RecyclerViewScrollHelper

RecyclerViewScrollHelper

import android.support.annotation.FloatRange;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.view.View;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * @author puke
 * @version 2019/8/15
 */
public class RecyclerViewScrollHelper {

    public static final int DEFAULT_VALVE = DisplayUtils.dp2px(50);

    private final AtomContainer atomContainer;

    public interface OnScrollProgressListener {
        void onScrollProgress(@FloatRange(from = 0, to = 1) float progress);
    }

    public RecyclerViewScrollHelper(RecyclerView recyclerView) {
        if (recyclerView == null) {
            throw new IllegalArgumentException("The RecyclerView must not be null.");
        }
        this.atomContainer = new AtomContainer();
        recyclerView.addOnScrollListener(new ScrollListener());
    }

    public static NoRepeatScrollProgressListener unRepeatListener(OnScrollProgressListener progressListener) {
        return new NoRepeatScrollProgressListener(progressListener);
    }

    public void addListener(OnScrollProgressListener progressListener) {
        addListener(DEFAULT_VALVE, progressListener);
    }

    public void addListener(int scrollValve, OnScrollProgressListener progressListener) {
        if (scrollValve <= 0) {
            throw new IllegalArgumentException("The scroll valve must be positive.");
        }
        atomContainer.addListener(scrollValve, progressListener);
    }

    public void removeListener(OnScrollProgressListener progressListener) {
        atomContainer.removeListener(progressListener);
    }

    public void removeAllListeners() {
        atomContainer.removeAllListeners();
    }

    private class ScrollListener extends RecyclerView.OnScrollListener {
        @Override
        public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
            if (!(recyclerView.getLayoutManager() instanceof LinearLayoutManager)) {
                throw new UnsupportedOperationException("Current layout manager is not supported");
            }
            LinearLayoutManager layoutManager = (LinearLayoutManager) recyclerView.getLayoutManager();
            int position = layoutManager.findFirstVisibleItemPosition();

            for (OnScrollProgressListener listener : atomContainer.listeners) {
                final float progress;
                if (position == 0) {
                    Integer valve = atomContainer.listener2Valve.get(listener);
                    View firstVisibleChildView = layoutManager.findViewByPosition(position);
                    progress = -firstVisibleChildView.getTop() / (float) valve;
                } else {
                    progress = 1;
                }
                listener.onScrollProgress(formatProgress(progress));
            }
        }

        private float formatProgress(float progress) {
            if (progress < 0) {
                progress = 0;
            } else if (progress > 1) {
                progress = 1;
            }
            return progress;
        }
    }

    public static class NoRepeatScrollProgressListener implements OnScrollProgressListener {
        private final OnScrollProgressListener progressListener;
        private float lastProgress = -1;

        public NoRepeatScrollProgressListener(OnScrollProgressListener progressListener) {
            this.progressListener = progressListener;
        }

        @Override
        public void onScrollProgress(float progress) {
            if (lastProgress != progress && progressListener != null) {
                progressListener.onScrollProgress(progress);
            }
            this.lastProgress = progress;
        }
    }

    /* 原子容器, 保证 listeners 和 listener2Valve 的原子性; 外部只做读操作, 写操作统一由该类包装 */
    private static class AtomContainer {
        final List<OnScrollProgressListener> listeners;
        final Map<OnScrollProgressListener, Integer> listener2Valve;

        AtomContainer() {
            this.listeners = new ArrayList<>();
            this.listener2Valve = new HashMap<>();
        }

        void addListener(int scrollValve, OnScrollProgressListener progressListener) {
            if (progressListener != null && !listeners.contains(progressListener)) {
                listener2Valve.put(progressListener, scrollValve);
                listeners.add(progressListener);
            }
        }

        void removeListener(OnScrollProgressListener progressListener) {
            if (progressListener != null && listeners.contains(progressListener)) {
                listeners.remove(progressListener);
                listener2Valve.remove(progressListener);
            }
        }

        void removeAllListeners() {
            listeners.clear();
            listener2Valve.clear();
        }
    }

}