最后调到ActivityStack.resumeTopActivityInnerLocked时，将要启动的应用还没起来，故走else逻辑-调用函数ActivityStackSupervisor.startSpecificActivityLocked.
14.ActivityStackSupervisor.startSpecificActivityLocked
该函数定义在frameworks/base/services/java/com/android/server/am/ActivityStackSupervisor.java文件中：
public final class ActivityStackSupervisor implements DisplayListener { ...... void startSpecificActivityLocked(ActivityRecord r, boolean andResume, boolean checkConfig) { // Is this activity's application already running? ProcessRecord app = mService.getProcessRecordLocked(r.processName, r.info.applicationInfo.uid, true); if (r.task != null && r.task.stack != null) { r.task.stack.setLaunchTime(r); } else { Slog.w(TAG, "Stack or task of activity:" + r + " is null, will not setLaunchTime for it."); } if (app != null && app.thread != null) { try { if ((r.info.flags&ActivityInfo.FLAG_MULTIPROCESS) == 0 || !"android".equals(r.info.packageName)) { // Don't add this if it is a platform component that is marked // to run in multiple processes, because this is actually // part of the framework so doesn't make sense to track as a // separate apk in the process. app.addPackage(r.info.packageName, r.info.applicationInfo.versionCode, mService.mProcessStats); } realStartActivityLocked(r, app, andResume, checkConfig); return; } catch (RemoteException e) { Slog.w(TAG, "Exception when starting activity " + r.intent.getComponent().flattenToShortString(), e); } // If a dead object exception was thrown -- fall through to // restart the application. } mService.startProcessLocked(r.processName, r.info.applicationInfo, true, 0, "activity", r.intent.getComponent(), false, false, true); } }
Launcher点击应用图标启动的进程还未创建，故app为null，如果是应用内部activity中启动另一个activity将会调用realStartActivityLocked。AMS调用startProcessLocked将会为应用创建一个新的进程并在该进程中启动activity。
15.ActivityManagerService.startProcessLocked
该函数定义在frameworks/base/services/java/com/android/server/am/ActivityManagerService.java文件中：
public class ActivityManagerService extends ActivityManagerNativeEx implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback { ...... final ProcessRecord startProcessLocked(String processName, ApplicationInfo info, boolean knownToBeDead, int intentFlags, String hostingType, ComponentName hostingName, boolean allowWhileBooting, boolean isolated, boolean keepIfLarge) { return startProcessLocked(processName, info, knownToBeDead, intentFlags, hostingType, hostingName, allowWhileBooting, isolated, 0 /* isolatedUid */, keepIfLarge, null /* ABI override */, null /* entryPoint */, null /* entryPointArgs */, null /* crashHandler */); } final ProcessRecord startProcessLocked(String processName, ApplicationInfo info, boolean knownToBeDead, int intentFlags, String hostingType, ComponentName hostingName, boolean allowWhileBooting, boolean isolated, int isolatedUid, boolean keepIfLarge, String abiOverride, String entryPoint, String[] entryPointArgs, Runnable crashHandler) { long startTime = SystemClock.elapsedRealtime(); ProcessRecord app; if (!isolated) { app = getProcessRecordLocked(processName, info.uid, keepIfLarge); checkTime(startTime, "startProcess: after getProcessRecord"); if ((intentFlags & Intent.FLAG_FROM_BACKGROUND) != 0) { // If we are in the background, then check to see if this process // is bad. If so, we will just silently fail. if (mAppErrors.isBadProcessLocked(info)) { if (DEBUG_PROCESSES) Slog.v(TAG, "Bad process: " + info.uid + "/" + info.processName); return null; } } else { // When the user is explicitly starting a process, then clear its // crash count so that we won't make it bad until they see at // least one crash dialog again, and make the process good again // if it had been bad. if (DEBUG_PROCESSES) Slog.v(TAG, "Clearing bad process: " + info.uid + "/" + info.processName); mAppErrors.resetProcessCrashTimeLocked(info); if (mAppErrors.isBadProcessLocked(info)) { EventLog.writeEvent(EventLogTags.AM_PROC_GOOD, UserHandle.getUserId(info.uid), info.uid, info.processName); mAppErrors.clearBadProcessLocked(info); if (app != null) { app.bad = false; } } } } else { // If this is an isolated process, it can't re-use an existing process. app = null; } ...... checkTime(startTime, "startProcess: stepping in to