SystemUI 启动流程
启动流程主要有两个部分
- 在 framework 中启动 SystemUIService
- 在 SystemUIService 中启动 SystemUI 所需的各种组件
SystemUI 是一个系统应用，即为一个apk。所以它也会有入口 application 。它是由SystemServer 进程启动的。
注：参考 android-12.0.0_r3 分支中的代码(网站可能会出现无法打开的情况，可以参考Android官方的AndroidCodeSearch)
framework 中的流程
SystemServer
在 SystemServer.java (frameworks/base/services/java/com/android/server/SystemServer.java) 中
进程入口会启动很多和系统相关的应用、服务。
606 /**
607 * The main entry point from zygote.
608 */
609 public static void main(String[] args) {
610 new SystemServer().run();
611 }
注释中说明，SystemUI 是由 Zygote (Zygote相关参考文章)
进程启动的。
2929 t.traceBegin("StartSystemUI");
2930 try {
2931 startSystemUi(context, windowManagerF);
2932 } catch (Throwable e) {
2933 reportWtf("starting System UI", e);
2934 }
2935 t.traceEnd();
2936
2937 t.traceEnd(); // startOtherServices
其中 startSystemUi 方法实现如下。
3024 private static void startSystemUi(Context context, WindowManagerService windowManager) {
3025 PackageManagerInternal pm = LocalServices.getService(PackageManagerInternal.class);
3026 Intent intent = new Intent();
3027 intent.setComponent(pm.getSystemUiServiceComponent());
3028 intent.addFlags(Intent.FLAG_DEBUG_TRIAGED_MISSING);
3029 //Slog.d(TAG, "Starting service: " + intent);
3030 context.startServiceAsUser(intent, UserHandle.SYSTEM);
3031 windowManager.onSystemUiStarted();
3032 }
这里通过 PackageManagerInternal.getSystemUiServiceComponent() 方法获取到了 SystemUIService 组件,然后通过 startServiceAsUser 方法启动了服务。
PackageManagerInternal
372 /**
373 * @return The SystemUI service component name.
374 */
375 public abstract ComponentName getSystemUiServiceComponent();
这个方法在 PackageManagerInternal中是个抽象方法。考虑 PMS(PackageManagerService)。
里面有一个 PackageManagerInternalImpl 的内部类继承了 PackageManagerInternal 并实现了 getSystemUiServiceComponent() 方法。
27032 private class PackageManagerInternalImpl extends PackageManagerInternal {
...
27449 @Override
27450 public ComponentName getSystemUiServiceComponent() {
27451 return ComponentName.unflattenFromString(mContext
.getResources()
.getString(
27452 com.android.internal.R.string.config_systemUIServiceComponent));
27453 }
其中 config_systemUIServiceComponent 在 frameworks/base/core/res/res/values/config.xml 中
2865 <!-- SystemUi service component -->
2866 <string name="config_systemUIServiceComponent" translatable="false"
2867 >com.android.systemui/com.android.systemui.SystemUIService</string>
小结: framework中的 SystemServer 中的 run 方法启动了系统所需要的各种服务，其中就包括了 SystemUIService。
具体: 通过 PackageManagerInternal 获取到 SystemUIService 的配置名称，然后通过 startServiceAsUser 方法在 startSystemUi 中启动了服务。
SystemUI中的流程
路径 frameworks/base/packages/SystemUI/
SystemUIApplication
onCreate()方法
@Override
public void onCreate() {
super.onCreate();
Log.v(TAG, "SystemUIApplication created.");
...
...
if (Process.myUserHandle().equals(UserHandle.SYSTEM)) {
// 一般情况下走这里来，例如开关机启动系统
...
registerReceiver(new BroadcastReceiver() {
@Override
public void onReceive(Context context, Intent intent) {
if (mBootCompleteCache.isBootComplete()) return;
if (DEBUG) Log.v(TAG, "BOOT_COMPLETED received");
unregisterReceiver(this);
mBootCompleteCache.setBootComplete();
if (mServicesStarted) {
final int N = mServices.length;
for (int i = 0; i < N; i++) {
mServices[i].onBootCompleted();
}
}
}
}, bootCompletedFilter);
...
} else {
//多用户或其它非系统操作启动 SystemUi
// We don't need to startServices for sub-process that is doing some tasks.
