ScrollManager.java

package me.qixingchen.mdbilibili.view;

import android.animation.Animator;
import android.animation.ObjectAnimator;
import android.support.v7.widget.RecyclerView;
import android.view.View;
import android.view.ViewGroup;
import android.view.animation.AccelerateInterpolator;
import android.view.animation.DecelerateInterpolator;
import android.view.animation.Interpolator;

import java.util.HashMap;

/**
 * Created by Farble on 2015/6/21 15.
 */
public class ScrollManager extends RecyclerView.OnScrollListener {
    private static final String TAG = "ScrollManager";
    private static final int MIN_SCROLL_TO_HIDE = 10;
    private boolean hidden;
    private int accummulatedDy;
    private int totalDy;
    private int initialOffset;
    private HashMap<View, Direction> viewsToHide = new HashMap<>();

    public enum Direction {UP, DOWN}

    public ScrollManager() {
    }

    public void attach(RecyclerView recyclerView) {
        recyclerView.addOnScrollListener(this);
    }

    public void addView(View view, Direction direction) {
        viewsToHide.put(view, direction);
    }

    public void setInitialOffset(int initialOffset) {
        this.initialOffset = initialOffset;
    }

    @Override public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
        totalDy += dy;

        if (totalDy < initialOffset) {
            return;
        }

        if (dy > 0) {
            accummulatedDy = accummulatedDy > 0 ? accummulatedDy + dy : dy;
            if (accummulatedDy > MIN_SCROLL_TO_HIDE) {
                hideViews();
            }
        } else if (dy < 0) {
            accummulatedDy = accummulatedDy < 0 ? accummulatedDy + dy : dy;
            if (accummulatedDy < -MIN_SCROLL_TO_HIDE) {
                showViews();
            }
        }
    }

    public void hideViews() {
        if (!hidden) {
            hidden = true;
            for (View view : viewsToHide.keySet()) {
                hideView(view, viewsToHide.get(view));
            }
        }
    }

    private void showViews() {
        if (hidden) {
            hidden = false;
            for (View view : viewsToHide.keySet()) {
                showView(view);
            }
        }
    }

    private void hideView(View view, Direction direction) {
        int height = calculateTranslation(view);
        int translateY = direction == Direction.UP ? -height : height;
        runTranslateAnimation(view, translateY, new AccelerateInterpolator(3));
    }

    /**
     * Takes height + margins
     * @param view View to translate
     * @return translation in pixels
     */
    private int calculateTranslation(View view) {
        int height = view.getHeight();

        ViewGroup.MarginLayoutParams params = (ViewGroup.MarginLayoutParams) view.getLayoutParams();
        int margins = params.topMargin + params.bottomMargin;

        return height + margins;
    }

    private void showView(View view) {
        runTranslateAnimation(view, 0, new DecelerateInterpolator(3));
    }

    private void runTranslateAnimation(View view, int translateY, Interpolator interpolator) {
        Animator slideInAnimation = ObjectAnimator.ofFloat(view, "translationY", translateY);
        slideInAnimation.setDuration(view.getContext().getResources().getInteger(android.R.integer.config_mediumAnimTime));
        slideInAnimation.setInterpolator(interpolator);
        slideInAnimation.start();
    }
}