startProcess"); startProcessLocked( app, hostingType, hostingNameStr, abiOverride, entryPoint, entryPointArgs); checkTime(startTime, "startProcess: done starting proc!"); return (app.pid != 0) ? app : null; } private final void startProcessLocked(ProcessRecord app, String hostingType, String hostingNameStr, String abiOverride, String entryPoint, String[] entryPointArgs) { long startTime = SystemClock.elapsedRealtime(); if (app.pid > 0 && app.pid != MY_PID) { checkTime(startTime, "startProcess: removing from pids map"); synchronized (mPidsSelfLocked) { mPidsSelfLocked.remove(app.pid); mHandler.removeMessages(PROC_START_TIMEOUT_MSG, app); } checkTime(startTime, "startProcess: done removing from pids map"); app.setPid(0); } ...... try { ...... // Start the process. It will either succeed and return a result containing // the PID of the new process, or else throw a RuntimeException. boolean isActivityProcess = (entryPoint == null); if (entryPoint == null) entryPoint = "android.app.ActivityThread"; Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "Start proc: " + app.processName); checkTime(startTime, "startProcess: asking zygote to start proc"); Process.ProcessStartResult startResult = Process.start(entryPoint, app.processName, uid, uid, gids, debugFlags, mountExternal, app.info.targetSdkVersion, app.info.seinfo, requiredAbi, instructionSet, app.info.dataDir, entryPointArgs); ...... } } ...... }
这里主要是调用Process.start接口来创建一个新的进程，新的进程会导入android.app.ActivityThread类，并且执行它的main函数，每一个应用程序都有一个ActivityThread实例来对应。
16.ActivityThread.main
该函数定义在frameworks/base/core/java/android/app/ActivityThread.java文件中：
public final class ActivityThread { ...... private final void attach(boolean system) { ...... mSystemThread = system; if (!system) { ...... IActivityManager mgr = ActivityManagerNative.getDefault(); try { mgr.attachApplication(mAppThread); } catch (RemoteException ex) { ...... } } else { ...... } } ...... public static void main(String[] args) { ...... Looper.prepareMainLooper(); ActivityThread thread = new ActivityThread(); thread.attach(false); ...... Looper.loop(); throw new RuntimeException("Main thread loop unexpectedly exited"); } }
这个函数在进程中创建一个ActivityThread实例，然后调用它的attach函数，接着就进入消息循环了，直到最后进程退出。
函数attach最终调用了ActivityManagerService的远程接口ActivityManagerProxy的attachApplication函数，传入的参数是mAppThread，这是一个ApplicationThread类型的Binder对象，它的作用是用来进行进程间通信的。
17.ActivityManagerProxy.attachApplication
该函数定义在frameworks/base/core/java/android/app/ActivityManagerNative.java文件中：
class ActivityManagerProxy implements IActivityManager { ...... public void attachApplication(IApplicationThread app) throws RemoteException { Parcel data = Parcel.obtain(); Parcel reply = Parcel.obtain(); data.writeInterfaceToken(IActivityManager.descriptor); data.writeStrongBinder(app.asBinder()); mRemote.transact(ATTACH_APPLICATION_TRANSACTION, data, reply, 0); reply.readException(); data.recycle(); reply.recycle(); } ...... }
这里通过Binder驱动程序，最后进入ActivityManagerService的attachApplication函数中。
18.ActivityManagerService.attachApplication
该函数定义在frameworks/base/services/java/com/android/server/am/ActivityManagerService.java文件中：
public final class ActivityManagerService extends ActivityManagerNative implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback { ...... @Override public void attachApplication(IApplicationThread thread) { synchronized (this) { int callingPid = Binder.getCallingPid(); final long origId = Binder.clearCallingIdentity(); attachApplicationLocked(thread, callingPid); Binder.restoreCallingIdentity(origId); } } private final boolean attachApplicationLocked(IApplicationThread thread, int pid) { ...... boolean normalMode = mProcessesReady || isAllowedWhileBooting(app.info); ...... if (normalMode) { try { if (mStackSupervisor.attachApplicationLocked(app)) { didSomething = true; } } catch (Exception e) { ...... } } } ...... }
attachApplicationLocked接着调用ActivityStackSupervisor.attachApplicationLocked接口。
19.ActivityStackSupervisor.attachApplicationLocked
该函数定义在frameworks/base/services/java/com/android/server/am/ActivityStackSupervisor.java文件中：
