Introduction to AAOS System UI Customization

Android Automotive OS (AAOS) provides a powerful, open-source platform for in-vehicle infotainment systems. While offering a rich user experience out of the box, OEMs and developers often require deep customization to brand the system, integrate unique hardware features, or streamline the user interface for automotive safety and usability. This lab focuses on reverse engineering and modifying core components of the AAOS System UI: the status bar and notification panels. These elements are critical for user interaction and system feedback, and tailoring them can significantly enhance the automotive user experience.

Understanding and modifying the System UI requires a blend of Android framework knowledge, reverse engineering techniques, and practical deployment skills. We’ll dive into identifying the relevant APKs, decompiling them, making targeted changes to layout and logic, and finally, recompiling and deploying our custom System UI.

Prerequisites and Environment Setup

Before beginning, ensure you have the following:

• An AAOS build environment or access to an AAOS device with root capabilities.
• Android SDK Platform Tools (ADB).
• Java Development Kit (JDK).
• Apktool for decompiling and recompiling APKs.
• Jadx-GUI (optional, for easier code inspection).
• A custom signing key (for signing modified APKs).

Familiarity with the Android build system and basic Linux command-line operations is also highly recommended.

Understanding the SystemUI.apk

At the heart of the Android System UI lies the SystemUI.apk. This application is responsible for drawing the status bar, navigation bar (if present), notification shade, quick settings, and other system-level UI elements. Unlike regular applications, SystemUI.apk runs as a system process with elevated privileges, making its modification a powerful, yet delicate, operation.

You can locate SystemUI.apk on your AAOS device (or in your AOSP build output) typically at /system/priv-app/SystemUI/SystemUI.apk or /system_ext/priv-app/SystemUI/SystemUI.apk.

Step 1: Pulling and Decompiling SystemUI.apk

First, pull the target APK from your device:

adb rootadb pull /system/priv-app/SystemUI/SystemUI.apk .

Next, use Apktool to decompile it. This will extract its resources (layouts, assets, manifests) and convert its Dalvik bytecode into Smali assembly code, which is human-readable (though still low-level).

apktool d SystemUI.apk -o SystemUI_Decompiled

This command creates a new directory, SystemUI_Decompiled, containing the decompiled contents.

Modifying the Status Bar

The status bar in AAOS displays crucial information like network status, time, and system icons. Customizing it often involves altering XML layouts or injecting logic into the Java (Smali) code that manages these views.

Step 2: Locating and Modifying Status Bar Layouts

Navigate to the res/layout directory within your SystemUI_Decompiled folder. You’ll typically find layouts like status_bar.xml or car_status_bar.xml, which define the structure of the status bar.

Let’s say we want to remove the Ethernet icon from the status bar. This icon is usually managed by a specific `ImageView` or `ViewGroup` within the status bar layout.

1. Open SystemUI_Decompiled/res/layout/car_status_bar.xml (or relevant status bar XML).
2. Locate the XML element corresponding to the Ethernet icon. It might look something like this:

<ImageView    android:id="@id/ethernet"    android:layout_width="wrap_content"    android:layout_height="wrap_content"    android:src="@drawable/stat_sys_ethernet"    android:visibility="visible" />

To hide it, simply change its visibility attribute:

<ImageView    android:id="@id/ethernet"    android:layout_width="wrap_content"    android:layout_height="wrap_content"    android:src="@drawable/stat_sys_ethernet"    android:visibility="gone" />

Alternatively, you could comment out or remove the entire element, but changing visibility is safer for initial tests.

Modifying the Notification Panel

The notification panel (or shade) is where users interact with notifications and quick settings. Customizations here can range from visual tweaks to adding entirely new quick setting tiles.

Step 3: Customizing Notification Panel Appearance

The main layout for the notification panel is often found in res/layout/super_power_save_notification_panel.xml or similar names like car_notification_panel.xml. The core of notification stacking is handled by a component like NotificationStackScrollLayout.

