BaseHeaderAdapter.java

package com.nilhcem.bblfr.ui;

import android.support.annotation.IntDef;
import android.support.v7.widget.RecyclerView;
import android.view.ViewGroup;

import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public abstract class BaseHeaderAdapter<H, I, HV extends BaseRecyclerViewHolder<H>, IV extends BaseRecyclerViewHolder<I>>
        extends RecyclerView.Adapter<BaseRecyclerViewHolder> {

    @IntDef({TYPE_ITEM, TYPE_HEADER})
    @Retention(RetentionPolicy.SOURCE)
    public @interface ViewType {
    }

    static final int TYPE_ITEM = 1;
    static final int TYPE_HEADER = 2;

    protected H mHeader;
    protected List<I> mItems = Collections.emptyList();
    boolean mHasHeader;

    @Override
    public BaseRecyclerViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        if (viewType == TYPE_ITEM) {
            return onCreateItemView(parent);
        } else if (viewType == TYPE_HEADER) {
            return onCreateHeaderView(parent);
        }
        throw new RuntimeException("There is no type that matches the type " + viewType + " + make sure your using types correctly");
    }

    @Override
    public void onBindViewHolder(BaseRecyclerViewHolder holder, int position) {
        if (isPositionHeader(position)) {
            onBindHeaderView((HV) holder, mHeader);
        } else {
            onBindItemView((IV) holder, mItems.get(position - (mHasHeader ? 1 : 0)));
            // "- 1" as we are taking header into account so all of our items are correctly positioned.
        }
    }

    @Override
    public int getItemCount() {
        if (mItems.isEmpty()) {
            // Empty view.
            return 0;
        }
        // Items + 1 header.
        return mItems.size() + (mHasHeader ? 1 : 0);
    }

    @Override
    @ViewType
    public int getItemViewType(int position) {
        if (isPositionHeader(position)) {
            return TYPE_HEADER;
        }
        return TYPE_ITEM;
    }

    public void updateItems(List<I> items) {
        updateItems(items, null);
    }

    public void updateItems(List<I> items, H headerData) {
        updateItems(items, headerData, headerData != null);
    }

    public void updateItems(List<I> items, H headerData, boolean hasHeader) {
        mHeader = headerData;
        mHasHeader = hasHeader;

        if (items == null) {
            mItems = Collections.emptyList();
        } else {
            mItems = new ArrayList<>(items);
        }
        notifyDataSetChanged();
    }

    private boolean isPositionHeader(int position) {
        return mHasHeader && position == 0;
    }

    protected abstract IV onCreateItemView(ViewGroup parent);

    protected HV onCreateHeaderView(ViewGroup parent) {
        return null;
    }

    protected void onBindItemView(IV view, I item) {
        view.bindData(item);
    }

    protected void onBindHeaderView(HV view, H header) {
        view.bindData(header);
    }
}