Question

我想从Firebase中获取数据并以double[]的形式输入。这是我在Firebase上的数据：

我只想获取dataSet上的数据，或者，我想以List<Double>的身份进入，那么我该如何解决呢？

已编辑

        public class ListFragment extends BaseFragment implements ListImageAdapter.OnItemClickListener {

public static final String TAG = "ListFragment";

private RecyclerView recyclerViewImages;
private FirebaseStorage mStorage;
private DatabaseReference databaseReference;
private Context context ;

private List<Model> mModel;
private ListImageAdapter listImageAdapter;
private Variable staticVariable = new Variable();

public ListFragment() {

}

@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment_list_batik, container, false);
    findView(view);
    initView(view);
    initListener(view);
    getDataFromFirebase();
    return view;
}

private void getDataFromFirebase() {
   simpleActivity.progressDialog(context);
    recyclerViewImages.setHasFixedSize(true);
    recyclerViewImages.setLayoutManager(new LinearLayoutManager(context));
    mModel = new ArrayList<>();


    listImageAdapter = new ListImageAdapter(context, mModel);
    recyclerViewImages.setAdapter(listImageAdapter);
    listImageAdapter.setOnItemClickListener(ListFragment.this);

    mStorage = FirebaseStorage.getInstance();
    databaseReference = FirebaseDatabase.getInstance().getReference(staticVariable.BATIK_DETECTIONS);
    databaseReference.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {

            mModel.clear();

            for(DataSnapshot postSnapshot : dataSnapshot.getChildren()){
                Model model = postSnapshot.getValue(Model.class);
                mModel.add(model);
            }

            listImageAdapter.notifyDataSetChanged();
        }

        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) {
            simpleActivity.toastMessage(context, databaseError.getMessage());
        }
    });
}

@Override
public void onAttach(Context context) {
    super.onAttach(context);
    this.context = context;
}

@Override
public void findView(View view) {
    recyclerViewImages = view.findViewById(R.id.recycleview_image);

}

@Override
public void initView(View view) {

}

@Override
public void initListener(View view) {

}

@Override
public void OnItemClick(int position) {
    simpleActivity.toastMessage(context, "Click on Positions : " + position);
}

@Override
public void OnViewDescriptions(int position) {
     DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
    DatabaseReference batikdetectionsRef = rootRef.child("Batikdetections");
    ValueEventListener valueEventListener = new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            for(DataSnapshot ds : dataSnapshot.getChildren()) {
                Map<String, Double> dataSet = (Map<String, Double>) ds.child("dataSet").getValue();
                double[] target = new double[dataSet.size()];
                int count = 0;
                for (Map.Entry<String, Double> entry : dataSet.entrySet()) {
                    target[count] = entry.getValue();
                    count++;
                    Log.v(TAG, String.valueOf(entry.getValue()));
                }
            }
        }

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

@Override
public void OnEditItem(int position) {
     Model selectedItem = mModel.get(position);
    String selectedKey = selectedItem.getKey();
    String selectedImage = selectedItem.getImagesUri();
    String selecteDescriptions = selectedItem.getImageDescription();
    String selectedImagesName = selectedItem.getImageNames();
    readData();
    double[] newDataSet = model.getDoubles();

    EditFragment editFragment = new EditFragment();

    FragmentTransaction fragmentTransaction =
            getActivity().getSupportFragmentManager()
                    .beginTransaction();
    Bundle bundle = new Bundle();
    bundle.putString("Label", selectedKey);
    bundle.putString("Image", selectedImage);
    bundle.putString("Descriptions", selecteDescriptions);
    bundle.putString("ImagesName", selectedImagesName);
    bundle.putDoubleArray("DataSet", newDataSet);
    editFragment.setArguments(bundle);
    fragmentTransaction.setCustomAnimations(R.anim.enter_from_right, R.anim.exit_to_right,
            R.anim.enter_from_right, R.anim.exit_to_right)
            .replace(R.id.frame_edit, editFragment)
            .addToBackStack(null)
            .commit();
}

