EndlessRecyclerOnScrollListener.java

/*
 * Copyright 2015, Tanmay Parikh
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.tanmay.blip.views;

import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.StaggeredGridLayoutManager;

/**
 * Created By ssins
 * GitHub: https://github.com/ssinss
 * Original Gist: https://gist.github.com/ssinss/e06f12ef66c51252563e
 */
public abstract class EndlessRecyclerOnScrollListener extends RecyclerView.OnScrollListener {
    public static String TAG = EndlessRecyclerOnScrollListener.class.getSimpleName();
    int firstVisibleItem, visibleItemCount, totalItemCount;
    private int previousTotal = 0; // The total number of items in the dataset after the last load
    private boolean loading = true; // True if we are still waiting for the last set of data to load.
    private int visibleThreshold = 4; // The minimum amount of items to have below your current scroll position before loading more.
    private int current_page = 1;

    private StaggeredGridLayoutManager mGridLayoutManager;

    public EndlessRecyclerOnScrollListener(StaggeredGridLayoutManager gridLayoutManager) {
        this.mGridLayoutManager = gridLayoutManager;
    }

    @Override
    public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
        super.onScrolled(recyclerView, dx, dy);

        visibleItemCount = recyclerView.getChildCount();
        totalItemCount = mGridLayoutManager.getItemCount();
        int[] items = new int[3];
        mGridLayoutManager.findFirstVisibleItemPositions(items);
        firstVisibleItem = items[0];

        if (loading) {
            if (totalItemCount > previousTotal) {
                loading = false;
                previousTotal = totalItemCount;
            }
        }
        if (!loading && (totalItemCount - visibleItemCount)
                <= (firstVisibleItem + visibleThreshold)) {
            // End has been reached

            // Do something
            current_page++;

            onLoadMore(current_page);

            loading = true;
        }
    }

    public abstract void onLoadMore(int current_page);
}