QuickReturnFooterBehavior.java

package com.example.widget;

import android.animation.Animator;
import android.content.Context;
import android.support.design.widget.CoordinatorLayout;
import android.support.v4.view.ViewCompat;
import android.support.v4.view.animation.FastOutSlowInInterpolator;
import android.util.AttributeSet;
import android.view.View;
import android.view.ViewPropertyAnimator;
import android.view.animation.Interpolator;


/**
 * CoordinatorLayout Behavior for a quick return footer
 * <p>
 * When a nested ScrollView is scrolled down, the quick return view will disappear.
 * When the ScrollView is scrolled back up, the quick return view will reappear.
 * <p>
 * Source: https://github.com/bherbst/QuickReturnFooterSample
 *
 * @author bherbst
 */
@SuppressWarnings("unused")
public class QuickReturnFooterBehavior extends CoordinatorLayout.Behavior<View>
{
	private static final Interpolator INTERPOLATOR = new FastOutSlowInInterpolator();

	private int mDySinceDirectionChange;
	private boolean mIsShowing;
	private boolean mIsHiding;


	public QuickReturnFooterBehavior(Context context, AttributeSet attrs)
	{
		super(context, attrs);
	}


	@Override
	public boolean onStartNestedScroll(CoordinatorLayout coordinatorLayout, View child, View directTargetChild, View target, int nestedScrollAxes)
	{
		return (nestedScrollAxes & ViewCompat.SCROLL_AXIS_VERTICAL) != 0;
	}


	@Override
	public void onNestedPreScroll(CoordinatorLayout coordinatorLayout, View child, View target, int dx, int dy, int[] consumed)
	{
		if(dy > 0 && mDySinceDirectionChange < 0 || dy < 0 && mDySinceDirectionChange > 0)
		{
			// We detected a direction change- cancel existing animations and reset our cumulative delta Y
			child.animate().cancel();
			mDySinceDirectionChange = 0;
		}

		mDySinceDirectionChange += dy;

		if(mDySinceDirectionChange > child.getHeight() && child.getVisibility() == View.VISIBLE && !mIsHiding)
		{
			hide(child);
		}
		else if(mDySinceDirectionChange < 0 && child.getVisibility() == View.GONE && !mIsShowing)
		{
			show(child);
		}
	}


	/**
	 * Hide the quick return view.
	 * <p>
	 * Animates hiding the view, with the view sliding down and out of the screen.
	 * After the view has disappeared, its visibility will change to GONE.
	 *
	 * @param view The quick return view
	 */
	private void hide(final View view)
	{
		mIsHiding = true;
		ViewPropertyAnimator animator = view.animate()
				.translationY(view.getHeight())
				.setInterpolator(INTERPOLATOR)
				.setDuration(200);

		animator.setListener(new Animator.AnimatorListener()
		{
			@Override
			public void onAnimationStart(Animator animator) {}


			@Override
			public void onAnimationEnd(Animator animator)
			{
				// Prevent drawing the View after it is gone
				mIsHiding = false;
				view.setVisibility(View.GONE);
			}


			@Override
			public void onAnimationCancel(Animator animator)
			{
				// Canceling a hide should show the view
				mIsHiding = false;
				if(!mIsShowing)
				{
					show(view);
				}
			}


			@Override
			public void onAnimationRepeat(Animator animator) {}
		});

		animator.start();
	}


	/**
	 * Show the quick return view.
	 * <p>
	 * Animates showing the view, with the view sliding up from the bottom of the screen.
	 * After the view has reappeared, its visibility will change to VISIBLE.
	 *
	 * @param view The quick return view
	 */
	private void show(final View view)
	{
		mIsShowing = true;
		ViewPropertyAnimator animator = view.animate()
				.translationY(0)
				.setInterpolator(INTERPOLATOR)
				.setDuration(200);

		animator.setListener(new Animator.AnimatorListener()
		{
			@Override
			public void onAnimationStart(Animator animator)
			{
				view.setVisibility(View.VISIBLE);
			}


			@Override
			public void onAnimationEnd(Animator animator)
			{
				mIsShowing = false;
			}


			@Override
			public void onAnimationCancel(Animator animator)
			{
				// Canceling a show should hide the view
				mIsShowing = false;
				if(!mIsHiding)
				{
					hide(view);
				}
			}


			@Override
			public void onAnimationRepeat(Animator animator) {}
		});

		animator.start();
	}
}