本文流程基於Android 9.0
在SystemServer
中有一個方法startSystemUi
,當系統啓動後,會執行到SystemServer
的startSystemUi()
方法,正是在這個方法中啓動了SystemUIService
。
static final void startSystemUi(Context context, WindowManagerService windowManager) { Intent intent = new Intent(); // 指定了systemui的包名"com.android.systemui",指定了ServiceUIService的類名"com.android.systemui.SystemUIService" 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(); }
@Override public void onCreate() { super.onCreate(); //在oncreate方法中調用SystemUIApplication的startServicesIfNeeded來啓動相關服務 ((SystemUIApplication) getApplication()).startServicesIfNeeded(); // code... }
/** * 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 = getResources().getStringArray(R.array.config_systemUIServiceComponents); startServicesIfNeeded(names); }
注意,這裏的service
的names
是從config
文件中讀取出來的,具體內容如下,其中就包含了SystemBars
的路徑:
<!-- SystemUI Services: The classes of the stuff to start. --> <string-array name="config_systemUIServiceComponents" translatable="false"> <item>com.android.systemui.Dependency</item> <item>com.android.systemui.util.NotificationChannels</item> <item>com.android.systemui.statusbar.CommandQueue$CommandQueueStart</item> <item>com.android.systemui.keyguard.KeyguardViewMediator</item> <item>com.android.systemui.recents.Recents</item> <item>com.android.systemui.volume.VolumeUI</item> <item>com.android.systemui.stackdivider.Divider</item> <item>com.android.systemui.SystemBars</item> <item>com.android.systemui.usb.StorageNotification</item> <item>com.android.systemui.power.PowerUI</item> <item>com.android.systemui.media.RingtonePlayer</item> <item>com.android.systemui.keyboard.KeyboardUI</item> <item>com.android.systemui.pip.PipUI</item> <item>com.android.systemui.shortcut.ShortcutKeyDispatcher</item> <item>@string/config_systemUIVendorServiceComponent</item> <item>com.android.systemui.util.leak.GarbageMonitor$Service</item> <item>com.android.systemui.LatencyTester</item> <item>com.android.systemui.globalactions.GlobalActionsComponent</item> <item>com.android.systemui.ScreenDecorations</item> <item>com.android.systemui.fingerprint.FingerprintDialogImpl</item> <item>com.android.systemui.SliceBroadcastRelayHandler</item> </string-array>
具體的啓動過程
private void startServicesIfNeeded(String[] services) { //這裏就是方法名IfNeeded的原因,首先會判斷boolean變量mServicesStarted是否爲ture,爲true,表示服務已經啓動,就不需要執行後面的啓動流程了 if (mServicesStarted) { return; } //定義一個用於啓動SystemUI服務的數組,並且這些要啓動的服務都是繼承自SystemUI的 mServices = new SystemUI[services.length]; 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; //通過遍歷,將所有的服務啓動起來 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]); //調用各個服務重寫了的start()方法 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 " + cls.getName() + " took " + ti + " ms"); } if (mBootCompleted) { mServices[i].onBootCompleted(); } } // code... //啓動過一次後,就將mServicesStarted置爲true,避免重複啓動 mServicesStarted = true; }
關於SystemBars
類的註釋是這樣的,「根據產品配置,使用進程內實現,確保一個status bar
服務能夠一直運行」。
/** * Ensure a single status bar service implementation is running at all times, using the in-process * implementation according to the product config. */
那麼status bar
是怎樣啓動的呢?在SystemUIApplication
中也是通過調用SystemBars
的start()
方法,在SystemBars
中的start()
方法中去啓動statusbar
。
@Override public void start() { if (DEBUG) Log.d(TAG, "start"); createStatusBarFromConfig(); }
private void createStatusBarFromConfig() { if (DEBUG) Log.d(TAG, "createStatusBarFromConfig"); final String clsName = mContext.getString(R.string.config_statusBarComponent); if (clsName == null || clsName.length() == 0) { throw andLog("No status bar component configured", null); } Class<?> cls = null; try { cls = mContext.getClassLoader().loadClass(clsName); } catch (Throwable t) { throw andLog("Error loading status bar component: " + clsName, t); } try { mStatusBar = (SystemUI) cls.newInstance(); } catch (Throwable t) { throw andLog("Error creating status bar component: " + clsName, t); } mStatusBar.mContext = mContext; mStatusBar.mComponents = mComponents; mStatusBar.start(); if (DEBUG) Log.d(TAG, "started " + mStatusBar.getClass().getSimpleName()); }
這裏的clsName
和之前服務的names
一樣,也是從config
中讀取的,具體如下,是StatusBar
的類路徑。
<!-- Component to be used as the status bar service. Must implement the IStatusBar interface. This name is in the ComponentName flattened format (package/class) --> <string name="config_statusBarComponent" translatable="false">com.android.systemui.statusbar.phone.StatusBar</string>
於是乎,通過這樣一種方式,就啓動起來一個一直運行着的StatusBar
服務了。