Implement Endless Scroll with RecyclerView

Implementation Idea

1. Distinguish different items you can define base Item class like this

    public abstract class ListItem {
        public final Type mType;
        protected ListItem(Type type){
            mType = type;
        }
        public int typeToInteger(){
            return mType.toInteger();
        }
        enum Type{
            NORMAL(0), PROGRESS(1);
            private int mOrder;
   
            Type(int type){
                mOrder = type;
            }
   
            public int toInteger(){
                return mOrder;
            }
        }
    }
   

2. Write RecyclerView Adapter

    public class MyAdapter extends RecyclerView.Adapter<MyAdapter.MyViewHolder>{
        private final List<ListItem> mDataSet;
        private final RecyclerView mRecyclerView;
   
        public MyAdapter(List<ListItem> dataSet, RecyclerView recyclerView){
            mDataSet = dataSet;
            mRecyclerView = recyclerView;
        }
   
        @Override
        public int getItemViewType(int position) {
            ListItem item = mDataSet.get(position);
            return item.mType.toInteger();
        }
   
        @Override
        public int getItemCount() {
            return mDataSet.size();
        }
   
        public static class MyViewHolder extends RecyclerView.ViewHolder{
            public final ListItem.Type mType;
            public MyViewHolder(View v, ListItem.Type type){
                super(v);
                mType = type;
            }
        }
    }
   

   the ListItem.Type will be used useful to distinguish between them.

3. Now Inheritance class MyViewHolder and class ListItem

   • Items

       public class ProgressItem extends ListItem{
           public ProgressItem(){
               super(Type.PROGRESS);
           }
       }
     

       public class NormalItem extends ListItem{
           private String text;
           public NormalItem(String data){
               super(Type.NORMAL);
               text = data;
           }
           public String getText(){
               return text;
           }
       }
     

   • ViewHolders
     The MyAdapter can use these ViewHolder for the onCreateViewHolder.

       public class ProgressViewHolder extends MyAdapter.MyViewHolder{
           public ProgressViewHolder(View v){
               super(v, ListItem.Type.PROGRESS);
           }
       }
     

       public class NormalViewHolder extends MyAdapter.MyViewHolder{
           public final TextView mTextView;
     
           public NormalViewHolder(View v) {
               super(v, ListItem.Type.NORMAL);
               mTextView = (TextView) v.findViewById(R.id.txt_field);
           }
       }
     

4. Override RecyclerView.Adapter’s methods (class MyAdapter)

    @NonNull
    @Override
    public MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View v;
        if(viewType == ListItem.Type.NORMAL.toInteger()){
            v = LayoutInflater.from(parent.getContext())
                    .inflate(R.layout.recycler_item, parent, false);
            return new NormalViewHolder(v);
        }
        else{//progress
            v = LayoutInflater.from(parent.getContext())
                    .inflate(R.layout.progress, parent, false);
            return new ProgressViewHolder(v);
        }
    }
   
    @Override
    public void onBindViewHolder(@NonNull MyViewHolder holder, int position) {
        if(holder.mType == ListItem.Type.NORMAL){
            NormalItem tmp = (NormalItem) mDataSet.get(position);
            ((NormalViewHolder) holder).mTextView.setText(tmp.getText());
        }
    }
   
    @Override
    public int getItemViewType(int position) {
        ListItem item = mDataSet.get(position);
        return item.mType.toInteger();
    }
   
    @Override
    public int getItemCount() {
        return mDataSet.size();
    }
   

   Now, you can understand why the ListItem.Type is needed. recyclerView.Adapter provides the getItemViewType so that we can distinguish between the ListItems. When RecyclerView creates a new View for ListItem, the Adapter can load different layouts depends on ListItem.type In this example, I used if-else cause there are only two different kinds of ListItem.

5. Finally, you can use it!
   for display progress bar

    private void setProgress(){
        mAdapter.addItem(new ProgressItem());
        mAdapter.notifyDataSetChanged();
    }
   

   you can add RecyclerView.OnScrollListener
   reference_stack_over_flow

    recyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
        @Override
        public void onScrollStateChanged(@NonNull RecyclerView recyclerView, int newState) {
            super.onScrollStateChanged(recyclerView, newState);
            if(!recyclerView.canScrollVertically(1) && newState == RecyclerView.SCROLL_STATE_IDLE){
                doTask();
            }
        }
    });
   

   the doTask() is AsyncTask for load more data from the source.