Activity源码分析-白红宇

1.应用如何启动的，参考zygote启动的分析

SystemServer.run ->

mActivityManagerService.systemReady ->

startHomeActivityLocked(mCurrentUserId, "systemReady"); ->

mStackSupervisor.startHomeActivity()

2.Activity内部启动一个Activity

Activity继承子ContextThemeWrapper继承自ContextWrapper继承自Context

Actvity是在ActivityThread中被创建的：

反射构造Activity                    执行attach方法                    调用声明周期函数复制代码

所有的Activity启动，都最终调用到了startActivityForResult。这里的mParent主要是干嘛用的呢如果mParent为null，那么就直接调用mInstrumentation.execStartActivity; 如果mParent不为空，那么调用mParent.startActivityFromChild，而最终也是调用到了mInstrumentation.execStartActivity。

3734    public void startActivityForResult(Intent intent, int requestCode, @Nullable Bundle options) {3735        if (mParent == null) {3736            Instrumentation.ActivityResult ar =3737                mInstrumentation.execStartActivity(3738                    this,3738                    mMainThread.getApplicationThread()3738                    mToken, 3738                    this,3739                    intent, 3738                    requestCode, 3738                    options);3740            if (ar != null) {3741                mMainThread.sendActivityResult(3742                    mToken, mEmbeddedID, requestCode, ar.getResultCode(),3743                    ar.getResultData());3744            }3761        } else {3762           mParent.startActivityFromChild(this, intent, requestCode, options);3769        }3773    }复制代码

4284    public void startActivityFromChild(@NonNull Activity child, Intent intent,4285            int requestCode, @Nullable Bundle options) {4286        Instrumentation.ActivityResult ar =4287            mInstrumentation.execStartActivity(4288                this, mMainThread.getApplicationThread(), mToken, child,4289                intent, requestCode, options);4290        if (ar != null) {4291            mMainThread.sendActivityResult(4292                mToken, child.mEmbeddedID, requestCode,4293                ar.getResultCode(), ar.getResultData());4294        }4295    }复制代码

调用完之后，使用了ActivityThread.sendActivityResult，从mActivities中获取ActivityClientRecord，首先更新了一下可见性，但是干嘛用呢？接着调用了mInstrumentation来执行activity的onPause什么周期；最后分发了result调用了activity的onActivityResult。如果Activity已经pause了，那么不会onReusme，如果没有pause，那么会调用Activity的onResume。代码看一下：

3548    private void handleSendResult(ResultData res) {3549        ActivityClientRecord r = mActivities.get(res.token);3551        if (r != null) {3552            final boolean resumed = !r.paused;3553            if (!r.activity.mFinished && r.activity.mDecor != null3554                    && r.hideForNow && resumed) {3558                updateVisibility(r, true);3559            }3560            if (resumed) {3561                try {3563                    r.activity.mCalled = false;3564                    r.activity.mTemporaryPause = true;3565                    mInstrumentation.callActivityOnPause(r.activity);3566                    if (!r.activity.mCalled) {3570                    }3571                } catch (SuperNotCalledException e) {3580                }3581            }3582            deliverResults(r, res.results);3587        }3588    }复制代码

回到关键函数mInstrumentation.execStartActivity上来，先从mActivityMonitors中找到目标ActivityMonitor, 干嘛用的呢，通过注释看大概是已创建的Activity的缓存列表吧，看不太明白先放放；其次调用ActivityManagerNative.getDefault().startActivity();

几个参数分析一下：

who：启动其他Activity的当前Activity

contextThread：ActivityThread中的mApplicationThread

token：ActivityManagerService中ActivityRecord中传入的域IApplicationToken.Stub appToken

target：启动其他Activity的当前Activity

Intent：要启动的目标intent

requestCode：启动请求码

options：启动额外参数

1458    public ActivityResult execStartActivity(1459            Context who, IBinder contextThread, IBinder token, Activity target,1460            Intent intent, int requestCode, Bundle options) {1461        IApplicationThread whoThread = (IApplicationThread) contextThread;1462        if (mActivityMonitors != null) {1463            synchronized (mSync) {1464                final int N = mActivityMonitors.size();1465                for (int i=0; i
    
     = 0 ? am.getResult() : null;1471                        }1472                        break;1473                    }1474                }1475            }1476        }1477        try {1478            intent.migrateExtraStreamToClipData();1479            intent.prepareToLeaveProcess();1480            int result = 1481                ActivityManagerNative.getDefault().startActivity(1481                       whoThread, 1481                       who.getBasePackageName(), 1481                       intent,1482                       intent.resolveTypeIfNeeded(who.getContentResolver()),1483                       token, 1481                       target != null ? target.mEmbeddedID : null,1484                       requestCode, 1481                       0, 1481                       null, 1481                       options);1485            checkStartActivityResult(result, intent);1486        } catch (RemoteException e) {1487        }1488        return null;1489    }复制代码