public final class ActivityStackSupervisor implements DisplayListener { boolean attachApplicationLocked(ProcessRecord app) throws RemoteException { final String processName = app.processName; boolean didSomething = false; for (int displayNdx = mActivityDisplays.size() - 1; displayNdx >= 0; --displayNdx) { ArrayList<ActivityStack> stacks = mActivityDisplays.valueAt(displayNdx).mStacks; for (int stackNdx = stacks.size() - 1; stackNdx >= 0; --stackNdx) { ...... if (hr != null) { if (hr.app == null && app.uid == hr.info.applicationInfo.uid && processName.equals(hr.processName)) { try { if (realStartActivityLocked(hr, app, true, true)) { didSomething = true; } } catch (RemoteException e) { ...... } } } } } if (!didSomething) { ensureActivitiesVisibleLocked(null, 0, !PRESERVE_WINDOWS); } return didSomething; } final boolean realStartActivityLocked(ActivityRecord r, ProcessRecord app, boolean andResume, boolean checkConfig) throws RemoteException { ...... try { ...... if (andResume) { app.hasShownUi = true; app.pendingUiClean = true; } app.forceProcessStateUpTo(mService.mTopProcessState); app.thread.scheduleLaunchActivity(new Intent(r.intent), r.appToken, System.identityHashCode(r), r.info, new Configuration(mService.mConfiguration), new Configuration(task.mOverrideConfig), r.compat, r.launchedFromPackage, task.voiceInteractor, app.repProcState, r.icicle, r.persistentState, results, newIntents, !andResume, mService.isNextTransitionForward(), profilerInfo); ...... } catch (RemoteException e) { ...... } } }
这里最终通过app.thread进入到ApplicationThreadProxy的scheduleLaunchActivity函数中，注意，这里的第二个参数r，是一个ActivityRecord类型的Binder对象，用来作来这个Activity的token值。
20.ApplicationThreadProxy.scheduleLaunchActivity
该函数定义在frameworks/base/core/java/android/app/ApplicationThreadNative.java文件中：
class ApplicationThreadProxy implements IApplicationThread { ...... public final void scheduleLaunchActivity(Intent intent, IBinder token, int ident, ActivityInfo info, Configuration curConfig, Configuration overrideConfig, CompatibilityInfo compatInfo, String referrer, IVoiceInteractor voiceInteractor, int procState, Bundle state, PersistableBundle persistentState, List<ResultInfo> pendingResults, List<ReferrerIntent> pendingNewIntents, boolean notResumed, boolean isForward, ProfilerInfo profilerInfo) throws RemoteException { Parcel data = Parcel.obtain(); data.writeInterfaceToken(IApplicationThread.descriptor); intent.writeToParcel(data, 0); data.writeStrongBinder(token); data.writeInt(ident); info.writeToParcel(data, 0); curConfig.writeToParcel(data, 0); if (overrideConfig != null) { data.writeInt(1); overrideConfig.writeToParcel(data, 0); } else { data.writeInt(0); } compatInfo.writeToParcel(data, 0); data.writeString(referrer); data.writeStrongBinder(voiceInteractor != null ? voiceInteractor.asBinder() : null); data.writeInt(procState); data.writeBundle(state); data.writePersistableBundle(persistentState); data.writeTypedList(pendingResults); data.writeTypedList(pendingNewIntents); data.writeInt(notResumed ? 1 : 0); data.writeInt(isForward ? 1 : 0); if (profilerInfo != null) { data.writeInt(1); profilerInfo.writeToParcel(data, Parcelable.PARCELABLE_WRITE_RETURN_VALUE); } else { data.writeInt(0); } mRemote.transact(SCHEDULE_LAUNCH_ACTIVITY_TRANSACTION, data, null, IBinder.FLAG_ONEWAY); data.recycle(); } ...... }
还是通过Binder驱动程序进入ApplicationThread的scheduleLaunchActivity函数中。
21.ApplicationThread.scheduleLaunchActivity
函数定义在frameworks/base/core/java/android/app/ActivityThread.java文件中：
public final class ActivityThread { ...... private final class ApplicationThread extends ApplicationThreadNative { @Override public final void scheduleLaunchActivity(Intent intent, IBinder token, int ident, ActivityInfo info, Configuration curConfig, Configuration overrideConfig, CompatibilityInfo compatInfo, String referrer, IVoiceInteractor voiceInteractor, int procState, Bundle state, PersistableBundle persistentState, List<ResultInfo> pendingResults, List<ReferrerIntent> pendingNewIntents, boolean notResumed, boolean isForward, ProfilerInfo profilerInfo) { updateProcessState(procState, false); ActivityClientRecord r = new ActivityClientRecord(); r.token = token; r.ident = ident; r.intent = intent; r.referrer = referrer; r.voiceInteractor = voiceInteractor; r.activityInfo = info; r.compatInfo = compatInfo; r.state = state; r.persistentState = persistentState; r.pendingResults = pendingResults; r.pendingIntents = pendingNewIntents; r.startsNotResumed = notResumed; r.isForward = isForward; r.profilerInfo = profilerInfo; r.overrideConfig = overrideConfig; updatePendingConfiguration(curConfig); sendMessage(H.LAUNCH_ACTIVITY, r); } } private void sendMessage(int what, Object obj, int arg1) { sendMessage(what, obj, arg1, 0, false); } private void sendMessage(int what, Object obj, int arg1, int arg2, boolean async) { if (DEBUG_MESSAGES) Slog.v( TAG, "SCHEDULE " + what + " " + mH.codeToString(what) + ": " + arg1 + " / " + obj); Message msg = Message.obtain(); msg.what = what; msg.obj = obj; msg.arg1 = arg1; msg.arg2 = arg2; if (async) { msg.setAsynchronous(true); } mH.sendMessage(msg); } private final class H extends Handler { ...... public void handleMessage(Message msg) { ...... 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, "LAUNCH_ACTIVITY"); Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER); } break; ...... } ...... } private void handleLaunchActivity(ActivityClientRecord r, Intent customIntent, String reason) { ...... Activity a = performLaunchActivity(r, customIntent); if (a != null) { r.createdConfig = new Configuration(mConfiguration); reportSizeConfigurations(r); Bundle oldState = r.state; handleResumeActivity(r.token, false, r.isForward, !r.activity.mFinished && !r.startsNotResumed, r.lastProcessedSeq, reason); ...... } else { ...... } } private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) { // System.out.println("##### [" + System.currentTimeMillis() + "] ActivityThread.performLaunchActivity(" + r + ")"); ActivityInfo aInfo = r.activityInfo; if (r.packageInfo == null) { r.packageInfo = getPackageInfo(aInfo.applicationInfo, r.compatInfo, Context.CONTEXT_INCLUDE_CODE); } ComponentName component = r.intent.getComponent(); if (component == null) { component = r.intent.resolveActivity( mInitialApplication.getPackageManager()); r.intent.setComponent(component); } if (r.activityInfo.targetActivity != null) { component = new ComponentName(r.activityInfo.packageName, r.activityInfo.targetActivity); } 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) { if (!mInstrumentation.onException(activity, e)) { throw new RuntimeException( "Unable to instantiate activity " + component + ": " + e.toString(), 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 (r.overrideConfig != null) { config.updateFrom(r.overrideConfig); } if (DEBUG_CONFIGURATION) Slog.v(TAG, "Launching activity " + r.activityInfo.name + " with config " + config); Window window = null; if (r.mPendingRemoveWindow != null && r.mPreserveWindow) { window = r.mPendingRemoveWindow; r.mPendingRemoveWindow = null; r.mPendingRemoveWindowManager = null; } 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, window); 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; 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; if (!r.activity.mFinished) { activity.performStart(); r.stopped = false; } if (!r.activity.mFinished) { if (r.isPersistable()) { if (r.state != null || r.persistentState != null) { mInstrumentation.callActivityOnRestoreInstanceState(activity, r.state, r.persistentState); } } else if (r.state != null) { mInstrumentation.callActivityOnRestoreInstanceState(activity, r.state); } } if (!r.activity.mFinished) { activity.mCalled = false; if (r.isPersistable()) { mInstrumentation.callActivityOnPostCreate(activity, r.state, r.persistentState); } else { mInstrumentation.callActivityOnPostCreate(activity, r.state); } if (!activity.mCalled) { throw new SuperNotCalledException( "Activity " + r.intent.getComponent().toShortString() + " did not call through to super.onPostCreate()"); } } } r.paused = true; mActivities.put(r.token, r); } catch (SuperNotCalledException e) { throw e; } catch (Exception e) { if (!mInstrumentation.onException(activity, e)) { throw new RuntimeException( "Unable to start activity " + component + ": " + e.toString(), e); } } return activity; } }
先调用performLaunchActivity函数来加载Activity，然后调用它的onCreate函数，最后回到handleLaunchActivity函数时，再调用handleResumeActivity函数来使这个Activity进入Resumed状态，即会调用这个Activity的onResume函数，这是遵循Activity的生命周期的。其中performLaunchActivity中是通过函数Instrumentation.callActivityOnCreate来间接调用Activity的onCreate函数的，
Application app = r.packageInfo.makeApplication(false, mInstrumentation);
这句是创建Application;
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, window);
这里将Application和activity关联起来，因此一个应用都有一个Application。
