BinderRecyclerViewAdapter.java

import android.support.v7.widget.RecyclerView;
import android.util.SparseArray;
import android.view.LayoutInflater;
import android.view.ViewGroup;

import java.util.Collections;
import java.util.List;
import java.util.Objects;

public abstract class BinderRecyclerViewAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {
    private final SparseArray<Binder<?, ?>> binders = new SparseArray<>();
    protected List<Item<?>> items = Collections.emptyList();

    @Override
    public final RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        final Binder<?, ?> binder = binders.get(viewType);
        return binder.createViewHolder(LayoutInflater.from(parent.getContext()), parent, viewType);
    }

    @Override
    @SuppressWarnings({"unchecked", "rawtypes"})
    public final void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
        final Item<?> item = items.get(position);
        final Binder binder = binders.get(item.getType());
        binder.bindViewHolder(holder, item.getPayload());
    }

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

    @Override
    public final long getItemId(int position) {
        return items.get(position).getId();
    }

    @Override
    public final int getItemViewType(int position) {
        return items.get(position).getType();
    }

    @SuppressWarnings("unchecked")
    public final <T> T getItemPayload(int position) {
        return (T) items.get(position).getPayload();
    }

    protected final void registerBinder(int type, Binder<?, ?> binder) {
        if (binders.get(type) != null) {
            throw new IllegalStateException("Binder for type " + type + " is already registered");
        }
        binders.append(type, Objects.requireNonNull(binder));
    }

    public interface Binder<T, VH extends RecyclerView.ViewHolder> {
        VH createViewHolder(LayoutInflater inflater, ViewGroup parent, int viewType);

        void bindViewHolder(VH holder, T value);
    }

    public static final class StaticViewBinder implements Binder<Void, StaticViewBinder.ViewHolder> {
        private final int layoutId;

        public StaticViewBinder(@LayoutRes int layoutId) {
            this.layoutId = layoutId;
        }

        @Override
        public ViewHolder createViewHolder(LayoutInflater inflater, ViewGroup parent, int viewType) {
            final View view = inflater.inflate(layoutId, parent, false);
            return new ViewHolder(view);
        }

        @Override
        public void bindViewHolder(ViewHolder holder, Void unused) {
        }

        static class ViewHolder extends RecyclerView.ViewHolder {
            ViewHolder(View itemView) {
                super(itemView);
            }
        }
    }

    protected static final class Item<T> {
        private final long id;
        private final int type;
        private final T payload;

        public static <T> Item<T> create(int type, T payload) {
            return new Item<>(RecyclerView.NO_ID, type, payload);
        }

        public static <T> Item<T> create(long id, int type, T payload) {
            return new Item<>(id, type, payload);
        }

        private Item(long id, int type, T payload) {
            this.id = id;
            this.type = type;
            this.payload = payload;
        }

        public long getId() {
            return id;
        }

        public int getType() {
            return type;
        }

        public T getPayload() {
            return payload;
        }

        @Override
        public boolean equals(Object o) {
            if (this == o) return true;
            if (o == null || getClass() != o.getClass()) return false;
            final Item<?> other = (Item<?>) o;
            return id == other.id &&
                    type == other.type &&
                    Objects.equals(payload, other.payload);
        }

        @Override
        public int hashCode() {
            return Objects.hash(id, type, payload);
        }

        @Override
        public String toString() {
            return "Item{" +
                    "id=" + (id == RecyclerView.NO_ID ? "NO_ID" : Long.toString(id)) +
                    ", type=" + type +
                    ", payload=" + payload +
                    '}';
        }
    }
}