Activity管理的核心是AcitivityManagerService，是一个独立的进程；
ActiveThread是每一个应用程序所在进程的主线程，循环的消息处理；
ActiveThread与AcitivityManagerService的通信是属于进程间通信，使用binder机制；
以启动一个应用程序startActivity为例看一下代码执行的大概流程：
可将其分为6个过程：
1 使用代理模式启动到ActivityManagerService中执行；
2 创建ActivityRecord到mHistory记录中；
3 通过socket通信到Zgote相关类创建process；
4 通过ApplicatonThread与ActivityManagerService建立通信；
5 ActivityManagerService通知ActiveThread启动Activity的创建；
6 ActivityThread创建Activity加入到mActivities中并开始调度Activity执行；
请看下图：
public final class ActivityThread { final ApplicationThread mAppThread = new ApplicationThread(); final Looper mLooper = Looper.myLooper(); final H mH = new H(); //在mActivities中，记录了应用程序创建的所有activity实例记录，对应的是ActivityRecord。 final ArrayMap<IBinder, ActivityClientRecord> mActivities = new ArrayMap<>(); // List of new activities (via ActivityRecord.nextIdle) that should // be reported when next we idle. ActivityClientRecord mNewActivities = null; // Number of activities that are currently visible on-screen. int mNumVisibleActivities = 0; WeakReference<AssistStructure> mLastAssistStructure; final ArrayMap<IBinder, Service> mServices = new ArrayMap<>(); Application mInitialApplication; final ArrayList<Application> mAllApplications = new ArrayList<Application>(); // set of instantiated backup agents, keyed by package name final ArrayMap<String, BackupAgent> mBackupAgents = new ArrayMap<String, BackupAgent>(); /** Reference to singleton {@link ActivityThread} */ private static ActivityThread sCurrentActivityThread; Instrumentation mInstrumentation; final ArrayMap<String, WeakReference<LoadedApk>> mPackages = new ArrayMap<String, WeakReference<LoadedApk>>(); final ArrayMap<String, WeakReference<LoadedApk>> mResourcePackages = new ArrayMap<String, WeakReference<LoadedApk>>(); final ArrayList<ActivityClientRecord> mRelaunchingActivities = new ArrayList<ActivityClientRecord>(); private final ResourcesManager mResourcesManager; // The lock of mProviderMap protects the following variables. final ArrayMap<ProviderKey, ProviderClientRecord> mProviderMap = new ArrayMap<ProviderKey, ProviderClientRecord>(); final ArrayMap<IBinder, ProviderRefCount> mProviderRefCountMap = new ArrayMap<IBinder, ProviderRefCount>(); final ArrayMap<IBinder, ProviderClientRecord> mLocalProviders = new ArrayMap<IBinder, ProviderClientRecord>(); final ArrayMap<ComponentName, ProviderClientRecord> mLocalProvidersByName = new ArrayMap<ComponentName, ProviderClientRecord>(); private class H extends Handler { public static final int LAUNCH_ACTIVITY = 100; public static final int PAUSE_ACTIVITY = 101; public static final int PAUSE_ACTIVITY_FINISHING= 102; public static final int STOP_ACTIVITY_SHOW = 103; public static final int STOP_ACTIVITY_HIDE = 104; public static final int SHOW_WINDOW = 105; public static final int HIDE_WINDOW = 106; public static final int RESUME_ACTIVITY = 107; public static final int SEND_RESULT = 108; public static final int DESTROY_ACTIVITY = 109; public static final int BIND_APPLICATION = 110; public static final int EXIT_APPLICATION = 111; public static final int NEW_INTENT = 112; public static final int RECEIVER = 113; public static final int CREATE_SERVICE = 114; public static final int SERVICE_ARGS = 115; public static final int STOP_SERVICE = 116; public static final int CONFIGURATION_CHANGED = 118; public static final int CLEAN_UP_CONTEXT = 119; public static final int GC_WHEN_IDLE = 120; public static final int BIND_SERVICE = 121; public static final int UNBIND_SERVICE = 122; public static final int DUMP_SERVICE = 123; public static final int LOW_MEMORY = 124; public static final int ACTIVITY_CONFIGURATION_CHANGED = 125; public static final int RELAUNCH_ACTIVITY = 126; public static final int PROFILER_CONTROL = 127; public static final int CREATE_BACKUP_AGENT = 128; public static final int DESTROY_BACKUP_AGENT = 129; public static final int SUICIDE = 130; public static final int REMOVE_PROVIDER = 131; public static final int ENABLE_JIT = 132; public static final int DISPATCH_PACKAGE_BROADCAST = 133; public static final int SCHEDULE_CRASH = 134; public static final int DUMP_HEAP = 135; public static final int DUMP_ACTIVITY = 136; public static final int SLEEPING = 137; public static final int SET_CORE_SETTINGS = 138; public static final int UPDATE_PACKAGE_COMPATIBILITY_INFO = 139; public static final int TRIM_MEMORY = 140; public static final int DUMP_PROVIDER = 141; public static final int UNSTABLE_PROVIDER_DIED = 142; public static final int REQUEST_ASSIST_CONTEXT_EXTRAS = 143; public static final int TRANSLUCENT_CONVERSION_COMPLETE = 144; public static final int INSTALL_PROVIDER = 145; public static final int ON_NEW_ACTIVITY_OPTIONS = 146; public static final int CANCEL_VISIBLE_BEHIND = 147; public static final int BACKGROUND_VISIBLE_BEHIND_CHANGED = 148; public static final int ENTER_ANIMATION_COMPLETE = 149; public void handleMessage(Message msg) { if (DEBUG_MESSAGES) Slog.v(TAG, ">>> handling: " + codeToString(msg.what)); switch (msg.what) { case LAUNCH_ACTIVITY: { Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityStart"); final ActivityClientRecord r = (ActivityClientRecord) msg.obj; r.packageInfo = getPackageInfoNoCheck( r.activityInfo.applicationInfo, r.compatInfo); handleLaunchActivity(r, null); Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER); } break; case RELAUNCH_ACTIVITY: { Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityRestart"); ActivityClientRecord r = (ActivityClientRecord)msg.obj; handleRelaunchActivity(r); Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER); } break; case PAUSE_ACTIVITY: Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityPause"); handlePauseActivity((IBinder)msg.obj, false, (msg.arg1&1) != 0, msg.arg2, (msg.arg1&2) != 0); maybeSnapshot(); Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER); break; case PAUSE_ACTIVITY_FINISHING: Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityPause"); handlePauseActivity((IBinder)msg.obj, true, (msg.arg1&1) != 0, msg.arg2, (msg.arg1&1) != 0); Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER); break; case STOP_ACTIVITY_SHOW: Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityStop"); handleStopActivity((IBinder)msg.obj, true, msg.arg2); Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER); break; case STOP_ACTIVITY_HIDE: Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityStop"); handleStopActivity((IBinder)msg.obj, false, msg.arg2); Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER); break; case SHOW_WINDOW: Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityShowWindow"); handleWindowVisibility((IBinder)msg.obj, true); Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER); break; case HIDE_WINDOW: Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityHideWindow"); handleWindowVisibility((IBinder)msg.obj, false); Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER); break; case RESUME_ACTIVITY: Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityResume"); handleResumeActivity((IBinder) msg.obj, true, msg.arg1 != 0, true); Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER); break; case SEND_RESULT: Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityDeliverResult"); handleSendResult((ResultData)msg.obj); Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER); break; case DESTROY_ACTIVITY: Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityDestroy"); handleDestroyActivity((IBinder)msg.obj, msg.arg1 != 0, msg.arg2, false); Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER); break; ....................... } if (DEBUG_MESSAGES) Slog.v(TAG, "<<< done: " + codeToString(msg.what)); } } public static void main(String[] args) { //Traceview相关的统计工具 Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "ActivityThreadMain"); //启动性能分析统计 SamplingProfilerIntegration.start(); Environment.initForCurrentUser(); // Set the reporter for event logging in libcore EventLogger.setReporter(new EventLoggingReporter()); AndroidKeyStoreProvider.install(); // Make sure TrustedCertificateStore