看看关键函数吧ActivityManagerNative.getDefault().startActivity();，根据Binder机制可以知道getDefault其实叫做getProxy更好，得到的是ActivityManagerProxy，实际上就是先利用ServiceManager.getService("activity")得到BinderProxy（保持有底层的BpBinder，最终根据进程内的handle利用IPCThreadState来进行通信）然后放到了ActivityActivityManagerProxy.mRemote中，因此最终调用的是ActivityManagerNative的子类ActivityManagerService的onTransact函数中，即调用了ActivityManagerService的startActivity(arg0,...,arg9)。（Binder通信需要理解系统从下到上机制，以及Service的注册过程和时机）

ActivityManagerNative

120    @Override121    public boolean onTransact(int code, Parcel data, Parcel reply, int flags)122            throws RemoteException {123        switch (code) {124        case START_ACTIVITY_TRANSACTION:125        {126            data.enforceInterface(IActivityManager.descriptor);127            IBinder b = data.readStrongBinder();128            IApplicationThread app = ApplicationThreadNative.asInterface(b);129            String callingPackage = data.readString();130            Intent intent = Intent.CREATOR.createFromParcel(data);131            String resolvedType = data.readString();132            IBinder resultTo = data.readStrongBinder();133            String resultWho = data.readString();134            int requestCode = data.readInt();135            int startFlags = data.readInt();136            ProfilerInfo profilerInfo = data.readInt() != 0137                    ? ProfilerInfo.CREATOR.createFromParcel(data) : null;138            Bundle options = data.readInt() != 0139                    ? Bundle.CREATOR.createFromParcel(data) : null;140            int result = startActivity(app, callingPackage, intent, resolvedType,141                    resultTo, resultWho, requestCode, startFlags, profilerInfo, options);142            reply.writeNoException();143            reply.writeInt(result);144            return true;145        }复制代码

ActivityManagerService

3539    @Override3540    public final int startActivity(IApplicationThread caller, String callingPackage,3541            Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode,3542            int startFlags, ProfilerInfo profilerInfo, Bundle options) {3543        return startActivityAsUser(caller, callingPackage, intent, resolvedType, resultTo,3544            resultWho, requestCode, startFlags, profilerInfo, options,3545            UserHandle.getCallingUserId());3546    }复制代码

ActivityManagerService

3549    public final int startActivityAsUser(IApplicationThread caller, String callingPackage,3550            Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode,3551            int startFlags, ProfilerInfo profilerInfo, Bundle options, int userId) {3552        enforceNotIsolatedCaller("startActivity");3553        userId = handleIncomingUser(Binder.getCallingPid(), Binder.getCallingUid(), userId,3554                false, ALLOW_FULL_ONLY, "startActivity", null);3555        // TODO: Switch to user app stacks here.3556        return mStackSupervisor.startActivityMayWait(caller, -1, callingPackage, intent,3557                resolvedType, null, null, resultTo, resultWho, requestCode, startFlags,3558                profilerInfo, null, null, options, userId, null, null);3559    }复制代码

ActivityStackSupervisor

813    final int startActivityMayWait(IApplicationThread caller, int callingUid,814            String callingPackage, Intent intent, String resolvedType,815            IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,816            IBinder resultTo, String resultWho, int requestCode, int startFlags,817            ProfilerInfo profilerInfo, WaitResult outResult, Configuration config,818            Bundle options, int userId, IActivityContainer iContainer, TaskRecord inTask) {825        // Don't modify the client's object!826        intent = new Intent(intent);827828        // Collect information about the target of the Intent.829        ActivityInfo aInfo = resolveActivity(intent, resolvedType, startFlags,830                profilerInfo, userId);831832        ActivityContainer container = (ActivityContainer)iContainer;833        synchronized (mService) {834            final int realCallingPid = Binder.getCallingPid();835            final int realCallingUid = Binder.getCallingUid();846            final ActivityStack stack;847            if (container == null || container.mStack.isOnHomeDisplay()) {848                stack = getFocusedStack();849            } else {850                stack = container.mStack;851            }852            stack.mConfigWillChange = config != null853                    && mService.mConfiguration.diff(config) != 0;854            if (DEBUG_CONFIGURATION) Slog.v(TAG,855                    "Starting activity when config will change = " + stack.mConfigWillChange);856857            final long origId = Binder.clearCallingIdentity();926927            int res = startActivityLocked(caller, intent, resolvedType, aInfo,928                    voiceSession, voiceInteractor, resultTo, resultWho,929                    requestCode, callingPid, callingUid, callingPackage,930                    realCallingPid, realCallingUid, startFlags, options,931                    componentSpecified, null, container, inTask);932933            Binder.restoreCallingIdentity(origId);934978            return res;979        }980    }复制代码