@Override
public void OnDeleteItem(int position) {
    simpleActivity.toastMessage(context, "Delete Item :" + position);
    Model selectedItem = mModel.get(position);
    final String  selectedKey = selectedItem.getKey();

    StorageReference imageRef   = mStorage.getReferenceFromUrl(selectedItem.getImagesUri());
    imageRef.delete().addOnSuccessListener(new OnSuccessListener<Void>() {
        @Override
        public void onSuccess(Void aVoid) {
            databaseReference.child(selectedKey).removeValue();
            simpleActivity.toastMessage(context, "Item Deleted");
        }
    });
}

  public void readData(){
    DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
    DatabaseReference batikdetectionsRef = rootRef.child("Batikdetections");
    ValueEventListener valueEventListener = new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            for(DataSnapshot ds : dataSnapshot.getChildren()) {
                Map<String, Double> dataSet = (Map<String, Double>) ds.child("dataSet").getValue();
                double[] target = new double[dataSet.size()];
                int count = 0;
                for (Map.Entry<String, Double> entry : dataSet.entrySet()) {
                    target[count] = entry.getValue();
                    count++;
                    Log.d(TAG, String.valueOf(entry.getValue()));
                }
                model.setDoubles(target);
            }
        }

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

那是我的完整代码，我想要的数据是double[]，因为我喜欢在片段之间传输数据。

错误

06-12 01:51:28.424 14704-14704/com.tugasakhir.batikdetections E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.tugasakhir.batikdetections, PID: 14704
java.lang.ClassCastException: java.util.ArrayList cannot be cast to java.util.Map
    at com.tugasakhir.batikdetections.fragment.batiklopedia.ListFragment$2.onDataChange(ListFragment.java:137)
    at com.google.firebase.database.Query$1.onDataChange(com.google.firebase:firebase-database@@16.0.6:183)
    at com.google.firebase.database.core.ValueEventRegistration.fireEvent(com.google.firebase:firebase-database@@16.0.6:75)
    at com.google.firebase.database.core.view.DataEvent.fire(com.google.firebase:firebase-database@@16.0.6:63)
    at com.google.firebase.database.core.view.EventRaiser$1.run(com.google.firebase:firebase-database@@16.0.6:55)
    at android.os.Handler.handleCallback(Handler.java:733)
    at android.os.Handler.dispatchMessage(Handler.java:95)
    at android.os.Looper.loop(Looper.java:136)
    at android.app.ActivityThread.main(ActivityThread.java:5001)
    at java.lang.reflect.Method.invokeNative(Native Method)
    at java.lang.reflect.Method.invoke(Method.java:515)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
    at dalvik.system.NativeStart.main(Native Method)

Answer 1

使用ValueEventListener在您的子数据集上循环

    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for(DataSnapshot ds : dataSnapshot.getChildren()) {
         //use int i and initialize it with 0 
         Double value = (Double) dataSnapshot.child(String.valueOf(i)).getValue();
         ///listDouble is an example of Double[] array 
         listDouble[i] = value;
         i++;
        }
    }

Answer 2

代码中的主要问题是，由于方法的原因，您无法返回target数组。这是因为您尝试使用尚未从数据库加载的元素填充该数组。这是因为beucase onDataChange()方法具有异步行为。有关更多详细信息，请参见以下帖子中的答案：

How to return DataSnapshot value as a result of a method?

要解决此问题，请使用以下代码行：

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference batikdetectionsRef = rootRef.child("Batikdetections");
ValueEventListener valueEventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for(DataSnapshot ds : dataSnapshot.getChildren()) {
            ArrayList<Double> dataSet = (ArrayList<Double>) ds.child("dataSet").getValue();
            double[] target = new double[dataSet.size()];
            int count = 0;
            for (Double d : dataSet) {
                target[count] = d;
                count++;
                Log.d(TAG, String.valueOf(d));
            }

            //Do what you need to do with your target array
        }
    }

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

如何在Firebase上获取double []数组数据？

2 个答案: