Hide floating button when collapsing toolbar is collapsed
<p>I have a coordinator layout containing a collapsing toolbar, a nestedscrollview and a floating button.
My floating button is placed at the bottom right end of the collapsing toolbar. <strong>I want the button to disappear when the collapsing toolbar is completely collapsed</strong>. And be visible in other situation.</p>

<p>My xml :</p>

<pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
&lt;android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    tools:context="fr.djey.secretapp.MainActivity"&gt;

    &lt;android.support.design.widget.AppBarLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:theme="@style/AppTheme.AppBarOverlay"
        android:id="@+id/appBar"&gt;

        &lt;android.support.design.widget.CollapsingToolbarLayout
            android:id="@+id/collapse_toolbar"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:layout_scrollFlags="scroll|exitUntilCollapsed"
            android:fitsSystemWindows="true"
            app:contentScrim="?attr/colorPrimary"
            app:expandedTitleMarginStart="48dp"
            app:expandedTitleMarginEnd="64dp"&gt;

            &lt;ImageView
                android:id="@+id/collapsing_image"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:fitsSystemWindows="true"
                app:layout_collapseMode="parallax"
                android:scaleType="centerCrop"
                android:src="@drawable/welcome"/&gt;

            &lt;android.support.v7.widget.Toolbar
                android:id="@+id/toolbar"
                android:layout_width="match_parent"
                android:layout_height="?attr/actionBarSize"
                app:popupTheme="@style/ThemeOverlay.AppCompat.Light"
                app:layout_collapseMode="pin"/&gt;

        &lt;/android.support.design.widget.CollapsingToolbarLayout&gt;

    &lt;/android.support.design.widget.AppBarLayout&gt;

    &lt;android.support.v4.widget.NestedScrollView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        xmlns:tools="http://schemas.android.com/tools"
        android:layout_gravity="fill_vertical"
        app:layout_behavior="@string/appbar_scrolling_view_behavior"
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"&gt;

        &lt;FrameLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:id="@+id/content_frame"&gt;

        &lt;/FrameLayout&gt;

    &lt;/android.support.v4.widget.NestedScrollView&gt;

    &lt;android.support.design.widget.FloatingActionButton
        android:id="@+id/fab"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="-60dp"
        android:layout_marginRight="16dp"
        android:src="@android:drawable/ic_dialog_email"
        app:layout_anchor="@id/collapse_toolbar"
        app:layout_anchorGravity="bottom|right|end" /&gt;

&lt;/android.support.design.widget.CoordinatorLayout&gt;
</code></pre>

<p>Is it possible and how?</p>