关键函数在927行：startActivityLocked构造了ActivityRecord，然后调用startActivityUncheckedLocked

1272    final int startActivityLocked(IApplicationThread caller,1273            Intent intent, String resolvedType, ActivityInfo aInfo,1274            IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,1275            IBinder resultTo, String resultWho, int requestCode,1276            int callingPid, int callingUid, String callingPackage,1277            int realCallingPid, int realCallingUid, int startFlags, Bundle options,1278            boolean componentSpecified, ActivityRecord[] outActivity, ActivityContainer container,1279            TaskRecord inTask) {1280        int err = ActivityManager.START_SUCCESS;12811306        ActivityRecord sourceRecord = null;1307        ActivityRecord resultRecord = null;1318        ActivityStack resultStack = resultRecord == null ? null : resultRecord.task.stack;14301431        boolean abort = !mService.mIntentFirewall.checkStartActivity(intent, callingUid,1432                callingPid, resolvedType, aInfo.applicationInfo);14331434        if (mService.mController != null) {1435            try {1438                Intent watchIntent = intent.cloneFilter();1439                abort |= !mService.mController.activityStarting(watchIntent,1440                        aInfo.applicationInfo.packageName);1441            } catch (RemoteException e) {1442                mService.mController = null;1443            }1444        }1457        ActivityRecord r = new ActivityRecord(mService, callerApp, callingUid, callingPackage,1458                intent, resolvedType, aInfo, mService.mConfiguration, resultRecord, resultWho,1459                requestCode, componentSpecified, this, container, options);1460        if (outActivity != null) {1461            outActivity[0] = r;1462        }14631464        final ActivityStack stack = getFocusedStack();14891490        err = startActivityUncheckedLocked(r, sourceRecord, voiceSession, voiceInteractor,1491                startFlags, true, options, inTask);14921493        if (err < 0) 1498            notifyActivityDrawnForKeyguard();1499        }1500        return err;1501    }复制代码

看下startActivityUncheckedLocked函数，太长了，得继续撸代码

1574    final int startActivityUncheckedLocked(ActivityRecord r, ActivityRecord sourceRecord,1575            IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor, int startFlags,1576            boolean doResume, Bundle options, TaskRecord inTask) {1577        final Intent intent = r.intent;1578        final int callingUid = r.launchedFromUid;15881589        final boolean launchSingleTop = r.launchMode == ActivityInfo.LAUNCH_SINGLE_TOP;1590        final boolean launchSingleInstance = r.launchMode == ActivityInfo.LAUNCH_SINGLE_INSTANCE;1591        final boolean launchSingleTask = r.launchMode == ActivityInfo.LAUNCH_SINGLE_TASK;15921593        int launchFlags = intent.getFlags();16161617        final boolean launchTaskBehind = r.mLaunchTaskBehind1618                && !launchSingleTask && !launchSingleInstance1619                && (launchFlags & Intent.FLAG_ACTIVITY_NEW_DOCUMENT) != 0;1655        if (!doResume) {1656            r.delayedResume = true;1657        }16581659        ActivityRecord notTop =1660                (launchFlags & Intent.FLAG_ACTIVITY_PREVIOUS_IS_TOP) != 0 ? r : null;167617801781        boolean movedHome = false;1782        ActivityStack targetStack;17831784        intent.setFlags(launchFlags);178519721973        if (r.packageName != null) {1974            // If the activity being launched is the same as the one currently1975            // at the top, then we need to check if it should only be launched1976            // once.1977            ActivityStack topStack = getFocusedStack();1978            ActivityRecord top = topStack.topRunningNonDelayedActivityLocked(notTop);1979            if (top != null && r.resultTo == null) {1980                if (top.realActivity.equals(r.realActivity) && top.userId == r.userId) {1981                    if (top.app != null && top.app.thread != null) {1982                        if ((launchFlags & Intent.FLAG_ACTIVITY_SINGLE_TOP) != 01983                            || launchSingleTop || launchSingleTask) {1984                            ActivityStack.logStartActivity(EventLogTags.AM_NEW_INTENT, top,1985                                    top.task);1986                            // For paranoia, make sure we have correctly1987                            // resumed the top activity.1988                            topStack.mLastPausedActivity = null;1989                            if (doResume) {1990                                resumeTopActivitiesLocked();1991                            }1992                            ActivityOptions.abort(options);1993                            if ((startFlags&ActivityManager.START_FLAG_ONLY_IF_NEEDED) != 0) {1994                                // We don't need to start a new activity, and1995                                // the client said not to do anything if that1996                                // is the case, so this is it!1997                                return ActivityManager.START_RETURN_INTENT_TO_CALLER;1998                            }1999                            top.deliverNewIntentLocked(callingUid, r.intent);2000                            return ActivityManager.START_DELIVERED_TO_TOP;2001                        }2002                    }2003                }2004            }20052006        } else {2007            if (r.resultTo != null) {2008                r.resultTo.task.stack.sendActivityResultLocked(-1, r.resultTo, r.resultWho,2009                        r.requestCode, Activity.RESULT_CANCELED, null);2010            }2011            ActivityOptions.abort(options);2012            return ActivityManager.START_CLASS_NOT_FOUND;2013        }20142015        boolean newTask = false;2016        boolean keepCurTransition = false;20172018        TaskRecord taskToAffiliate = launchTaskBehind && sourceRecord != null ?2019                sourceRecord.task : null;20202166        mService.grantUriPermissionFromIntentLocked(callingUid, r.packageName,2167                intent, r.getUriPermissionsLocked(), r.userId);21682169        if (sourceRecord != null && sourceRecord.isRecentsActivity()) {2170            r.task.setTaskToReturnTo(RECENTS_ACTIVITY_TYPE);2171        }2172        if (newTask) {2173            EventLog.writeEvent(EventLogTags.AM_CREATE_TASK, r.userId, r.task.taskId);2174        }2175        ActivityStack.logStartActivity(EventLogTags.AM_CREATE_ACTIVITY, r, r.task);2176        targetStack.mLastPausedActivity = null;2177        targetStack.startActivityLocked(r, newTask, doResume, keepCurTransition, options);2178        if (!launchTaskBehind) {2179            // Don't set focus on an activity that's going to the back.2180            mService.setFocusedActivityLocked(r);2181        }2182        return ActivityManager.START_SUCCESS;2183    }复制代码

