Android app can display one activity at once (it's changed recently but in your scenario it's still true). In your case you should inflate View or Fragment. Just put your layout or fragment inside NavigationView
:
<?xml version="1.0" encoding="utf-8"?>
<androidx.drawerlayout.widget.DrawerLayout 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:id="@+id/drawer_layout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
tools:openDrawer="start">
<include
layout="@layout/app_bar_main"
android:layout_width="match_parent"
android:layout_height="match_parent" />
<com.google.android.material.navigation.NavigationView
android:id="@+id/nav_view"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:layout_gravity="start"
android:fitsSystemWindows="true"
app:headerLayout="@layout/nav_header_main"
app:menu="@menu/activity_main_drawer">
<TextView
android:text="Custom View"
android:layout_gravity="center"
android:background="#ff0000"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
</com.google.android.material.navigation.NavigationView>
</androidx.drawerlayout.widget.DrawerLayout>
NavigationView
extends FrameLayout so if you will inflate menu it will overlap. Because of that you may want to delete:
app:headerLayout="@layout/nav_header_main"
app:menu="@menu/activity_main_drawer"
