How to fix the issue when loading data from Firebase database into fragment's RecyclerView?

Question

Android

The fragment has a RecyclerView in which pictures should be loaded. However, during the test, the application crashes when switching to a fragment with this RecyclerView. How can this be fixed?

Here is the data structure in Firebase database

fragment code with RecyclerView

public class TestFragment extends Fragment {

    private ArrayList<GalleryGridObject> galleryList = new ArrayList<GalleryGridObject>();
    private TestAdapter mAdapter;
    private RecyclerView recyclerView;
    private DatabaseReference mDatabase;

    public TestFragment() {
        // Required empty public constructor
    }


    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        View view = inflater.inflate(R.layout.fragment_coupons, container, false);


        recyclerView = view.findViewById(R.id.my_recycler_view);

        LinearLayoutManager layoutManager = new LinearLayoutManager(getActivity());
        layoutManager.setOrientation(LinearLayoutManager.VERTICAL);
        recyclerView.setLayoutManager(layoutManager);
        recyclerView.hasFixedSize();
        mDatabase = FirebaseDatabase.getInstance().getReference("Data");
        mDatabase.addChildEventListener(new ChildEventListener() {
            @Override
            public void onChildAdded(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {
                for (DataSnapshot ds : dataSnapshot.getChildren()) {
                    System.out.println(ds.getValue());
                    GalleryGridObject doc = ds.getValue(GalleryGridObject.class);

                    galleryList.add(doc);

                    mAdapter = new TestAdapter(galleryList);
                    recyclerView.setAdapter(mAdapter);
                }

                mAdapter = new TestAdapter(galleryList);
                recyclerView.setAdapter(mAdapter);
            }

            @Override
            public void onChildChanged(@NonNull DataSnapshot dataSnapshot, @Nullable String s) { }

            @Override
            public void onChildRemoved(@NonNull DataSnapshot dataSnapshot) { }

            @Override
            public void onChildMoved(@NonNull DataSnapshot dataSnapshot, @Nullable String s) { }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {
                Log.w("LogFragment", "loadLog:onCancelled", databaseError.toException());
            }
        });

        return view;
    }

}

RecyclerView adapter

public class TestAdapter extends RecyclerView.Adapter<TestAdapter.ViewHolder> {

    private TestFragment mContext;
    private ArrayList<GalleryGridObject> galleryArrayList;

    public TestAdapter(ArrayList<GalleryGridObject> galleryArrayList){
        //this.mContext=mContext;
        this.galleryArrayList=galleryArrayList;
    }

    @NonNull
    @Override
    public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View itemView = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.item_coupons, parent, false);

        return new ViewHolder(itemView);
    }

    @Override
    public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
        GalleryGridObject gallery = galleryArrayList.get(position);
        Glide.with(mContext).load(gallery.getCompanyImage()).into(holder.imageGallery);
    }

    @Override
    public int getItemCount() {
        if(galleryArrayList==null) return 0;
        return galleryArrayList.size();
    }

    public class ViewHolder extends RecyclerView.ViewHolder {

        public ImageView imageGallery;

        public ViewHolder(View view) {
            super(view);
            imageGallery = itemView.findViewById(R.id.coupons_picture);
        }
    }
}

model for RecyclerView

public class GalleryGridObject {

    String companyImage;

    public GalleryGridObject () {}

    public GalleryGridObject(String companyImage) {
        this.companyImage = companyImage;
    }

    public String getCompanyImage() {
        return companyImage;
    }

    public void setGalleryImage(String galleryImage) {
        this.companyImage = galleryImage;
    }
}

logcat

com.google.firebase.database.DatabaseException: Can't convert object of type java.lang.String to type com.example.asus.socialmap.GalleryGridObject
        at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertBean(com.google.firebase:[email protected]@16.0.5:423)
        at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.deserializeToClass(com.google.firebase:[email protected]@16.0.5:214)
        at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertToCustomClass(com.google.firebase:[email protected]@16.0.5:79)
        at com.google.firebase.database.DataSnapshot.getValue(com.google.firebase:[email protected]@16.0.5:212)
        at com.example.asus.socialmap.TestFragment$1.onChildAdded(TestFragment.java:65)
        at com.google.firebase.database.core.ChildEventRegistration.fireEvent(com.google.firebase:[email protected]@16.0.5:79)
        at com.google.firebase.database.core.view.DataEvent.fire(com.google.firebase:[email protected]@16.0.5:63)
        at com.google.firebase.database.core.view.EventRaiser$1.run(com.google.firebase:[email protected]@16.0.5:55)
        at android.os.Handler.handleCallback(Handler.java:789)
        at android.os.Handler.dispatchMessage(Handler.java:98)
        at android.os.Looper.loop(Looper.java:164)
        at android.app.ActivityThread.main(ActivityThread.java:6798)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)