无法继续读下去了，还得准备下理论知识，不然只能最原始的通读所有代码，虽然也能完成阅读但是效率太低了！

参考：里面的调用关系有误

关注2177行，最终调用了targetStack.startActivityLocked

ActivityStack

1960    final void startActivityLocked(ActivityRecord r, boolean newTask,1961            boolean doResume, boolean keepCurTransition, Bundle options) {1962        TaskRecord rTask = r.task;1963        final int taskId = rTask.taskId;1964        // mLaunchTaskBehind tasks get placed at the back of the task stack.1965        if (!r.mLaunchTaskBehind && (taskForIdLocked(taskId) == null || newTask)) {1966            // Last activity in task had been removed or ActivityManagerService is reusing task.1967            // Insert or replace.1968            // Might not even be in.1969            insertTaskAtTop(rTask);1970            mWindowManager.moveTaskToTop(taskId);1971        }1972        TaskRecord task = null;2021        task = r.task;20222023        // Slot the activity into the history stack and proceed2024        if (DEBUG_ADD_REMOVE) Slog.i(TAG, "Adding activity " + r + " to stack to task " + task,2025                new RuntimeException("here").fillInStackTrace());2026        task.addActivityToTop(r);2027        task.setFrontOfTask();20282029        r.putInHistory();2030        if (!isHomeStack() || numActivities() > 0) {2034            boolean showStartingIcon = newTask;2035            ProcessRecord proc = r.app;2036            if (proc == null) {2037                proc = mService.mProcessNames.get(r.processName, r.info.applicationInfo.uid);2038            }2039            if (proc == null || proc.thread == null) {2040                showStartingIcon = true;2041            }2104        } else {2105            // If this is the first activity, don't do any fancy animations,2106            // because there is nothing for it to animate on top of.2107            mWindowManager.addAppToken(task.mActivities.indexOf(r), r.appToken,2108                    r.task.taskId, mStackId, r.info.screenOrientation, r.fullscreen,2109                    (r.info.flags & ActivityInfo.FLAG_SHOW_ON_LOCK_SCREEN) != 0, r.userId,2110                    r.info.configChanges, task.voiceSession != null, r.mLaunchTaskBehind);2111            ActivityOptions.abort(options);2112            options = null;2113        }2114        if (VALIDATE_TOKENS) {2115            validateAppTokensLocked();2116        }21172118        if (doResume) {2119            mStackSupervisor.resumeTopActivitiesLocked(this, r, options);2120        }2121    }复制代码

继续回到mStackSupervisor中resumeTopActivitiesLocked

2417    boolean resumeTopActivitiesLocked() {2418        return resumeTopActivitiesLocked(null, null, null);2419    }24202421    boolean resumeTopActivitiesLocked(ActivityStack targetStack, ActivityRecord target,2422            Bundle targetOptions) {2423        if (targetStack == null) {2424            targetStack = getFocusedStack();2425        }2426        // Do targetStack first.2427        boolean result = false;2428        if (isFrontStack(targetStack)) {2429            result = targetStack.resumeTopActivityLocked(target, targetOptions);2430        }2431        for (int displayNdx = mActivityDisplays.size() - 1; displayNdx >= 0; --displayNdx) {2432            final ArrayList
    
      stacks = mActivityDisplays.valueAt(displayNdx).mStacks;2433            for (int stackNdx = stacks.size() - 1; stackNdx >= 0; --stackNdx) {2434                final ActivityStack stack = stacks.get(stackNdx);2435                if (stack == targetStack) {2436                    // Already started above.2437                    continue;2438                }2439                if (isFrontStack(stack)) {2440                    stack.resumeTopActivityLocked(null);2441                }2442            }2443        }2444        return result;2445    }复制代码

ActivityStack

1470    final boolean resumeTopActivityLocked(ActivityRecord prev, Bundle options) {1471        if (inResumeTopActivity) {1472            // Don't even start recursing.1473            return false;1474        }14751476        boolean result = false;1477        try {1478            // Protect against recursion.1479            inResumeTopActivity = true;1480            result = resumeTopActivityInnerLocked(prev, options);1481        } finally {1482            inResumeTopActivity = false;1483        }1484        return result;1485    }复制代码

