BottomNavigationBehavior.java

package com.bubblesoft.android.utils;

import android.animation.ValueAnimator;
import android.animation.ValueAnimator.AnimatorUpdateListener;
import android.content.Context;
import android.support.design.widget.CoordinatorLayout;
import android.support.design.widget.Snackbar;
import android.support.v4.view.ViewCompat;
import android.util.AttributeSet;
import android.view.Gravity;
import android.view.View;
import android.view.animation.DecelerateInterpolator;

public class BottomNavigationBehavior<V extends View>  extends CoordinatorLayout.Behavior<V> {

	// Code from Valentin Hinov converted from Kotlin 
	// https://android.jlelse.eu/scroll-your-bottom-navigation-view-away-with-10-lines-of-code-346f1ed40e9e
	
	private int lastStartedType;
	private ValueAnimator offsetAnimator;
	private boolean isSnappingEnabled = true; // set to false to disable snap support

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

	public BottomNavigationBehavior () {
		super();
	}
	
	public void setSnappingEnabled(boolean isEnabled) {
		isSnappingEnabled = isEnabled;
		lastStartedType = 0;
		if (offsetAnimator != null) {
			offsetAnimator.cancel();
			offsetAnimator = null;
		}
	}
	
	public void expand(CoordinatorLayout coordinatorLayout, V child) {
		
		int[] consumed = new int[2];
		
		boolean curIsSnappingEnabled = isSnappingEnabled;
		if(curIsSnappingEnabled) {
		  setSnappingEnabled(false);
		}
		
		onNestedPreScroll(coordinatorLayout, child, null, 0, -1000, consumed, ViewCompat.TYPE_TOUCH);
		
		if(curIsSnappingEnabled) {
		  setSnappingEnabled(true);
		}
	}
	
	@Override
	public boolean onStartNestedScroll(CoordinatorLayout coordinatorLayout, V child, View directTargetChild,
			View target, int axes, int type) {

		if (axes != ViewCompat.SCROLL_AXIS_VERTICAL)
			return false;

		lastStartedType = type;
		if(offsetAnimator!= null) {
			offsetAnimator.cancel();
		}
		
		return true;
	}
	
	@Override
	public void onStopNestedScroll(CoordinatorLayout coordinatorLayout, V child, View target, int type) {
		if (!isSnappingEnabled)
			return ;

		// add snap behaviour
		// Logic here borrowed from AppBarLayout onStopNestedScroll code
		
		if (lastStartedType == ViewCompat.TYPE_TOUCH || type == ViewCompat.TYPE_NON_TOUCH) {
			
			// find nearest seam
			float currTranslation = child.getTranslationY();
			float childHalfHeight = child.getHeight() * 0.5f;

			if (currTranslation >= childHalfHeight) {
				animateBarVisibility(child, false); // translate down
			} else {  
				animateBarVisibility(child, true); // translate up
			}

		}
	}

	@Override
	public void onNestedPreScroll (CoordinatorLayout coordinatorLayout, 
			V child, 
			View target, 
			int dx, 
			int dy, 
			int[] consumed, 
			int type) {

		super.onNestedPreScroll(coordinatorLayout, child, target, dx, dy, consumed, type);
		child.setTranslationY(Math.max(0f, Math.min(child.getHeight(), child.getTranslationY() + dy)));
	}


	@Override 
	public boolean layoutDependsOn(CoordinatorLayout parent, V child, View dependency) {
		if(dependency instanceof Snackbar.SnackbarLayout) {
			updateSnackbar(child, (Snackbar.SnackbarLayout)dependency);
		}

		return super.layoutDependsOn(parent, child, dependency);
	}


	private void updateSnackbar(View child, Snackbar.SnackbarLayout snackbarLayout) {
		if(snackbarLayout.getLayoutParams() instanceof CoordinatorLayout.LayoutParams) {
			CoordinatorLayout.LayoutParams params = (CoordinatorLayout.LayoutParams)snackbarLayout.getLayoutParams();

			params.setAnchorId(child.getId());
			params.anchorGravity = Gravity.CENTER_HORIZONTAL;
			params.gravity = Gravity.CENTER_HORIZONTAL;
			snackbarLayout.setLayoutParams(params);
		}
	}
	

	private void animateBarVisibility(final View child, boolean isVisible) {
		if (offsetAnimator == null) {
			offsetAnimator = new ValueAnimator();
			offsetAnimator.setInterpolator(new DecelerateInterpolator());
			offsetAnimator.setDuration(150L);
			offsetAnimator.addUpdateListener(new AnimatorUpdateListener() {
				@Override
				public void onAnimationUpdate(ValueAnimator animation) {
					child.setTranslationY((float)animation.getAnimatedValue());
				}
			});
		} else {
			offsetAnimator.cancel();
		}

		float targetTranslation = isVisible ? 0f : child.getHeight();
		offsetAnimator.setFloatValues(child.getTranslationY(), targetTranslation);
		offsetAnimator.start();
	}
}