注意：本文基于 Android 11/R 进行分析
Qidi 2023.11.28 (MarkDown & Haroopad)
0. 简介 Android RO (Resource Overlay) 机制
Overlay 实现的效果正如其字面意思，就是“在原有效果的基础上再叠加一些效果”。
Android 提供了两种实现方式：
- 编译时：https://source.android.com/docs/setup/create/new-device#use-resource-overlays
- 运行时：https://source.android.com/docs/core/runtime/rros
通过 RO 机制，我们就可以将自己编写的 Java 服务在系统启动时运行起来。
1. 实现自定义 Java 服务
假设我们要实现的自定义服务名叫 myService，为了使它可以正常被 CarAudioService 拉起，需要在myService的 AndroidManifest.xml 中添加 directBootAware 属性：
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
coreApp="true"
tools:ignore="MissingVersion"
package="com.your_company_name.myService"
android:sharedUserId="android.uid.system">
......
<application
android:allowBackup="true"
tools:ignore="All"
android:label="myService"
android:persistent="true"
android:directBootAware="true"
android:supportsRtl="true" >
<service
android:name=".myService"
android:singleUser="true"
android:exported="true"
android:permission="android.car.permission.CAR_CONTROL_AUDIO_SETTINGS"
tools:ignore="All"
android:enabled="true">
<intent-filter>
<action android:name="com.your_company_name.myService"/>
</intent-filter>
</service>
<!-- functionalities of myService depend on calls to below libraries -->
<uses-library
android:name="com.your_company_name.audio"
android:required="true"/>
<uses-library
android:name="com.your_company_name.effect"
android:required="true"/>
</application>
</manifest>
随后实现 myService 代码，和实现普通 service 没有区别，示例 vendor/your_company_name/packages/src/com/your_company_name/myService.java 如下：
package com.your_company_name.myService;
// some dependent packages
import android.util.Log;
import xxxx;
public class myService extends Service {
private static final String TAG = "myService";
......
@Override
public IBinder onBind(Intent intent) {
// return a binder object to caller
}
@Override
public int onStartCommand(Intent intent, int flags, int startId) {
return START_STICKY;
}
@Override
public void onCreate() {
Log.i(TAG, "Creating myService...");
super.onCreate();
// creating and initializing myService
}
// implementation of some myService methods here
......
@Override
public boolean onUnbind(Intent intent) {
return super.onUnbind(intent);
}
@Override
public void onDestroy() {
super.onDestroy();
}
@Override
protected void attachBaseContext(Context base) {
super.attachBaseContext(base);
}
}
如此，自定义服务 myService 就编写完成了。接下来我们还要做一些改动，让 myService 在系统启动时能自动被 CarAudioService 拉起。
2. 对 CarAudioService 配置文件进行编译时 Overlay
为 CarAudioService 新建 Overlay 配置文件device/your_company_name/qcom/lunch_target_name/overlay/packages/services/Car/service/res/values/config.xml：
<resources>
<!-- The services that needs to be started earlier in the boot sequence and in particular order.
Every item in this array contains a flatten component name of a service that needs to be
started and a list of parameters after hashtag symbol. Here's the format:
<item>com.bar.foo/.Service#bind={bind|start|startForeground},user={all|system|foreground},
trigger={asap,userUnlocked}</item>
bind: bind - start service with Context#bindService
start - start service with Context#startService
startForeground - start service with Context#startForegroundService
If service was bound it will be restarted unless it is constantly crashing.
The default value is 'start'
user: all - the service will be bound/started for system and all foreground users
system - the service will be started/bound only for system user (u0)
foreground - the service will be bound/started only for foreground users
The default value is 'all'
trigger: indicates when the service needs to be started/bound
asap - the service might be bound when user is not fully loaded, be careful with
this value, the service also needs to have directBootAware flag set to true
userUnlocked - start service when user unlocked the device
The default value is 'userUnlocked'
If the service bound/started for foreground user it will be unbound/stopped when user
is no longer foreground.
-->
<string-array translatable="false" name="config_earlyStartupServices">
<item>com.your_company_name.myService/.myService#bind=start,user=system,trigger=asap</item>
</string-array>
</resources>
然后在 makefile 中将上述 overlay 文件路径添加到环境变量 PRODUCT_PACKAGE_OVERLAYS 中。以我使用的代码环境为例，在 device/your_company_name/qcom/lunch_target_name/lunch_target_name.mk 中添加以下语句（当然你也可以添加到别的 makefile 中，比如 device.mk）：文章来源：https://www.toymoban.com/news/detail-750642.html
PRODUCT_PACKAGE_OVERLAYS += device/your_company_name/qcom/$(TARGET_PRODUCT)/overlay
至此，所有需要的改动都已完成。接下来只要确保编译通过，并烧写到板子上，就能在开机日志中看到 myService 被拉起来的打印了。文章来源地址https://www.toymoban.com/news/detail-750642.html
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