1487    final boolean resumeTopActivityInnerLocked(ActivityRecord prev, Bundle options) {1495        ActivityRecord parent = mActivityContainer.mParentActivity;15041505        // Find the first activity that is not finishing.1506        ActivityRecord next = topRunningActivityLocked(null);15071508        // Remember how we'll process this pause/resume situation, and ensure1509        // that the state is reset however we wind up proceeding.1510        final boolean userLeaving = mStackSupervisor.mUserLeaving;1511        mStackSupervisor.mUserLeaving = false;151215261527        next.delayedResume = false;15281592        // The activity may be waiting for stop, but that is no longer1593        // appropriate for it.1594        mStackSupervisor.mStoppingActivities.remove(next);1595        mStackSupervisor.mGoingToSleepActivities.remove(next);1596        next.sleeping = false;1597        mStackSupervisor.mWaitingVisibleActivities.remove(next);159816381639        // We need to start pausing the current activity so the top one1640        // can be resumed...1641        boolean dontWaitForPause = (next.info.flags&ActivityInfo.FLAG_RESUME_WHILE_PAUSING) != 0;1642        boolean pausing = mStackSupervisor.pauseBackStacks(userLeaving, true, dontWaitForPause);1643        if (mResumedActivity != null) {1644            pausing |= startPausingLocked(userLeaving, false, true, dontWaitForPause);1645            if (DEBUG_STATES) Slog.d(TAG, "resumeTopActivityLocked: Pausing " + mResumedActivity);1646        }17691770        ActivityStack lastStack = mStackSupervisor.getLastStack();1771        if (next.app != null && next.app.thread != null) {1772            if (DEBUG_SWITCH) Slog.v(TAG, "Resume running: " + next);17731774            // This activity is now becoming visible.1775            mWindowManager.setAppVisibility(next.appToken, true);19021903        } else {1904            // Whoops, need to restart this activity!1905            if (!next.hasBeenLaunched) {1906                next.hasBeenLaunched = true;1907            } else {1908                if (SHOW_APP_STARTING_PREVIEW) {1909                    mWindowManager.setAppStartingWindow(1910                            next.appToken, next.packageName, next.theme,1911                            mService.compatibilityInfoForPackageLocked(1912                                    next.info.applicationInfo),1913                            next.nonLocalizedLabel,1914                            next.labelRes, next.icon, next.logo, next.windowFlags,1915                            null, true);1916                }1917                if (DEBUG_SWITCH) Slog.v(TAG, "Restarting: " + next);1918            }1919            if (DEBUG_STATES) Slog.d(TAG, "resumeTopActivityLocked: Restarting " + next);1920            mStackSupervisor.startSpecificActivityLocked(next, true, true);1921        }19221923        if (DEBUG_STACK) mStackSupervisor.validateTopActivitiesLocked();1924        return true;1925    }复制代码

A. Activity.startActiviy(intent)    B. Instrumentation.execStartActivity    C. ActivityManagerNative.getDefault().startActivity(...)    D. ActivityManagerService ->  ActivityManagerNative.onTransact     E. ActivityManagerService.IActivityManager.startActivity    F. mStackSupervisor.startActivityMayWait ->  startActivityLocked    G. mStackSupervisor.startActivityUnchecked    G. targetStack.startActivityLocked    G. mStackSupervisor.resumeTopActivitiesLocked    G. mStackSupervisor.resumeTopActivityInnerLocked    G. targetStack.startPausingLocked复制代码

3.Activity首先执行pause流程

ActivityStack.startPausingLocked() IApplicationThread.schudulePauseActivity() ActivityThread.sendMessage() ActivityThread.H.sendMessage(); ActivityThread.H.handleMessage() ActivityThread.handlePauseActivity() ActivityThread.performPauseActivity() Activity.performPause() Activity.onPause() ActivityManagerNative.getDefault().activityPaused(token) ActivityManagerService.activityPaused() ActivityStack.activityPausedLocked() ActivityStack.completePauseLocked() ActivityStack.resumeTopActivitiesLocked() ActivityStack.resumeTopActivityLocked() ActivityStack.resumeTopActivityInnerLocked() ActivityStack.startSpecificActivityLocked复制代码

中间过程就不用细看了，基本上就是ActivityManagerService通过IApplicationThread将pause消息发给了ActivityThread，然后转到主线程H的handler中接收，通知Activity执行onPause并将通知ActivityManagerService已经处理onPause操作。ActivityManagerService要处理下ActivityStack的一些操作，这些还不是很清楚，最终要调用ActivityStatck.startSpecificActivityLocked开始启动进程了。

4.ActivityThread启动

ActivityStackSupervisor

1238    void startSpecificActivityLocked(ActivityRecord r,1239            boolean andResume, boolean checkConfig) {1240        1241        ProcessRecord app = mService.getProcessRecordLocked(r.processName,1242                r.info.applicationInfo.uid, true);12431244        r.task.stack.setLaunchTime(r);1245        // 进程已经启动了，且绑定了IApplicationThread1246        if (app != null && app.thread != null) {1247            try {1248                if ((r.info.flags&ActivityInfo.FLAG_MULTIPROCESS) == 01249                        || !"android".equals(r.info.packageName)) {1254                    app.addPackage(r.info.packageName, r.info.applicationInfo.versionCode,1255                            mService.mProcessStats);1256                }1257                realStartActivityLocked(r, app, andResume, checkConfig);1258                return;1259            } catch (RemoteException e) {1262            }1266        }1267        // 启动一个新的进程了哈1268        mService.startProcessLocked(r.processName, r.info.applicationInfo, true, 0,1269                "activity", r.intent.getComponent(), false, false, true);1270    }复制代码