Answer 1

Gotta change

private ArrayList<GalleryGridObject> galleryList = new ArrayList<>();

As a private List<GalleryGridObject> galleryList;result, the fragment (or activity) code should look like this

As a result, the fragment (or activity) code should look like this

public class TestFragment extends Fragment {

private List<GalleryGridObject> galleryList;
private TestAdapter mAdapter;
private RecyclerView recyclerView;
private DatabaseReference mRef;
private FirebaseDatabase database;

public TestFragment() {
    // Required empty public constructor
}


@Override
public View onCreateView(@NonNull LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    View view = inflater.inflate(R.layout.fragment_coupons, container, false);

    recyclerView = view.findViewById(R.id.my_recycler_view);
    recyclerView.setHasFixedSize(true);
    LinearLayoutManager layoutManager = new LinearLayoutManager(getContext());
    layoutManager.setOrientation(LinearLayoutManager.VERTICAL);
    recyclerView.setLayoutManager(layoutManager);
    galleryList = new ArrayList<>();

    mAdapter = new TestAdapter(galleryList);

    database = FirebaseDatabase.getInstance();
    //mRef = database.getReference().child("Data");
    mRef = database.getReference("Data");

    mRef.addChildEventListener(new ChildEventListener() {
        @Override
        public void onChildAdded(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {
            GalleryGridObject image = dataSnapshot.getValue(GalleryGridObject.class);
            galleryList.add(image);
            recyclerView.setAdapter(mAdapter);
        }

        @Override
        public void onChildChanged(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {

        }

        @Override
        public void onChildRemoved(@NonNull DataSnapshot dataSnapshot) {

        }

        @Override
        public void onChildMoved(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {

        }

        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) {

        }
    });

    return view;
}

public class TestAdapter extends RecyclerView.Adapter<TestAdapter.ViewHolder>{
    private Context mContext;
    private List<GalleryGridObject> galleryArrayList;

    public TestAdapter( List<GalleryGridObject> galleryArrayList){
        //this.mContext=mContext;
        this.galleryArrayList=galleryArrayList;
    }

    @NonNull
    @Override
    public TestAdapter.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View itemView = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.item_coupons, parent, false);

        return new TestAdapter.ViewHolder(itemView);
    }

    @Override
    public void onBindViewHolder(@NonNull TestAdapter.ViewHolder holder, int position) {
        //GalleryGridObject gallery = galleryArrayList.get(position);
        //Glide.with(mContext).load(galleryArrayList.get(position).getImage()).into(holder.imageGallery);
        holder.textView.setText(galleryArrayList.get(position).getTitle());
        Picasso.get().load(galleryArrayList.get(position).getImage()).into(holder.imageGallery);
    }

    @Override
    public int getItemCount() {
        if(galleryArrayList==null) return 0;
        return galleryArrayList.size();
    }

    public class ViewHolder extends RecyclerView.ViewHolder {

        public ImageView imageGallery;
        public TextView textView;

        public ViewHolder(View view) {
            super(view);
            imageGallery = itemView.findViewById(R.id.coupons_picture);
            textView = itemView.findViewById(R.id.coupons_title);
        }
    }
}

}

Here is the model for the RecyclerView (an empty constructor is a must)

@IgnoreExtraProperties
public class GalleryGridObject {

String title, image;

public GalleryGridObject () {
    // Default constructor required for calls to DataSnapshot.getValue(User.class)
}

public GalleryGridObject(String title, String image) {
    this.title = title;
    this.image = image;
}

public String getTitle() {
    return title;
}

public void setTitle(String title) {
    this.title = title;
}

public String getImage() {
    return image;
}

public void setImage(String image) {
    this.image = image;
}
}

The only thing I still don’t understand is why the pictures should not immediately lie in the parent folder (in my case, Data, which we specify in mRef = database.getReference("Data");), but should have their own folders, like this (here, instead of the "Data" folder, the "KFC" folder is shown ", but the essence does not change

Obviously, in firebase you have thongs, and you are trying to read your object.

Answer 2

Obviously, in firebase you have thongs, and you are trying to read your object.