RecyclerView does not display any data

Question

I've been struggling with this issue for a while. I have an activity (SerieActivity) where I allow the user to select various items and give them values. The items are stored in an ArrayList<Variable>, where Variable is a class that I've defined. The items are displayed in a RecyclerView. This works just fine. Upon clicking a button in that activity, the user is sent to another activity (Result) that displays the exact same items from the ArrayList in SerieActivity, with the respective values that the user has input.

In my Result activity I have created an instance of the SerieActivity class and then made an ArrayList to store the values of the original ArrayList from SerieActivity. However it seems like the RecyclerView from my Result class doesn't get populated with data. What could be going wrong?

Here's my code:

Variable class

public class Variable {

    boolean known;
    String unit, name;
    double value;
}

RVAdapterSerie - the adapter for the RecyclerView used in the SerieActivity class

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

    private Context context;
    private ArrayList<Variable> variableList;

    public RVAdapterSerie(Context context, ArrayList<Variable> variableList) {
        this.context = context;
        this.variableList = variableList;
    }

    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(context).inflate(R.layout.recycler_item, parent, false);
        return new ViewHolder(view);
    }

    @Override
    public void onBindViewHolder(RVAdapterSerie.ViewHolder holder, int position) {
        Variable v = variableList.get(position);
        holder.setItems(v);
    }

    @Override
    public int getItemCount() {
        return variableList.size();
    }

    public class ViewHolder extends RecyclerView.ViewHolder {
        private CheckBox checkBox;
        private EditText editText;
        private TextView textView;

        public ViewHolder(View itemView) {
            super(itemView);
            checkBox = itemView.findViewById(R.id.value_cb);
            editText = itemView.findViewById(R.id.value_et);
            textView = itemView.findViewById(R.id.value_tv);
        }

        public void setItems (Variable variable) {
            checkBox.setText(variable.getName());
            editText.setText(String.format("%.3f", variable.getValue()));
            textView.setText(variable.getUnit());
        }
    }
}

SerieActivity class

public class SerieActivity extends AppCompatActivity {

    public ArrayList<Variable> mList = new ArrayList<>();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_serie);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        RecyclerView recyclerView = findViewById(R.id.serie_rv);
        RVAdapterSerie rvAdapterSerie = new RVAdapterSerie(this, mList);
        recyclerView.setAdapter(rvAdapterSerie);
        recyclerView.setHasFixedSize(true);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));


        populateList();
        rvAdapterSerie.notifyDataSetChanged();

        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.serie_fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent(SerieActivity.this, Result.class);
                intent.putExtra("tag", "serie");
                startActivity(intent);
            }
        });
    }

    public void populateList() {
        mList.add(new Variable(false, "dummyunit", "dummyname", 0));
        mList.add(new Variable(false, "diofishafuio", "ghfuef", 0));
        mList.add(new Variable(false, "diofishdfesffafuio", "ghfuef", 0));
        //add dummy items
    }
}

---

RVResultAdapter - adapter for the RecyclerView in Result class

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

    private Context context;
    private ArrayList<Variable> variableList;

    public RVResultAdapter(Context context, ArrayList<Variable> variableList) {
        this.context = context;
        this.variableList = variableList;
    }

    @Override
    public RVResultAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(context).inflate(R.layout.result_item, parent, false);
        return new ViewHolder(view);
    }

    @Override
    public void onBindViewHolder(RVResultAdapter.ViewHolder holder, int position) {
        Variable v = variableList.get(position);
        holder.setItems(v);
    }

    @Override
    public int getItemCount() {
        return variableList.size();
    }

    public class ViewHolder extends RecyclerView.ViewHolder {

        TextView textView1;
        TextView textView2;
        TextView textView3;

        public ViewHolder(View itemView) {
            super(itemView);
            textView1 = itemView.findViewById(R.id.result_name_tv);
            textView2 = itemView.findViewById(R.id.result_value_tv);
            textView3 = itemView.findViewById(R.id.result_unit_tv);
        }

        public void setItems (Variable variable) {
            textView1.setText(variable.getName());
            textView2.setText(String.format("%.3f", variable.getValue()));
            textView3.setText(variable.getUnit());
        }
    }
}