// (screenshots, sweetsweetdesserts or tuner ..)
String processName = ActivityThread.currentProcessName();
ApplicationInfo info = getApplicationInfo();
if (processName != null && processName.startsWith(info.processName + ":")) {
return;
}
// For a secondary user, boot-completed will never be called because it has already
// been broadcasted on startup for the primary SystemUI process. Instead, for
// components which require the SystemUI component to be initialized per-user, we
// start those components now for the current non-system user.
startSecondaryUserServicesIfNeeded();
}
}
-
如果是系统启动的就会进入到这个分支中，注册监听
boot completed的通知，最后启动完全启动后就会通知各个组件onBootCompleted -
如果不是系统启动，例如多用户登录使用的情况，这时候系统其实已经启动过了，就会走
else的分支进入到startSecondaryUserServicesIfNeeded()用于启动SystemUI所需的服务组件，这个分支是根据用户来启动相应的服务的。
/**
* Ensures that all the Secondary user SystemUI services are running. If they are already
* running, this is a no-op. This is needed to conditionally start all the services, as we only
* need to have it in the main process.
* <p>This method must only be called from the main thread.</p>
*/
void startSecondaryUserServicesIfNeeded() {
String[] names = SystemUIFactory.getInstance().getSystemUIServiceComponentsPerUser(
getResources());
startServicesIfNeeded(/* metricsPrefix= */ "StartSecondaryServices", names);
}
通过SystemUIFactory获取到服务组件的名称，然后执行startServicesIfNeeded()启动服务组件。
/**
* Returns the list of system UI components that should be started per user.
*/
public String[] getSystemUIServiceComponentsPerUser(Resources resources) {
return resources.getStringArray(R.array.config_systemUIServiceComponentsPerUser);
}
组件名为config_systemUIServiceComponentsPerUser
<!-- SystemUI Services (per user): The classes of the stuff to start for each user. This is a subset of the config_systemUIServiceComponents -->
<string-array name="config_systemUIServiceComponentsPerUser" translatable="false">
<item>com.android.systemui.util.NotificationChannels</item>
</string-array>
SystemUIService
@Override
public void onCreate() {
super.onCreate();
// Start all of SystemUI
((SystemUIApplication) getApplication()).startServicesIfNeeded();
// Finish initializing dump logic
mLogBufferFreezer.attach(mBroadcastDispatcher);
...
...
// Bind the dump service so we can dump extra info during a bug report
startServiceAsUser(
new Intent(getApplicationContext(), SystemUIAuxiliaryDumpService.class),
UserHandle.SYSTEM);
}
SystemUIApplication.java中
/**
* Makes sure that all the SystemUI services are running. If they are already running,
this is a
* no-op. This is needed to conditinally start all the services,
as we only need to have it in
* the main process.
* <p>This method must only be called from the main thread.</p>
*/
public void startServicesIfNeeded() {
String[] names = SystemUIFactory.getInstance()
.getSystemUIServiceComponents(getResources());
startServicesIfNeeded(/* metricsPrefix= */ "StartServices", names);
}
getSystemUIServiceComponents与getSystemUIServiceComponentsPerUser流程一致
小结:
SystemServer启动SystemUIService之后，就进入到了应用层中，SystemUIApplication是SystemUI的入口，在onCreate方法中做了一些初始化工作，注册监听通知等操作；如果是多用户则会启动了一个组件NotificationChannels； 然后就进入到SystemUIService中，它在onCreate方法中也是执行了SystemUIApplication中的startServicesIfNeeded()方法，并把所有的服务都存在mServices数组中。
总结
SystemUI 是一个 persistent 应用，它由操作系统启动，主要流程为
Android系统在开机后会创建SystemServer进程，它会启动各种系统所需要的服务，其中就包括SystemUIService。SystemUIService启动后进入到应用层SystemUI中，在SystemUIApplication它首先会初始化监听boot completed等通知，待系统完成启动后会通知各个组件onBootCompleted。- 在进入
SystemUIService中依然执行的SystemUIApplication中的startServicesIfNeeded()方法启动所有SystemUI中的组件。 - 最终的服务启动逻辑都是在
SystemUIApplication里面，并且都保存在mServices数组中。
参考文章：
SystemUI 开发之启动流程
Zygote相关
