frameworks_base/packages/CarSystemUI/res/layout/car_navigation_bar.xml

<?xml version="1.0" encoding="utf-8"?>
<!--
  ~ Copyright (C) 2018 The Android Open Source Project
  ~
  ~ Licensed under the Apache License, Version 2.0 (the "License");
  ~ you may not use this file except in compliance with the License.
  ~ You may obtain a copy of the License at
  ~
  ~      http://www.apache.org/licenses/LICENSE-2.0
  ~
  ~ Unless required by applicable law or agreed to in writing, software
  ~ distributed under the License is distributed on an "AS IS" BASIS,
  ~ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  ~ See the License for the specific language governing permissions and
  ~ limitations under the License
  -->

<com.android.systemui.car.navigationbar.CarNavigationBarView
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:systemui="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@drawable/system_bar_background"
    android:orientation="vertical">
    <!--The 20dp padding is the difference between the background selected icon size and the ripple
        that was chosen, thus it's a hack to make it look pretty and not an official margin value-->
    <LinearLayout
        android:id="@id/nav_buttons"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:paddingStart="20dp"
        android:paddingEnd="20dp"
        android:gravity="center">

        <com.android.systemui.car.navigationbar.CarNavigationButton
            android:id="@+id/home"
            style="@style/NavigationBarButton"
            systemui:componentNames="com.android.car.carlauncher/.CarLauncher"
            systemui:icon="@drawable/car_ic_overview"
            systemui:intent="intent:#Intent;action=android.intent.action.MAIN;category=android.intent.category.HOME;launchFlags=0x14000000;end"
            systemui:selectedIcon="@drawable/car_ic_overview_selected"
            systemui:highlightWhenSelected="true"
        />

        <Space
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"/>

        <com.android.systemui.car.navigationbar.CarNavigationButton
            android:id="@+id/maps_nav"
            style="@style/NavigationBarButton"
            systemui:categories="android.intent.category.APP_MAPS"
            systemui:icon="@drawable/car_ic_navigation"
            systemui:intent="intent:#Intent;action=android.intent.action.MAIN;category=android.intent.category.APP_MAPS;launchFlags=0x14000000;end"
            systemui:selectedIcon="@drawable/car_ic_navigation_selected"
            systemui:highlightWhenSelected="true"
        />

        <Space
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"/>

        <com.android.systemui.car.navigationbar.CarNavigationButton
            android:id="@+id/music_nav"
            style="@style/NavigationBarButton"
            systemui:categories="android.intent.category.APP_MUSIC"
            systemui:icon="@drawable/car_ic_music"
            systemui:intent="intent:#Intent;action=android.car.intent.action.MEDIA_TEMPLATE;launchFlags=0x10000000;end"
            systemui:packages="com.android.car.media"
            systemui:selectedIcon="@drawable/car_ic_music_selected"
            systemui:highlightWhenSelected="true"
        />

        <Space
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"/>

        <com.android.systemui.car.navigationbar.CarNavigationButton
            android:id="@+id/phone_nav"
            style="@style/NavigationBarButton"
            systemui:icon="@drawable/car_ic_phone"
            systemui:intent="intent:#Intent;action=android.intent.action.MAIN;category=android.intent.category.LAUNCHER;package=com.android.car.dialer;launchFlags=0x10000000;end"
            systemui:packages="com.android.car.dialer"
            systemui:selectedIcon="@drawable/car_ic_phone_selected"
            systemui:highlightWhenSelected="true"
        />

        <Space
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"/>

        <com.android.systemui.car.navigationbar.CarNavigationButton
            android:id="@+id/grid_nav"
            style="@style/NavigationBarButton"
            systemui:componentNames="com.android.car.carlauncher/.AppGridActivity"
            systemui:icon="@drawable/car_ic_apps"
            systemui:intent="intent:#Intent;component=com.android.car.carlauncher/.AppGridActivity;launchFlags=0x24000000;end"
            systemui:selectedIcon="@drawable/car_ic_apps_selected"
            systemui:highlightWhenSelected="true"
        />

        <Space
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"/>

        <com.android.systemui.car.navigationbar.CarNavigationButton
            android:id="@+id/notifications"
            style="@style/NavigationBarButton"
            systemui:icon="@drawable/car_ic_notification"
            systemui:longIntent="intent:#Intent;component=com.android.car.bugreport/.BugReportActivity;end"
        />

        <Space
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"/>

        <com.android.systemui.car.navigationbar.AssitantButton
            android:id="@+id/assist"
            style="@style/NavigationBarButton"
            systemui:icon="@drawable/ic_mic_white"
        />

    </LinearLayout>

    <LinearLayout
        android:id="@+id/lock_screen_nav_buttons"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:paddingStart="@dimen/car_keyline_1"
        android:paddingEnd="@dimen/car_keyline_1"
        android:gravity="center"
        android:visibility="gone"
    />

</com.android.systemui.car.navigationbar.CarNavigationBarView>