ActivityManagerService

3076    private final void startProcessLocked(ProcessRecord app,3077            String hostingType, String hostingNameStr) {3078        startProcessLocked(app, hostingType, hostingNameStr, null /* abiOverride */,3079                null /* entryPoint */, null /* entryPointArgs */);3080    }30813082    private final void startProcessLocked(ProcessRecord app, String hostingType,3083            String hostingNameStr, String abiOverride, String entryPoint, String[] entryPointArgs){3097        mProcessesOnHold.remove(app);31023103        try {3104            int uid = app.uid;3106            int[] gids = null;3107            int mountExternal = Zygote.MOUNT_EXTERNAL_NONE;3189            boolean isActivityProcess = (entryPoint == null);3190            if (entryPoint == null) entryPoint = "android.app.ActivityThread";3191            checkTime(startTime, "startProcess: asking zygote to start proc");3192            Process.ProcessStartResult startResult = Process.start(entryPoint,3193                    app.processName, uid, uid, gids, debugFlags, mountExternal,3194                    app.info.targetSdkVersion, app.info.seinfo, requiredAbi, instructionSet,3195                    app.info.dataDir, entryPointArgs);3247            app.setPid(startResult.pid);3248            app.usingWrapper = startResult.usingWrapper;3249            app.removed = false;3250            app.killed = false;3251            app.killedByAm = false;3263        } catch (RuntimeException e) {3265            app.setPid(0);3271        }3272    }复制代码

此处创建了一个ProcessRecord！

Process

480    public static final ProcessStartResult start(final String processClass,481                                  final String niceName,482                                  int uid, int gid, int[] gids,483                                  int debugFlags, int mountExternal,484                                  int targetSdkVersion,485                                  String seInfo,486                                  String abi,487                                  String instructionSet,488                                  String appDataDir,489                                  String[] zygoteArgs) {490        try {491            return startViaZygote(processClass, niceName, uid, gid, gids,492                    debugFlags, mountExternal, targetSdkVersion, seInfo,493                    abi, instructionSet, appDataDir, zygoteArgs);494        } catch (ZygoteStartFailedEx ex) {495            Log.e(LOG_TAG,496                    "Starting VM process through Zygote failed");497            throw new RuntimeException(498                    "Starting VM process through Zygote failed", ex);499        }500    }复制代码

602    private static ProcessStartResult startViaZygote(final String processClass,603                                  final String niceName,604                                  final int uid, final int gid,605                                  final int[] gids,606                                  int debugFlags, int mountExternal,607                                  int targetSdkVersion,608                                  String seInfo,609                                  String abi,610                                  String instructionSet,611                                  String appDataDir,612                                  String[] extraArgs)613                                  throws ZygoteStartFailedEx {614        synchronized(Process.class) {615            ArrayList
    
      argsForZygote = new ArrayList
     
      ();616617            // --runtime-init, --setuid=, --setgid=,618            // and --setgroups= must go first619            argsForZygote.add("--runtime-init");620            argsForZygote.add("--setuid=" + uid);621            argsForZygote.add("--setgid=" + gid);642            argsForZygote.add("--target-sdk-version=" + targetSdkVersion);643646647            // --setgroups is a comma-separated list648            if (gids != null && gids.length > 0) {649                StringBuilder sb = new StringBuilder();650                sb.append("--setgroups=");651652                int sz = gids.length;653                for (int i = 0; i < sz; i++) {654                    if (i != 0) {655                        sb.append(',');656                    }657                    sb.append(gids[i]);658                }659660                argsForZygote.add(sb.toString());661            }662679            argsForZygote.add(processClass);680681            if (extraArgs != null) {682                for (String arg : extraArgs) {683                    argsForZygote.add(arg);684                }685            }686687            return zygoteSendArgsAndGetResult(openZygoteSocketIfNeeded(abi), argsForZygote);688        }689    }复制代码

695    private static ZygoteState openZygoteSocketIfNeeded(String abi) throws ZygoteStartFailedEx {696        if (primaryZygoteState == null || primaryZygoteState.isClosed()) {697            try {698                primaryZygoteState = ZygoteState.connect(ZYGOTE_SOCKET);699            } catch (IOException ioe) {700                throw new ZygoteStartFailedEx("Error connecting to primary zygote", ioe);701            }702        }703704        if (primaryZygoteState.matches(abi)) {705            return primaryZygoteState;706        }716717        if (secondaryZygoteState.matches(abi)) {718            return secondaryZygoteState;719        }722    }复制代码

