How to create a simple divider in the new NavigationView?

All you need to do is define a group with an unique ID, I have checked the implementation if group has different id's it will create a divider.

Example menu, creating the separator:

<menu 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"    tools:context=".MainActivity">    <group android:id="@+id/grp1" android:checkableBehavior="single" >        <item            android:id="@+id/navigation_item_1"            android:checked="true"            android:icon="@drawable/ic_home"            android:title="@string/navigation_item_1" />    </group>    <group android:id="@+id/grp2" android:checkableBehavior="single" >        <item            android:id="@+id/navigation_item_2"            android:icon="@drawable/ic_home"            android:title="@string/navigation_item_2" />    </group></menu>

create a drawable drawer_item_bg.xml like this,

    <layer-list xmlns:android="http://schemas.android.com/apk/res/android">    <item>        <shape android:shape="rectangle" >            <solid android:color="#F4F4F4" />        </shape>    </item>    <item android:top="-2dp" android:right="-2dp" android:left="-2dp">        <shape>            <solid android:color="@android:color/transparent" />            <stroke                android:width="1dp"                android:color="#EAEAEA" />        </shape>        <!--        android:dashGap="10px"                android:dashWidth="10px"                -->    </item></layer-list>

and add it to NavigationView as app:itemBackground="@drawable/drawer_item_bg"

<android.support.design.widget.NavigationView        android:id="@+id/nav_view"        android:layout_width="wrap_content"        android:layout_height="match_parent"        android:background="#F4F4F4"        android:layout_gravity="start"        android:fitsSystemWindows="false"        app:menu="@menu/activity_main_drawer"        app:itemBackground="@drawable/drawer_item_bg"/>

and here we go...

You can add dividers easily by setting Menu Item Background via XML using app:itemBackground

<android.support.design.widget.NavigationView    android:id="@id/drawer_navigation_view"    android:layout_width="wrap_content"    android:layout_height="match_parent"    android:layout_gravity="start"    android:fitsSystemWindows="true"    app:menu="@menu/all_navigation_menu"    app:itemIconTint="@color/colorPrimary"    app:itemBackground="@drawable/bg_drawer_item"    android:background="@color/default_background"/>

And use LayerDrawable as the background. It preserves material design ripple overlay for clicks.

<?xml version="1.0" encoding="utf-8"?><layer-list xmlns:android="http://schemas.android.com/apk/res/android">    <item>        <shape android:shape="rectangle">            <solid android:color="@color/white"/>        </shape>    </item>    <item android:left="@dimen/activity_horizontal_margin">        <shape android:shape="rectangle">            <solid android:color="@color/divider"/>        </shape>    </item>    <item android:bottom="1dp">        <shape android:shape="rectangle">            <solid android:color="@color/white"/>        </shape>    </item></layer-list>

The result: