前言
上周去深圳后海OPPO面试，面试framework相关的岗位，面试官看到我的简历里面写有关一个SystemUI的项目，问了很多相关的问题，比如SystemUI的启动流程、通知模块的流程原理等等。SystemUI的启动流程其实之前有看过源码，但是面试回答的时候没有回答的很详细，可能还是准备不足，今天这篇博客也详细记录一下SystemUI 在Android源码中的启动流程吧。本篇博客代码基于Android 8.0,其他Android 版本也适用。
一、SystemServer 启动服务
相关源码：frameworks/base/services/java/com/android/server/SystemServer.java
systemserver里面回启动很多Android的系统服务，我们看看他的启动入口main函数里面执行了run方法，这个方法很长，但是
这个方法最重要的是startBootstrapServices、startCoreServices、startOtherServices 这三个方法。
/**
* The main entry point from zygote.
*/
public static void main(String[] args) {
new SystemServer().run();
}
...
...
private void run() {
...
startBootstrapServices();
startCoreServices();
startOtherServices()
...
}
这里
startBootstrapServices() 主要用于启动系统Boot级服务，AMS也是在这里被启动的。
startCoreServices() 主要用于启动系统核心的服务，比如BatteryService、WebViewUpdateService等等。
startOtherServices() 主要用于启动一些非紧要或者是非需要及时启动的服务。
二、startOtherServices 做了哪些事情
startOtherServices启动了很多服务，比如下列的这些网络、输入、窗口等服务。
private void startOtherServices() {
final Context context = mSystemContext;
VibratorService vibrator = null;
IStorageManager storageManager = null;
NetworkManagementService networkManagement = null;
NetworkStatsService networkStats = null;
NetworkPolicyManagerService networkPolicy = null;
ConnectivityService connectivity = null;
NetworkScoreService networkScore = null;
NsdService serviceDiscovery= null;
WindowManagerService wm = null;
SerialService serial = null;
NetworkTimeUpdateService networkTimeUpdater = null;
CommonTimeManagementService commonTimeMgmtService = null;
InputManagerService inputManager = null;
TelephonyRegistry telephonyRegistry = null;
ConsumerIrService consumerIr = null;
MmsServiceBroker mmsService = null;
HardwarePropertiesManagerService hardwarePropertiesService = null;
这里面我们看到ststemUI的启动服务：
try {
startSystemUi(context, windowManagerF);
} catch (Throwable e) {
reportWtf("starting System UI", e);
}
我们看看startSystemUi 做了哪些事情,原来是通过包名、类名启动systemUI 的服务。
static final void startSystemUi(Context context, WindowManagerService windowManager) {
Intent intent = new Intent();
intent.setComponent(new ComponentName("com.android.systemui",
"com.android.systemui.SystemUIService"));
intent.addFlags(Intent.FLAG_DEBUG_TRIAGED_MISSING);
//Slog.d(TAG, "Starting service: " + intent);
context.startServiceAsUser(intent, UserHandle.SYSTEM);
windowManager.onSystemUiStarted();
}
总结一下SystemServer中启动SystemUI服务的调用流程是：SystemServer().main-->SystemServer().run()-->startOtherServices()-->startSystemUi() 接下来我们看看"com.android.systemui.SystemUIService"这个service
二、SystemUI的内部启动流程
相关源码：frameworks/base/packages/SystemUI/src/com/android/systemui/SystemUIService.java
首先我们看看SystemUIService.java,在onCreate中执行了startServicesIfNeeded
@Override
public void onCreate() {
super.onCreate();
((SystemUIApplication) getApplication()).startServicesIfNeeded();
// For debugging RescueParty
if (Build.IS_DEBUGGABLE && SystemProperties.getBoolean("debug.crash_sysui", false)) {
throw new RuntimeException();
}
源生的systemUI服务里面有这些模块
private final Class<?>[] SERVICES = new Class[] {
Dependency.class,
NotificationChannels.class,
CommandQueue.CommandQueueStart.class,
KeyguardViewMediator.class,
Recents.class,
VolumeUI.class,
Divider.class,
SystemBars.class,
StorageNotification.class,
PowerUI.class,
RingtonePlayer.class,
KeyboardUI.class,
PipUI.class,
ShortcutKeyDispatcher.class,
VendorServices.class,
GarbageMonitor.Service.class,
LatencyTester.class,
GlobalActionsComponent.class,
RoundedCorners.class,
};
startServicesIfNeeded 方法中会依次启动这些服务。
private void startServicesIfNeeded(Class<?>[] services) {
if (mServicesStarted) {
return;
}
if (!mBootCompleted) {
// check to see if maybe it was already completed long before we began
// see ActivityManagerService.finishBooting()
if ("1".equals(SystemProperties.get("sys.boot_completed"))) {
mBootCompleted = true;
if (DEBUG) Log.v(TAG, "BOOT_COMPLETED was already sent");
}
}
Log.v(TAG, "Starting SystemUI services for user " +
Process.myUserHandle().getIdentifier() + ".");
TimingsTraceLog log = new TimingsTraceLog("SystemUIBootTiming",
Trace.TRACE_TAG_APP);
log.traceBegin("StartServices");
final int N = services.length;
for (int i = 0; i < N; i++) {
Class<?> cl = services[i];
if (DEBUG) Log.d(TAG, "loading: " + cl);
log.traceBegin("StartServices" + cl.getSimpleName());
long ti = System.currentTimeMillis();
try {
Object newService = SystemUIFactory.getInstance().createInstance(cl);
mServices[i] = (SystemUI) ((newService == null) ? cl.newInstance() : newService);
} catch (IllegalAccessException ex) {
throw new RuntimeException(ex);
} catch (InstantiationException ex) {
throw new RuntimeException(ex);
}
mServices[i].mContext = this;
mServices[i].mComponents = mComponents;
if (DEBUG) Log.d(TAG, "running: " + mServices[i]);
mServices[i].start();
log.traceEnd();
// Warn if initialization of component takes too long
ti = System.currentTimeMillis() - ti;
if (ti > 1000) {
Log.w(TAG, "Initialization of " + cl.getName() + " took " + ti + " ms");
}
if (mBootCompleted) {
mServices[i].onBootCompleted();
}
}
log.traceEnd();
Dependency.get(PluginManager.class).addPluginListener(
new PluginListener<OverlayPlugin>() {
private ArraySet<OverlayPlugin> mOverlays;
@Override
public void onPluginConnected(OverlayPlugin plugin, Context pluginContext) {
StatusBar statusBar = getComponent(StatusBar.class);
if (statusBar != null) {
plugin.setup(statusBar.getStatusBarWindow(),
statusBar.getNavigationBarView());
}
// Lazy init.
if (mOverlays == null) mOverlays = new ArraySet<>();
if (plugin.holdStatusBarOpen()) {
mOverlays.add(plugin);
Dependency.get(StatusBarWindowManager.class).setStateListener(b ->
mOverlays.forEach(o -> o.setCollapseDesired(b)));
Dependency.get(StatusBarWindowManager.class).setForcePluginOpen(
mOverlays.size() != 0);
}
}
@Override
public void onPluginDisconnected(OverlayPlugin plugin) {
mOverlays.remove(plugin);
Dependency.get(StatusBarWindowManager.class).setForcePluginOpen(
mOverlays.size() != 0);
}
}, OverlayPlugin.class, true /* Allow multiple plugins */);
mServicesStarted = true;
}
到这里SystemUI 的启动就分析完了，下一篇博客分析一下Notification通知。