536    private static ProcessStartResult zygoteSendArgsAndGetResult(537            ZygoteState zygoteState, ArrayList
    
      args)538            throws ZygoteStartFailedEx {539        try {550            final BufferedWriter writer = zygoteState.writer;551            final DataInputStream inputStream = zygoteState.inputStream;552553            writer.write(Integer.toString(args.size()));554            writer.newLine();555556            int sz = args.size();557            for (int i = 0; i < sz; i++) {558                String arg = args.get(i);559                if (arg.indexOf('\n') >= 0) {562                }563                writer.write(arg);564                writer.newLine();565            }566567            writer.flush();568569            // Should there be a timeout on this?570            ProcessStartResult result = new ProcessStartResult();571            result.pid = inputStream.readInt();575            result.usingWrapper = inputStream.readBoolean();576            return result;577        } catch (IOException ex) {578            zygoteState.close();579            throw new ZygoteStartFailedEx(ex);580        }581    }复制代码

最终让Zygote的socket启动了android.app.ActivityThread进程，并执行了main函数，并返回了pid。

5.ActivityThread完成Activity的启动

ActivityManagerService.startProcessLocked() Process.start() ActivityThread.main() ActivityThread.attach() ActivityManagerNative.getDefault().attachApplication() ActivityManagerService.attachApplication() 复制代码

ActivityThread

5184    public static void main(String[] args) {52045205        Looper.prepareMainLooper();52065207        ActivityThread thread = new ActivityThread();5208        thread.attach(false);5214        AsyncTask.init();52155221        Looper.loop();5224    }5225}复制代码

分析几个关键的成员变量

mH：作用很简单即将ApplicationThread线程转到主线程中处理

mAppThread：ApplicationThread主要用来接收ActivityManagerService消息

mActivities：ArrayMap<IBinder, ActivityClientRecord>一个map，用来记录ActivityRecord成员变量IApplicationToken.Stub appToken

ActivityThread ------------>IApplicationToken------------> ActivityManagerService

<------------IApplicationThread<-----------复制代码

问题：token什么时候传入ActivityThread的，下面似乎能找到答案，先将IApplicationThread传入ActivityManagerService中attchApplication，利用IApplicationThread就能传token到ActivityThread中了。

ActivityThread

5041    private void attach(boolean system) {5042        sCurrentActivityThread = this;5043        mSystemThread = system;5044        if (!system) {5053            RuntimeInit.setApplicationObject(mAppThread.asBinder());5054            final IActivityManager mgr = ActivityManagerNative.getDefault();5055            try {5055                // 此处开始在ActivityManagerService执行初始化操作5056                mgr.attachApplication(mAppThread);5057            } catch (RemoteException ex) {5059            }5081        } else {5086            try {5055                // 传入的是false，因此应用的启动不会走这里5092            } catch (Exception e) {5095            }5096        }5127    }复制代码

ActivityManagerService

6249    @Override6250    public final void attachApplication(IApplicationThread thread) {6251        synchronized (this) {6252            int callingPid = Binder.getCallingPid();6253            final long origId = Binder.clearCallingIdentity();6254            attachApplicationLocked(thread, callingPid);6255            Binder.restoreCallingIdentity(origId);6256        }6257    }复制代码

6029    private final boolean attachApplicationLocked(IApplicationThread thread,6030            int pid) {60316035        ProcessRecord app;6036        if (pid != MY_PID && pid >= 0) {6037            synchronized (mPidsSelfLocked) {6038                app = mPidsSelfLocked.get(pid);6039            }6040        } else {6041            app = null;6042        }6072        final String processName = app.processName;6086        app.makeActive(thread, mProcessStats);6087        app.curAdj = app.setAdj = -100;6088        app.curSchedGroup = app.setSchedGroup = Process.THREAD_GROUP_DEFAULT;6089        app.forcingToForeground = null;6090        updateProcessForegroundLocked(app, false, false);6091        app.hasShownUi = false;6092        app.debugging = false;6093        app.cached = false;60966097        boolean normalMode = mProcessesReady || isAllowedWhileBooting(app.info);6098        List
    
      providers = normalMode ? generateApplicationProvidersLocked(app) : null;60996107        try {6152            ApplicationInfo appInfo = app.instrumentationInfo != null6153                    ? app.instrumentationInfo : app.info;6160            thread.bindApplication(processName, appInfo, providers, app.instrumentationClass,6161                    profilerInfo, app.instrumentationArguments, app.instrumentationWatcher,6162                    app.instrumentationUiAutomationConnection, testMode, enableOpenGlTrace,6163                    isRestrictedBackupMode || !normalMode, app.persistent,6164                    new Configuration(mConfiguration), app.compat, getCommonServicesLocked(),6165                    mCoreSettingsObserver.getCoreSettingsLocked());6166            updateLruProcessLocked(app, false, null);6168        } catch (Exception e) {6174            app.resetPackageList(mProcessStats);6175            app.unlinkDeathRecipient();6176            startProcessLocked(app, "bind fail", processName);6177            return false;6178        }61796186        boolean badApp = false;6187        boolean didSomething = false;61886189        // See if the top visible activity is waiting to run in this process...6190        if (normalMode) {6191            try {6192                if (mStackSupervisor.attachApplicationLocked(app)) {6193                    didSomething = true;6194                }6195            } catch (Exception e) {6197                badApp = true;6198            }6199        }62006201        // Find any services that should be running in this process...6202        if (!badApp) {6203            try {6204                didSomething |= mServices.attachApplicationLocked(app, processName);6205            } catch (Exception e) {6206                Slog.wtf(TAG, "Exception thrown starting services in " + app, e);6207                badApp = true;6208            }6209        }62456246        return true;6247    }复制代码

