一、SystemUI组成
SystemUI是Android的系统界面，包括状态栏statusbar、锁屏keyboard、任务列表recents等等，都继承于SystemUI这个类，如锁屏KeyguardViewMediator。
二、SystemUI启动流程
SystemUI的启动由SystemServer开始。SystemServer由Zygote fork生成的，进程名为system_server，该进程承载着framework的核心服务。Zygote启动过程中会调用startSystemServer()。SystemUI的分析从SystemServer的main方法开始。SystemUI启动的大致流程如下：
2.1 SystemServer
SystemServer在run方法中负责启动系统的各种服务。
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..........
// Start services.
try {
traceBeginAndSlog("StartServices");
startBootstrapServices();
startCoreServices();
startOtherServices();
SystemServerInitThreadPool.shutdown();
} catch (Throwable ex) {
Slog.e("System", "******************************************");
Slog.e("System", "************ Failure starting system services", ex);
throw ex;
} finally {
traceEnd();
}
在startOtherServices方法中先是创建并添加WindowManagerService、InputManagerService等service,并且调用startSystemUi方法，跳转SystemUIService。
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private void startOtherServices() {
//创建，注册服务
...
WindowManagerService wm = null;
SerialService serial = null;
NetworkTimeUpdateService networkTimeUpdater = null;
CommonTimeManagementService commonTimeMgmtService = null;
InputManagerService inputManager = null;
...
traceBeginAndSlog("IpConnectivityMetrics");
mSystemServiceManager.startService(IpConnectivityMetrics.class);
traceEnd();
traceBeginAndSlog("NetworkWatchlistService");
mSystemServiceManager.startService(NetworkWatchlistService.Lifecycle.class);
traceEnd();
...
traceBeginAndSlog("StartSystemUI");
try {
startSystemUi(context, windowManagerF);
} catch (Throwable e) {
reportWtf("starting System UI", e);
}
启动跳转SystemUIService。
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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();
}
2.2 SystemUIService
SystemUIService在onCreate中调用SystemUIApplication的startServicesIfNeeded方法。
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@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();
}
...
}
2.3 SystemUIApplication
SystemUIApplication先获取配置的systemUI组件。
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public void startServicesIfNeeded() {
String[] names = getResources().getStringArray(R.array.config_systemUIServiceComponents);
startServicesIfNeeded(names);
}
配置文件在/frameworks/base/packages/SystemUI/res/values/config.xml中，配置的systemui组件如图：
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<string-array name="config_systemUIServiceComponents" translatable="false">
332 <item>com.android.systemui.Dependency</item>
333 <item>com.android.systemui.util.NotificationChannels</item>
334 <item>com.android.systemui.statusbar.CommandQueue$CommandQueueStart</item>
335 <item>com.android.systemui.keyguard.KeyguardViewMediator</item>
336 <item>com.android.systemui.recents.Recents</item>
337 <item>com.android.systemui.volume.VolumeUI</item>
338 <item>com.android.systemui.stackdivider.Divider</item>
339 <item>com.android.systemui.SystemBars</item>
340 <item>com.android.systemui.usb.StorageNotification</item>
341 <item>com.android.systemui.power.PowerUI</item>
342 <item>com.android.systemui.media.RingtonePlayer</item>
343 <item>com.android.systemui.keyboard.KeyboardUI</item>
344 <item>com.android.systemui.pip.PipUI</item>
345 <item>com.android.systemui.shortcut.ShortcutKeyDispatcher</item>
346 <item>@string/config_systemUIVendorServiceComponent</item>
347 <item>com.android.systemui.util.leak.GarbageMonitor$Service</item>
348 <item>com.android.systemui.LatencyTester</item>
349 <item>com.android.systemui.globalactions.GlobalActionsComponent</item>
350 <item>com.android.systemui.ScreenDecorations</item>
351 <item>com.android.systemui.fingerprint.FingerprintDialogImpl</item>
352 <item>com.android.systemui.SliceBroadcastRelayHandler</item>
353 </string-array>
在startServicesIfNeeded方法中，根据config配置创建SystemUI，并调用SystemUI的start方法。
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private void startServicesIfNeeded(String[] services) {
if (mServicesStarted) {
return;
}
mServices = new SystemUI[services.length];
final int N = services.length;
for (int i = 0; i < N; i++) {
String clsName = services[i];
if (DEBUG) Log.d(TAG, "loading: " + clsName);
log.traceBegin("StartServices" + clsName);
long ti = System.currentTimeMillis();
Class cls;
try {
cls = Class.forName(clsName);
mServices[i] = (SystemUI) cls.newInstance();
} catch(ClassNotFoundException ex){
throw new RuntimeException(ex);
} 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();
...
}
2.4 SystemUI
SystemUI是一个抽象类，start()是抽象方法，具体实现在子类。
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public abstract class SystemUI implements SysUiServiceProvider {
public Context mContext;
public Map<Class<?>, Object> mComponents;
public abstract void start();
protected void onConfigurationChanged(Configuration newConfig) {
}
public void dump(FileDescriptor fd, PrintWriter pw, String[] args) {
}
protected void onBootCompleted() {
}
...
}