Let’s adjust the padding or background of the notification stack:

1. Open SystemUI_Decompiled/res/layout/super_power_save_notification_panel.xml.
2. Find the <com.android.systemui.statusbar.phone.NotificationStackScrollLayout> or similar element.
3. Modify its attributes. For instance, to add top padding:

<com.android.systemui.statusbar.phone.NotificationStackScrollLayout    android:id="@id/notification_stack_scroller"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:paddingTop="16dp"    ... />

Step 4: Introducing Logical Changes (Smali Overview)

While layout changes are straightforward, deeper modifications might require altering Smali code. For example, to add a custom quick settings tile, you’d need to modify the Java logic that discovers and displays these tiles. This often involves looking at classes like QuickSettingsController.smali or Tile.smali in the smali_classesX directories.

Modifying Smali directly is complex. For instance, to add a simple debug log when a specific method is called:

.method public onCreate()V    .locals 0    .prologue    .line 123    invoke-super {p0}, Landroid/app/Activity;->onCreate(Landroid/os/Bundle;)V    const-string v0, "MySystemUI"    const-string v1, "onCreate called!"    invoke-static {v0, v1}, Landroid/util/Log;->d(Ljava/lang/String;Ljava/lang/String;)I    .line 125    return-void.end method

This is a simplified example. Real-world Smali modifications are far more intricate and typically involve understanding method signatures, registers, and Dalvik opcodes. For significant feature additions like a custom Quick Settings tile, it’s often more practical to integrate into the AOSP source and build rather than solely relying on Smali patching.

Recompilation, Signing, and Deployment

After making your modifications, you need to recompile the APK, sign it, and push it back to the device.

Step 5: Recompiling the APK

Use Apktool to rebuild the APK from your modified directory:

apktool b SystemUI_Decompiled -o SystemUI_Modified.apk

Step 6: Signing the Modified APK

System applications must be signed with a system key to function correctly. If you’re working with a full AOSP build, you’d typically sign with the platform key. For reverse engineering on a rooted device, you’ll need to generate your own debug key or use an existing one.

Generate a debug key (if you don’t have one):

keytool -genkey -v -keystore debug.keystore -alias debug -keyalg RSA -keysize 2048 -validity 10000

Sign your modified APK using apksigner (part of the Android SDK build tools):

/path/to/android-sdk/build-tools/VERSION/apksigner sign --ks debug.keystore --ks-key-alias debug SystemUI_Modified.apk

Replace VERSION with your installed Android build tools version (e.g., 30.0.3).

Step 7: Deploying and Testing

Push the signed APK back to the device. You’ll need to remount the /system partition as writable and replace the original APK. Ensure you back up the original SystemUI.apk first!

adb rootadb remountadb shell mv /system/priv-app/SystemUI/SystemUI.apk /system/priv-app/SystemUI/SystemUI.apk.bakadb push SystemUI_Modified.apk /system/priv-app/SystemUI/SystemUI.apkadb shell chmod 644 /system/priv-app/SystemUI/SystemUI.apk

After pushing, you must reboot the device for the changes to take effect:

adb reboot

Upon reboot, observe the status bar and notification panel. Your modifications should now be visible.

Best Practices and Caution

• Always back up original files before modifying.
• Test changes incrementally to isolate issues.
• Be aware that incorrect modifications to SystemUI.apk can soft-brick your device, requiring a factory reset or re-flashing the system image.
• For significant features, consider building from AOSP source, which offers a more robust and maintainable approach than direct APK patching.

Conclusion

Reverse engineering and modifying the AAOS System UI offers unparalleled control over the user experience. By understanding the structure of SystemUI.apk, utilizing tools like Apktool, and carefully applying changes to layout and logic, developers can create truly bespoke automotive interfaces. This lab provides a foundational understanding, empowering you to explore deeper customizations and contribute to innovative in-car experiences.