How can I implement a RecyclerView inside another RecyclerView's item

Question

I should implement a RecyclerView, its item contains a TextView and another inner horizontal RecyclerView.

I started it considering that the inner RecyclerView likes any other View. The issue happened when I tried to pass the context to the LinearLayoutManager() and the RecyclerView.setAdapter().

The issue is: I cannot pass the context, because I'm trying to pass it inside the first RecyclerView adapter

I cannot pass the context and don't know if this way is the optimal or if it will work at the end.

Here's my code:


public class TheFirstAdapter extends RecyclerView.Adapter<TheFirstAdapter.TheFirstViewHolder> {

    private Context context;
    private List<FirstItemModel> firstItemModelList;
    private List<SecondItemModel> secondItemModelList;
    SecondItemModel secondItemModel;
    TheSecondAdapter theSecondAdapter;

    public TheFirstAdapter(Context context, List<FirstItemModel> firstItemModel) {
        this.context = context;
        this.firstItemModelList = firstItemModelList;
    }

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

    @Override
    public void onBindViewHolder(@NonNull TheFirstViewHolder holder, int position) {

//there is an error in this line:
////java.lang.NullPointerException: Attempt to invoke interface method 'boolean java.util.List.add(java.lang.Object)' on a null object reference

//////the solution: secondItemModelList= new ArrayList<>(); 
            for (int i = 1; i < 5; i++) {
            secondItemModel = new AddRoutineRoutines("Morning", "#9697D6");
            secondItemModelList.add(secondItemModel);
        }

        FirstItemModel firstItemModel = firstItemModelList.get(position);
        holder.textView.setText(addRoutineItemModel.getFirstItemText());
        holder.theSecondRecyclerView.setLayoutManager(new LinearLayoutManager(context));
        TheSecondAdapter theSecondAdapter = new TheSecondAdapter(context, secondItemModelList);
        holder.theSecondRecyclerView.setAdapter();
    }

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

    class TheFirstViewHolder extends RecyclerView.ViewHolder {

        TextView textView;
        RecyclerView theSecondRecyclerView;

        public TheFirstViewHolder(@NonNull View itemView) {

            super(itemView);
            textView = itemView.findViewById(R.id.first_item_text);
            theSecondRecyclerView = itemView.findViewById(R.id.the_second_recycler_view);
        }
    }
}

Edit1: I passed the context but still there a problem I showed above.

Edit2: The problem was I didn't initialized the secondItemModelList.

*After discussions this code works:*


public class TheFirstAdapter extends RecyclerView.Adapter<TheFirstAdapter.TheFirstViewHolder> {

    private Context context;
    private List<FirstItemModel> firstItemModelList;
    private List<SecondItemModel> secondItemModelList;
    SecondItemModel secondItemModel;

    public TheFirstAdapter(Context context, List<FirstItemModel> firstItemModel) {
        this.context = context;
        this.firstItemModelList = firstItemModelList;
    }

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

    @Override
    public void onBindViewHolder(@NonNull TheFirstViewHolder holder, int position) {

        FirstItemModel firstItemModel = firstItemModelList.get(position);
        holder.textView.setText(addRoutineItemModel.getFirstItemText());
        holder.updateView(secondItemModelList);
    }

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

    class TheFirstViewHolder extends RecyclerView.ViewHolder {

        TextView textView;
        RecyclerView theSecondRecyclerView;

        public TheFirstViewHolder(@NonNull View itemView) {

            super(itemView);
            textView = itemView.findViewById(R.id.first_item_text);
            theSecondRecyclerView = itemView.findViewById(R.id.the_second_recycler_view);
        }

        public updateView(List<SecondItemModel> secondItemModelList) {
            secondItemModelList = new ArrayList<>();

            for (int i = 1; i < 5; i++) {
                secondItemModel = new SecondItemModel("Morning", "#9697D6");
                secondItemModelList.add(secondItemModel);
            }

            TheSecondAdapter theSecondAdapter = new TheSecondAdapter(context, secondItemModelList);
            LinearLayoutManager layoutManager
                    = new LinearLayoutManager(context, LinearLayoutManager.HORIZONTAL, false);
            theSecondRecyclerView.setLayoutManager(layoutManager);
            theSecondRecyclerView.setAdapter(theSecondAdapter);
        }
    }
}