Result class

public class Result extends AppCompatActivity {

    public ArrayList<Variable> rList = new ArrayList<>();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_result);

        Intent intent = getIntent();
        String tag = intent.getExtras().getString("tag");

        if (tag.equals("serie")) {
            SerieActivity serieActivity = new SerieActivity();
            rList = serieActivity.mList;
        }

        RecyclerView recyclerView = findViewById(R.id.result_rv);
        RVResultAdapter rvResultAdapter = new RVResultAdapter(this, rList);
        recyclerView.setAdapter(rvResultAdapter);
        recyclerView.setHasFixedSize(true);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));
        rvResultAdapter.notifyDataSetChanged();
    }
}

My problem is with the RecyclerView in Result. It shows the blue "end of content" things when I scroll up and down, so I guess the RecyclerView is there, but doesn't get any data. Any help is greatly appreciated. I am quite new to Android and Java programming, so I guess it must be a dumb thing that I just don't see.

Answer 1

just set the recyclerview code like this first initialize adapter then set layout manager and then set to adapter to recyclerview.

recyclerView = (RecyclerView) findViewById(R.id.recycler_view);

    mAdapter = new MoviesAdapter(movieList);
    RecyclerView.LayoutManager mLayoutManager = new LinearLayoutManager(getApplicationContext());
    recyclerView.setLayoutManager(mLayoutManager);
    recyclerView.setItemAnimator(new DefaultItemAnimator());
    recyclerView.setAdapter(mAdapter);

    prepareMovieData();

Answer 2

So you calling SerieActivity constructor in Results activity and execute populateList() inside onCreate(). You shouldn't create activities in this way because onCreate() will be never called. Instead of this you should pass data using putExtra and use Parcelable interface.

Answer 3

What are you doing dude. How can you get list from a new object of SerieActivity.class?

    if (tag.equals("serie")) {
        SerieActivity serieActivity = new SerieActivity();
        rList = serieActivity.mList;
    }

This is totally wrong way. If you want to pass list between activities. You can use parcelable methods putExtra and getExtra.

Assuming that your List is a list of strings make data an ArrayList<String> and use intent.putStringArrayListExtra("data", data)

Here is a skeleton of the code you need:

First you need to create a Parcelable object class, see the example

public class Student implements Parcelable {

        int id;
        String name;

        public Student(int id, String name) {
            this.id = id;
            this.name = name;

        }

        public int getId() {
            return id;
        }

        public String getName() {
            return name;
        }


        @Override
        public int describeContents() {
            // TODO Auto-generated method stub
            return 0;
        }

        @Override
        public void writeToParcel(Parcel dest, int arg1) {
            // TODO Auto-generated method stub
            dest.writeInt(id);
            dest.writeString(name);
        }

        public Student(Parcel in) {
            id = in.readInt();
            name = in.readString();
        }

        public static final Parcelable.Creator<Student> CREATOR = new Parcelable.Creator<Student>() {
            public Student createFromParcel(Parcel in) {
                return new Student(in);
            }

            public Student[] newArray(int size) {
                return new Student[size];
            }
        };
    }

And the list

ArrayList<Student> arraylist = new ArrayList<Student>();

Code from Calling activity

Intent intent = new Intent(this, SecondActivity.class);
Bundle bundle = new Bundle();
bundle.putParcelableArrayList("mylist", arraylist);
intent.putExtras(bundle);       
this.startActivity(intent);

Code on called activity

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_second);   

    Bundle bundle = getIntent().getExtras();
    ArrayList<Student> arraylist = bundle.getParcelableArrayList("mylist");
}