FAB behavior that lets FAB scroll out towards the bottom in sync with AppBarLayout scrolling out towards the top

## AppBarBoundFabBehavior.java
/**
 * Behavior for FABs that does not support anchoring to AppBarLayout, but instead translates the FAB
 * out of the bottom in sync with the AppBarLayout collapsing towards the top.
 * <p>
 * Extends FloatingActionButton.Behavior to keep using the pre-Lollipop shadow padding offset.
 */
public class AppBarBoundFabBehavior extends FloatingActionButton.Behavior {

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


    @Override
    public boolean layoutDependsOn(CoordinatorLayout parent, FloatingActionButton child, View dependency) {
        if (dependency instanceof AppBarLayout) {
            ((AppBarLayout) dependency).addOnOffsetChangedListener(new FabOffsetter(parent, child));
        }
        return dependency instanceof AppBarLayout || super.layoutDependsOn(parent, child, dependency);
    }

    @Override
    public boolean onDependentViewChanged(CoordinatorLayout parent, FloatingActionButton fab, View dependency) {
        //noinspection SimplifiableIfStatement
        if (dependency instanceof AppBarLayout) {
            // if the dependency is an AppBarLayout, do not allow super to react on that
            // we don't want that behavior
            return true;
        }
        return super.onDependentViewChanged(parent, fab, dependency);
    }
  }

## FabOffsetter.java
public class FabOffsetter implements AppBarLayout.OnOffsetChangedListener {
    private final CoordinatorLayout parent;
    private final FloatingActionButton fab;

    public FabOffsetter(@NonNull CoordinatorLayout parent, @NonNull FloatingActionButton child) {
        this.parent = parent;
        this.fab = child;
    }

    @Override
    public void onOffsetChanged(AppBarLayout appBarLayout, int verticalOffset) {
      // fab should scroll out down in sync with the appBarLayout scrolling out up.
      // let's see how far along the way the appBarLayout is
      // (if displacementFraction == 0.0f then no displacement, appBar is fully expanded;
      //  if displacementFraction == 1.0f then full displacement, appBar is totally collapsed)
      float displacementFraction = -verticalOffset / (float) appBarLayout.getHeight();

      // need to separate translationY on the fab that comes from this behavior
      // and one that comes from other sources
      // translationY from this behavior is stored in a tag on the fab
      float translationYFromThis = coalesce((Float) fab.getTag(R.id.fab_translationY_from_AppBarBoundFabBehavior), 0f);

      // top position, accounting for translation not coming from this behavior
      float topUntranslatedFromThis = fab.getTop() + fab.getTranslationY() - translationYFromThis;

      // total length to displace by (from position uninfluenced by this behavior) for a full appBar collapse
      float fullDisplacement = parent.getBottom() - topUntranslatedFromThis;

      // calculate and store new value for displacement coming from this behavior
      float newTranslationYFromThis = fullDisplacement * displacementFraction;
      fab.setTag(R.id.fab_translationY_from_AppBarBoundFabBehavior, newTranslationYFromThis);

      // update translation value by difference found in this step
      fab.setTranslationY(newTranslationYFromThis - translationYFromThis + fab.getTranslationY());
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        OnOffsetChangedListener that = (OnOffsetChangedListener) o;

        return parent.equals(that.parent) && fab.equals(that.fab);

    }

    @Override
    public int hashCode() {
        int result = parent.hashCode();
        result = 31 * result + fab.hashCode();
        return result;
    }
}

## values.xml
<?xml version="1.0" encoding="utf-8"?>
<resources xmlns:tools="http://schemas.android.com/tools" tools:ignore="MissingTranslation">
  <item type="id" name="fab_translationY_from_AppBarBoundFabBehavior"/>
</resources>