未输入事件监听器

Question

我对 Firebase 事件监听器有疑问。我正在尝试从 Firebase 数据库中获取一些数据，但无法取回结果。问题是我的听众没有运行或返回结果。我尝试使用 2 个不同的侦听器（onGetDataListener、ValueEventListener）获得结果。在调试期间，整个侦听器被跳过，调试器向前移动。我在所有侦听器阶段都添加了 Log.d，但没有一个可以访问。

public class Suggestionsfragment extends Fragment implements AdapterView.OnItemClickListener {
    private GooglePlaceList nearby;
    LinearLayout linearLayout;
    Double latitude;
    Double longitude;
    List<String> urlList;
    private List<String> interestList;
    private List<Double> latlong;


    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.suggestions, container, false);
        linearLayout = (LinearLayout) v.findViewById(R.id.main_layout);

        String placesKey = this.getResources().getString(R.string.places_key);
        interestList = new ArrayList<>();
        latlong = new ArrayList<>();
        nearby = null;
        FirebaseAuth firebaseAuth = FirebaseAuth.getInstance();
        FirebaseUser user = firebaseAuth.getCurrentUser();
        DatabaseReference databaseReference = FirebaseDatabase.getInstance().getReference();
        if (user != null) {

            DatabaseReference ref1 = databaseReference.child(user.getUid()).child("interest");
            readData(ref1, new OnGetDataListener() {
                @Override
                public void onSuccess(DataSnapshot dataSnapshot) {
                    Log.d("ONSUCCESS", "Success");
                    for (DataSnapshot postSnapshot : dataSnapshot.getChildren()) {
                        String interests = postSnapshot.getValue(String.class);
                        interestList.add(interests);
                    }
                }
                @Override
                public void onStart() {
                    //whatever you need to do onStart
                    Log.d("ONSTART", "Started");
                }

                @Override
                public void onFailure() {
                Log.d("ONFAILURE", "Failure");
                }
            });
            databaseReference.child(user.getUid());
            databaseReference.child("location");
            databaseReference.addListenerForSingleValueEvent(new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot dataSnapshot) {
                    Log.d("ONDATACHANGED", "listener2 entered");
                    try {
                        if (dataSnapshot.getValue() != null) {
                            for (DataSnapshot postSnapshot : dataSnapshot.getChildren()) {
                                Double loc = postSnapshot.getValue(Double.class);
                                latlong.add(loc);
                            }

                        }
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }

                @Override
                public void onCancelled(DatabaseError databaseError) {

                }
            });
        }
        latitude = latlong.get(0);
        longitude = latlong.get(1);

        int radius = 500;
        urlList = generateUrlList(interestList, longitude, latitude, radius, placesKey);
        if (placesKey.equals("PUT YOUR KEY HERE"))
            Toast.makeText(getActivity(), "You haven't entered your Google Places Key into the strings file.  Dont forget to set a referer too.", Toast.LENGTH_LONG).show();
        else {
            PlacesReadFeed process = new PlacesReadFeed();
            process.execute(urlList);

        }

        return v;
    }
    ...
}

Answer 1

有很多问题需要解决。

此代码不正确：

databaseReference.child(user.getUid()); // does nothing
databaseReference.child("location"); // does nothing
databaseReference.addListenerForSingleValueEvent(...);

你可能想要：

databaseReference.child(user.getUid()).child("location")
    .addListenerForSingleValueEvent(...);

你说在调试过程中整个监听器被跳过并且调试器向前移动。这是因为在将查询发送到 Firebase 服务器并收到响应之后，侦听器回调会异步触发（更多详细信息 here）。这意味着当这些语句执行时：

latitude = latlong.get(0);
longitude = latlong.get(1);

latlong 将不包含有效数据，因为onDataChange() 尚未执行。

如果您的侦听器从不触发，则可能是您没有互联网连接，或者安全规则未设置为允许读取数据。安全规则解释here。您应该将调试输出添加到onCancelled():

@Override
public void onCancelled(DatabaseError databaseError) {
    Log.e("CANCELLED", databaseError.toException());
}

我不认识OnGetDataListener()。那是你定义的类吗？

Answer 2

通过在 onDataChanged 中设置我的应用程序，我设法使用异步 firebase 获取：

@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, Bundle savedInstanceState) {
    View v = inflater.inflate(R.layout.suggestions, container, false);
    linearLayout = (LinearLayout) v.findViewById(R.id.main_layout);

    final String placesKey = this.getResources().getString(R.string.places_key);
    interestList = new ArrayList<>();
    latlong = new ArrayList<>();
    nearby = null;
    FirebaseAuth firebaseAuth = FirebaseAuth.getInstance();
    FirebaseUser user = firebaseAuth.getCurrentUser();

    if (user != null) {
        DatabaseReference ref1 = FirebaseDatabase.getInstance().getReference().child(user.getUid());
        readData(ref1, new OnGetDataListener() {
            @Override
            public void onSuccess(DataSnapshot dataSnapshot) {
                Log.d("ONSUCCESS", "Success");
                for (DataSnapshot postSnapshot : dataSnapshot.child("interest").getChildren()) {
                    String interests = postSnapshot.getValue(String.class);
                    interestList.add(interests);
                }
                for (DataSnapshot postSnapshot : dataSnapshot.child("location").getChildren()) {
                    Double loc = postSnapshot.getValue(Double.class);
                    latlong.add(loc);
                }

                latitude = latlong.get(0);
                longitude = latlong.get(1);

                int radius = 500;
                urlList = generateUrlList(interestList, longitude, latitude, radius, placesKey);
                PlacesReadFeed process = new PlacesReadFeed();
                process.execute(urlList);
            }

            @Override
            public void onStart() {
                //Whatever you want to do on start
                Log.d("ONSTART", "Started");
            }

            @Override
            public void onFailure() {
                //Whatever you want to do in case of failure
                Log.d("ONFAILURE", "Failure");
            }
        });
    }

    return v;
}

readData 和 OnGetListener 接口：

public void readData(DatabaseReference ref, final OnGetDataListener listener) {
    listener.onStart();
    ref.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            listener.onSuccess(dataSnapshot);
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {
            listener.onFailure();
        }
    });

}

interface OnGetDataListener {
    //make new interface for call back
    void onSuccess(DataSnapshot dataSnapshot);
    void onStart();
    void onFailure();
}