java - 如何在 Firebase 中调用内部字段

Question

您好，我还是 Firebase 的新手，如何调用内部字段 latitude 和 ongitude 字段？我是否以正确的方式构建数据库？

我尝试阅读 Google 的文档，但仍然不起作用。

//Write a message to the database
public class LocationActivity extends AppCompatActivity {

    private static final String TAG = "LocationActivity";
    private RecyclerView.LayoutManager layoutManager;
    private Query query;
    private RecyclerView recyclerView;
    public FirebaseRecyclerAdapter<LocationContent,LocationViewHolder> firebaseRecyclerAdapter;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_location);

        // Write a message to the database
        query = FirebaseDatabase.getInstance()
                .getReference()
                .child("Locations")
                .limitToLast(50);

        query.keepSynced(true);

        // set up the RecyclerView
        recyclerView = findViewById(R.id.myrecyclerview);
        // use this setting to improve performance if you know that changes
        // in content do not change the layout size of the RecyclerView
        recyclerView.setHasFixedSize(true);

        // use a linear layout manager
        layoutManager = new LinearLayoutManager(this);
        recyclerView.setLayoutManager(layoutManager);

        FirebaseRecyclerOptions<LocationContent> options =
                new FirebaseRecyclerOptions.Builder<LocationContent>()
                        .setQuery(query, LocationContent.class)
                        .build();

        ValueEventListener valueEventListener = new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                for(DataSnapshot ds : dataSnapshot.getChildren()) {
                    LocationContent lc = ds.child("South Bound").getValue(LocationContent.class);
                    Log.d(TAG,"Error onDataChange");
                }
            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {
                Log.d(TAG, databaseError.getMessage()); //Don't ignore errors!
            }
        };
        query.addListenerForSingleValueEvent(valueEventListener);

        firebaseRecyclerAdapter= new FirebaseRecyclerAdapter<LocationContent, LocationViewHolder>(options) {

            @Override
            protected void onBindViewHolder(@NonNull LocationViewHolder holder, int position, @NonNull LocationContent model) {
                String doubleLatitude = Double.toString(model.getLatitude());
                String doubleLongitude = Double.toString(model.getLongitude());

                holder.post_name.setText(model.getName());
                holder.post_latitude.setText(doubleLatitude);
                holder.post_longitude.setText(doubleLongitude);
            }

            @NonNull
            @Override
            public LocationViewHolder onCreateViewHolder(@NonNull ViewGroup viewgroup, int i) {
                View view = LayoutInflater.from(viewgroup.getContext()).inflate(R.layout.location_row,viewgroup,false);

                return new LocationViewHolder(view);
            }
        };

        recyclerView.setAdapter(firebaseRecyclerAdapter);
    }

    @Override
    protected void onStart(){
        super.onStart();
        firebaseRecyclerAdapter.startListening();

    }

    @Override
    protected void onStop() {
        super.onStop();
        firebaseRecyclerAdapter.stopListening();
    }

这是我的模型

public class LocationContent {
    private String Name;
    private Double Latitude;
    private Double Longitude;

    public LocationContent(String name, Double latitude, Double longitude) {
        Name = name;
        Latitude = latitude;
        Longitude = longitude;
    }

    public LocationContent(){

    }

    public String getName() {
        return Name;
    }

    public void setName(String name) {
        Name = name;
    }

    public Double getLatitude() {
        return Latitude;
    }

    public void setLatitude(Double latitude) {
        Latitude = latitude;
    }

    public Double getLongitude() {
        return Longitude;
    }

    public void setLongitude(Double longitude) {
        Longitude = longitude;
    }

}

Answer 1

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference locationsRef = rootRef.child("Locations");
ValueEventListener valueEventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for(DataSnapshot ds : dataSnapshot.getChildren()) {
            double lat = ds.child("South Bound").child("Latitude").getValue(Double.class);
            double lng = ds.child("South Bound").child("Longitude").getValue(Double.class);
            Log.d(TAG, lat, ", " + lng);
        }
    }

    @Override
    public void onCancelled(@NonNull DatabaseError databaseError) {
        Log.d(TAG, databaseError.getMessage()); //Don't ignore errors!
    }
};
locationsRef.addListenerForSingleValueEvent(valueEventListener);

或者使用您的LocationContent类:

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference locationsRef = rootRef.child("Locations");
ValueEventListener valueEventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for(DataSnapshot ds : dataSnapshot.getChildren()) {
            LocationContent lc = ds.child("South Bound").getValue(LocationContent.class);
            Log.d(TAG, lc.getLatitude(), ", " + lc.getLongitude());
        }
    }

    @Override
    public void onCancelled(@NonNull DatabaseError databaseError) {
        Log.d(TAG, databaseError.getMessage()); //Don't ignore errors!
    }
};
locationsRef.addListenerForSingleValueEvent(valueEventListener);

如果您打算使用第二种解决方案，还请注意数据库中的字段名称与 LocationContent 类中的字段名称。因此，还请参阅我在以下帖子中的回答:

• Firebase Android ListView not being displayed

编辑:

public LocationContent(String name, double latitude, double longitude) {
    Name = name;
    Latitude = latitude;
    Longitude = longitude;
}

public LocationContent(){

}

public String getName() {
    return Name;
}

public void setName(String name) {
    Name = name;
}

public double getLatitude() {
    return Latitude;
}

public void setLatitude(double latitude) {
    Latitude = latitude;
}

public double getLongitude() {
    return Longitude;
}

public void setLongitude(double longitude) {
    Longitude = longitude;
}