looks in the right place for CA certificates final File configDir = Environment.getUserConfigDirectory(UserHandle.myUserId()); TrustedCertificateStore.setDefaultUserDirectory(configDir); Process.setArgV0("<pre-initialized>"); Looper.prepareMainLooper(); long prioritySetTime = 0; if (args != null && args.length > 0 && "htc-activity".equals(args[0])) { Process.setThreadPriority(Process.THREAD_PRIORITY_DISPLAY); prioritySetTime = SystemClock.uptimeMillis(); } //在建立消息循环之前，会通过thread.attach(false)来初始化应用程序的运行环境， //并建立activityThread和ActivityManagerService之间的桥mAppThread， mAppThread是IApplicationThread的一个实例。 ActivityThread thread = new ActivityThread(); thread.attach(false); //每个应用程序对应着一个ActivityThread实例，应用程序由ActivityThread.main打开消息循环。 //每个应用程序同时也对应着一个ApplicationThread对象。该对象是activityThread和ActivityManagerService之间的桥梁。 if (prioritySetTime > 0) { final long start = prioritySetTime; thread.mH.postDelayed(new Runnable() { @Override public void run() { Process.setThreadPriority(Process.THREAD_PRIORITY_DEFAULT); if (DEBUG_AM) { Slog.d(TAG, "Restore main prio dur " + (SystemClock.uptimeMillis() - start)); } } }, 2000); } if (sMainThreadHandler == null) { sMainThreadHandler = thread.getHandler(); } if (false) { Looper.myLooper().setMessageLogging(new LogPrinter(Log.DEBUG, "ActivityThread")); } // End of event ActivityThreadMain. Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER); Looper.loop(); throw new RuntimeException("Main thread loop unexpectedly exited"); } private void handleLaunchActivity(ActivityClientRecord r, Intent customIntent) { Activity a = performLaunchActivity(r, customIntent); } private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) { Activity activity = null; try { java.lang.ClassLoader cl = r.packageInfo.getClassLoader(); activity = mInstrumentation.newActivity( cl, component.getClassName(), r.intent); StrictMode.incrementExpectedActivityCount(activity.getClass()); r.intent.setExtrasClassLoader(cl); r.intent.prepareToEnterProcess(); if (r.state != null) { r.state.setClassLoader(cl); } } catch (Exception e) { .... } try { Application app = r.packageInfo.makeApplication(false, mInstrumentation); if (localLOGV) Slog.v(TAG, "Performing launch of " + r); if (localLOGV) Slog.v( TAG, r + ": app=" + app + ", appName=" + app.getPackageName() + ", pkg=" + r.packageInfo.getPackageName() + ", comp=" + r.intent.getComponent().toShortString() + ", dir=" + r.packageInfo.getAppDir()); if (activity != null) { Context appContext = createBaseContextForActivity(r, activity); CharSequence title = r.activityInfo.loadLabel(appContext.getPackageManager()); Configuration config = new Configuration(mCompatConfiguration); if (DEBUG_CONFIGURATION) Slog.v(TAG, "Launching activity " + r.activityInfo.name + " with config " + config); activity.attach(appContext, this, getInstrumentation(), r.token, r.ident, app, r.intent, r.activityInfo, title, r.parent, r.embeddedID, r.lastNonConfigurationInstances, config, r.referrer, r.voiceInteractor); if (customIntent != null) { activity.mIntent = customIntent; } r.lastNonConfigurationInstances = null; activity.mStartedActivity = false; int theme = r.activityInfo.getThemeResource(); if (theme != 0) { activity.setTheme(theme); } activity.mCalled = false; //callActivityOnCreate() 调用App的onCreate()函数 if (r.isPersistable()) { mInstrumentation.callActivityOnCreate(activity, r.state, r.persistentState); } else { mInstrumentation.callActivityOnCreate(activity, r.state); } if (!activity.mCalled) { throw new SuperNotCalledException( "Activity " + r.intent.getComponent().toShortString() + " did not call through to super.onCreate()"); } r.activity = activity; r.stopped = true; .... } .... } catch (Exceptiont e) { .... } }
1.在客户端和服务端分别有一个管理activity的地方，服务端是在mHistory中，处于mHistory栈顶的就是当前处于running状态的activity，客户端是在mActivities中。
2.在startActivity时，首先会在ActivityManagerService中建立HistoryRecord，并加入到mHistory中，然后通过scheduleLaunchActivity在客户端创建ActivityRecord记录并加入到mActivities中。最终在ActivityThread发起请求，进入消息循环，完成activity的启动和窗口的管理等
