FABMixedScrollBehavior.java

import android.content.Context;
import android.support.design.widget.AppBarLayout;
import android.support.design.widget.CoordinatorLayout;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v4.view.ViewCompat;
import android.util.AttributeSet;
import android.view.View;

import java.util.List;
/**
 * @author Polyterative
 * @version 3
 * as a part of "Abit" project
 * The code works by magic, with help by
 * @see <a href="https://github.com/cstew">Chris Stewart</a>
 * and
 * @see <a href="https://lab.getbase.com/introduction-to-coordinator-layout-on-android/">Grzesiek-Gajewski</a>
 * and
 * Google's codebase
 */
public class FABScrollBehavior extends CoordinatorLayout.Behavior<FloatingActionButton> {
    private int toolbarHeight;

    public FABScrollBehavior(Context context, AttributeSet attrs) {
        super(context, attrs);
        this.toolbarHeight = getToolbarHeight(context);
    }

    @Override
    public boolean layoutDependsOn(CoordinatorLayout parent, FloatingActionButton fab, View dependency) {
	    if (dependency instanceof AppBarLayout) {
		    return true;
	    } else return dependency instanceof Snackbar.SnackbarLayout;
    }

	/**
	 * The method decides which behaviour apply through dependency intanceof checking
	 *
	 * @param parent
	 * @param fab
	 * @param dependency
	 * @return true if fab was changed in size/moved
	 */
	@Override
	public boolean onDependentViewChanged(CoordinatorLayout parent, FloatingActionButton fab, View dependency) {

	    if (dependency instanceof AppBarLayout) {
		    onAppBarLayoutHide(fab, dependency);
	    } else if (dependency instanceof Snackbar.SnackbarLayout) {
		    onSnackBarScale(parent, fab, dependency);
//		    onSnackBarHide(parent, fab, dependency);
//		    onSnackBarRotate(parent, fab, dependency);

	    }
		return true;

	}

	/**
	 * Alternative SnackBar behavior
	 *
	 * @param parent
	 * @param fab
	 * @param dependency
	 */
	private void onSnackBarRotate(CoordinatorLayout parent, FloatingActionButton fab, View dependency) {
		float translationY = getFabTranslationYForSnackbar(parent, fab);
		float percentComplete = -translationY / dependency.getHeight();
		fab.setRotation(-90 * percentComplete);
		fab.setTranslationY(translationY);
	}

	/**
	 * Alternative behavior
	 *
	 * @param parent
	 * @param fab
	 * @param dependency
	 */
	private void onSnackBarHide(CoordinatorLayout parent, FloatingActionButton fab, View dependency) {
		float translationY = Math.min(0, dependency.getTranslationY() - dependency.getHeight());
		fab.setTranslationY(translationY);

	}

	/**
	 * Main snack movement, coherent with AppBarLayout's
	 *
	 * @param parent
	 * @param fab
	 * @param dependency
	 */
	private void onSnackBarScale(CoordinatorLayout parent, FloatingActionButton fab, View dependency) {

		float translationY = getFabTranslationYForSnackbar(parent, fab);
		float percentComplete = -translationY / dependency.getHeight();
		float scaleFactor = 1 - percentComplete;

		fab.setScaleX(scaleFactor);
		fab.setScaleY(scaleFactor);
	}

	/**
	 * Main behavior on on AppBarLayout movement
	 * @param fab
	 * @param dependency
	 */
	private void onAppBarLayoutHide(FloatingActionButton fab, View dependency) {
		CoordinatorLayout.LayoutParams lp = (CoordinatorLayout.LayoutParams) fab.getLayoutParams();
		int fabBottomMargin = lp.bottomMargin;
		int distanceToScroll = fab.getHeight() + fabBottomMargin;
		float ratio = dependency.getY() / (float) toolbarHeight;
		fab.setTranslationY(-distanceToScroll * ratio);
	}

	/**
	 * Utility method
	 * @param parent
	 * @param fab
	 * @return
	 */
	private float getFabTranslationYForSnackbar(CoordinatorLayout parent,
	                                            FloatingActionButton fab) {
		float minOffset = 0;
		final List<View> dependencies = parent.getDependencies(fab);
		for (int i = 0, z = dependencies.size(); i < z; i++) {
			final View view = dependencies.get(i);
			if (view instanceof Snackbar.SnackbarLayout && parent.doViewsOverlap(fab, view)) {
				minOffset = Math.min(minOffset,
						ViewCompat.getTranslationY(view) - view.getHeight());
			}
		}

		return minOffset;
	}
	
	public static int getToolbarHeight(Context context) {
			//for behavior, utility class
			final TypedArray styledAttributes = context.getTheme().obtainStyledAttributes(
					new int[]{R.attr.actionBarSize});
			int toolbarHeight = (int) styledAttributes.getDimension(0, 0);
			styledAttributes.recycle();

			return toolbarHeight;
		}

}