`parse the context` do you mean **pass** the context? `The issue happened when I tried to parse the context` which issue? — Vladyslav Matviienko, Sep 16 '19 at 09:08
that does not answer my question: `The issue happened when I tried to parse the context` which issue? — Vladyslav Matviienko, Sep 16 '19 at 09:09
@VladyslavMatviienko the issue is: ```I cannot pass the context```, because I'm trying to pass it inside the first ```RecyclerView``` adapter — Abdurrahman Anas, Sep 16 '19 at 09:13
not quite clear what the problem is. RecyclerViews inside of a RecyclerView should not be any problem, i created a vertical list with recyclerView in which each row was a horizontal list (RecyclerView) of items. If passing the context is the problem, please show the code where you pass it and the error that happends when you do. — Joachim Haglund, Sep 16 '19 at 09:14
@AbdurrahmanAnas brother and coder you need to give clear and concise information atleast — Faizzy, Sep 16 '19 at 09:17
Please stop hiding the details. `//////////there is an error in this line` which error? — Vladyslav Matviienko, Sep 16 '19 at 10:17
@VladyslavMatviienko it's: ```java.lang.NullPointerException: Attempt to invoke interface method 'boolean java.util.List.add(java.lang.Object)' on a null object reference``` — Abdurrahman Anas, Sep 16 '19 at 10:21
`secondItemModelList` is null it says, you never initialize it. — Vladyslav Matviienko, Sep 16 '19 at 10:22
@VladyslavMatviienko Thanks alot! it works now, I initialized it inside ```onBindViewHolder()```. How can I make the inner recycler horizontal? and is this really a bad code? — Abdurrahman Anas, Sep 16 '19 at 10:30
yes, this is really a bad code. You can make it horizontal by using corresponding LayoutManager. — Vladyslav Matviienko, Sep 16 '19 at 10:48
Possible duplicate of [What is a NullPointerException, and how do I fix it?](https://stackoverflow.com/questions/218384/what-is-a-nullpointerexception-and-how-do-i-fix-it) — Vladyslav Matviienko, Sep 16 '19 at 10:48
you may look for nested recycler view here https://android.jlelse.eu/easily-adding-nested-recycler-view-in-android-a7e9f7f04047 — Faizzy, Sep 16 '19 at 11:17
@VladyslavMatviienko thanks, I followed your instructions and it works, Is this still a bad code? — Abdurrahman Anas, Sep 16 '19 at 11:24

Sinh Phan · Accepted Answer · 2019-09-17T02:24:05.957

-1

What is the context which you send to arg of constructor LinearLayoutManager? If I understand your issue. You are using context from parent. Please use itemView.context.

Update:

Your code is very bad.

Do not create adapter in the bindView method.
Do not set/remove data in the bindView method.
BindView only use for bind data for view. Only that.

ViewHolder should be like this:

class TheFirstViewHolder extends RecyclerView.ViewHolder {

        TextView textView;
        RecyclerView theSecondRecyclerView;
        TheFirstAdapter adapter;

        public TheFirstViewHolder(@NonNull View itemView) {

            super(itemView);
            textView = itemView.findViewById(R.id.first_item_text);
            theSecondRecyclerView = itemView.findViewById(R.id.the_second_recycler_view);
        }

        public void updateView(....) {
           //create new adapter if need.
           //set data for adapter if need
           ...
        }
    }

onBindViewHolder should be like this: holder.updateView(...)

edited Sep 17 '19 at 02:24

answered Sep 16 '19 at 10:09

Sinh Phan

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@AbdurrahmanAnas Your code is very bad. 1. Do not create adapter in the `bindView` method. 2. Do not set/remove data in the `bindView` method. 3. `BindView` only use for bind data for view. Only that. – Sinh Phan Sep 16 '19 at 10:22
this does not answer the question. Please don;t use `answer` for comments. – Vladyslav Matviienko Sep 16 '19 at 10:22
@VladyslavMatviienko Really? This issue by change adapter data in the `bindView` method and create new instance in there. Not only with context. – Sinh Phan Sep 16 '19 at 10:24
`I dont understand exactly your question.` you really don't. Don't try to answer before you are sure that you do. – Vladyslav Matviienko Sep 16 '19 at 10:26
Oh. Ok Thank @VladyslavMatviienko. I understand that. Let's me edit my answer – Sinh Phan Sep 16 '19 at 10:27
@PhanSinh thanks I followed your instructions and it works, Is this still a bad code? – Abdurrahman Anas Sep 16 '19 at 11:23

How can I implement a RecyclerView inside another RecyclerView's item

1 Answers1