Collapsing toolbar android

Collapsing Tool Bar

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true">
    <android.support.design.widget.AppBarLayout
        android:id="@+id/app_bar"
        android:layout_height="250dp"
        android:layout_width="match_parent"
        android:fitsSystemWindows="true"
        android:background="@color/transparent"
        >
        <android.support.design.widget.CollapsingToolbarLayout
            android:id="@+id/ctFullStory"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:contentScrim="@android:color/white"
            android:fitsSystemWindows="true"
            app:layout_scrollFlags="scroll|exitUntilCollapsed"
            >
            <ImageView
                android:src="@mipmap/ic_launcher"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:id="@+id/ivFullStory"
                android:fitsSystemWindows="true"
                app:layout_collapseMode="parallax"
                android:scaleType="centerCrop"
                />
            <android.support.v7.widget.Toolbar
                android:id="@+id/toolbar"
                android:layout_width="match_parent"
                android:layout_height="?attr/actionBarSize"
                android:fitsSystemWindows="true"
                app:layout_collapseMode="pin"
                />
        </android.support.design.widget.CollapsingToolbarLayout>
    </android.support.design.widget.AppBarLayout>
    <include
        layout="@layout/full_story_webview"></include>
</android.support.design.widget.CoordinatorLayout>