economics");

            refreshLayout.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
                @Override
                public void onRefresh() {
                    allQuestionsModelList.clear();
                    adapter.notifyDataSetChanged();
                    filterResult("Economics");
                }
            });
        }
    });
    et9.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            allQuestionsModelList.clear();
            adapter.notifyDataSetChanged();
            filterResult("Geography");

            refreshLayout.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
                @Override
                public void onRefresh() {
                    allQuestionsModelList.clear();
                    adapter.notifyDataSetChanged();
                    filterResult("Geography");
                }
            });
        }
    });
    et10.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            allQuestionsModelList.clear();
            adapter.notifyDataSetChanged();
            filterResult("History");

            refreshLayout.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
                @Override
                public void onRefresh() {
                    allQuestionsModelList.clear();
                    adapter.notifyDataSetChanged();
                    filterResult("History");
                }
            });
        }
    });
    et11.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            allQuestionsModelList.clear();
            adapter.notifyDataSetChanged();
            filterResult("Physics");

            refreshLayout.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
                @Override
                public void onRefresh() {
                    allQuestionsModelList.clear();
                    adapter.notifyDataSetChanged();
                    filterResult("Physics");
                }
            });
        }
    });
    et12.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            allQuestionsModelList.clear();
            adapter.notifyDataSetChanged();
            filterResult("Political Science");

            refreshLayout.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
                @Override
                public void onRefresh() {
                    allQuestionsModelList.clear();
                    adapter.notifyDataSetChanged();
                    filterResult("Political Science");
                }
            });
        }
    });
    et13.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            allQuestionsModelList.clear();
            adapter.notifyDataSetChanged();
            filterResult("Maths");

            refreshLayout.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
                @Override
                public void onRefresh() {
                    allQuestionsModelList.clear();
                    adapter.notifyDataSetChanged();
                    filterResult("Maths");
                }
            });
        }
    });

}

Answer 1

在onViewCreated内部初始化视图，如下所示。

public class AllQuestionsFragment extends Fragment {
    LinearLayout viewLayout;

    ....

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        viewLayout = view.findViewById(R.id.default_item);

        ....
    }
}

然后使用viewLayout代替下面的Objects.requireNonNull( getView() ).findViewById(R.id.default_item).setVisibility(View.GONE);

private void getQuestions() {

    viewLayout.setVisibility(View.GONE);

    ....


}