第一步：调用了IApplicationThread的bindApplication

其中ApplicationInfo是在startProcessLocked是创建ProcessRecord时构建的，创建了一个AppBindData数据结构，并调用了复制代码

739        public final void bindApplication(String processName, ApplicationInfo appInfo,740                List
    
      providers, ComponentName instrumentationName,741                ProfilerInfo profilerInfo, Bundle instrumentationArgs,742                IInstrumentationWatcher instrumentationWatcher,743                IUiAutomationConnection instrumentationUiConnection, int debugMode,744                boolean enableOpenGlTrace, boolean isRestrictedBackupMode, boolean persistent,745                Configuration config, CompatibilityInfo compatInfo, Map
     
       services,746                Bundle coreSettings) {747748            if (services != null) {749                // 似乎就三个提前存储的：package、window、alarm750                ServiceManager.initServiceCache(services);751            }791792            AppBindData data = new AppBindData();793            data.processName = processName;794            data.appInfo = appInfo;795            data.providers = providers;796            data.instrumentationName = instrumentationName;797            data.instrumentationArgs = instrumentationArgs;798            data.instrumentationWatcher = instrumentationWatcher;799            data.instrumentationUiAutomationConnection = instrumentationUiConnection;800            data.debugMode = debugMode;801            data.enableOpenGlTrace = enableOpenGlTrace;802            data.restrictedBackupMode = isRestrictedBackupMode;803            data.persistent = persistent;804            data.config = config;805            data.compatInfo = compatInfo;806            data.initProfilerInfo = profilerInfo;807            sendMessage(H.BIND_APPLICATION, data);808        }复制代码

转到主线程中处理handleBindApplication，构造了一个ContextIpl，

4254    private void handleBindApplication(AppBindData data) {4255        mBoundApplication = data;4256        mConfiguration = new Configuration(data.config);4257        mCompatConfiguration = new Configuration(data.config);4259        mProfiler = new Profiler();42844289        if (data.appInfo.targetSdkVersion <= android.os.Build.VERSION_CODES.HONEYCOMB_MR1) {4290            AsyncTask.setDefaultExecutor(AsyncTask.THREAD_POOL_EXECUTOR);4291        }4317        // 1.创建new LoadedApk(4317        data.info = getPackageInfoNoCheck(data.appInfo, data.compatInfo);4317        4329        final ContextImpl appContext = ContextImpl.createAppContext(this, data.info);4420        // 这里加一个判断还是很费解的，两个分支逻辑基本一样，所以任选一条分析4421        if (data.instrumentationName != null) {4422            InstrumentationInfo ii = null;4423            try {4424                ii = appContext.getPackageManager().4425                    getInstrumentationInfo(data.instrumentationName, 0);4426            } catch (PackageManager.NameNotFoundException e) {4427            }4442            ApplicationInfo instrApp = new ApplicationInfo();4443            instrApp.packageName = ii.packageName;4444            instrApp.sourceDir = ii.sourceDir;4445            instrApp.publicSourceDir = ii.publicSourceDir;4446            instrApp.splitSourceDirs = ii.splitSourceDirs;4447            instrApp.splitPublicSourceDirs = ii.splitPublicSourceDirs;4448            instrApp.dataDir = ii.dataDir;4449            instrApp.nativeLibraryDir = ii.nativeLibraryDir;4450            LoadedApk pi = getPackageInfo(instrApp, data.compatInfo,4451                    appContext.getClassLoader(), false, true, false);4452            ContextImpl instrContext = ContextImpl.createAppContext(this, pi);44534454            try {4455                java.lang.ClassLoader cl = instrContext.getClassLoader();4456                mInstrumentation = (Instrumentation)4457                    cl.loadClass(data.instrumentationName.getClassName()).newInstance();4458            } catch (Exception e) {4462            }44634464            mInstrumentation.init(this, instrContext, appContext,4465                   new ComponentName(ii.packageName, ii.name), data.instrumentationWatcher,4466                   data.instrumentationUiAutomationConnection);4476        } else {4476             // 2.创建new Instrumentation(4477            mInstrumentation = new Instrumentation();4478        }44794488        try {4488             // 3.创建了Application对象，并调用了attachBaseContext4491            Application app = data.info.makeApplication(data.restrictedBackupMode, null);4492            mInitialApplication = app;4496            if (!data.restrictedBackupMode) {4497                List
    
      providers = data.providers;4498                if (providers != null) {4499             // 3.安装进程中携带的Providers4499                    installContentProviders(app, providers);4502                    mH.sendEmptyMessageDelayed(H.ENABLE_JIT, 10*1000);4503                }4504            }4508            mInstrumentation.onCreate(data.instrumentationArgs); // 没什么用4508             // 4.调用了application的onCreate操作4518            mInstrumentation.callApplicationOnCreate(app);4526        } finally {4528        }4529    }4530复制代码

这段代码里面的分支条件有点头晕，总之穿件了一个LoadedApk、Instrumentation、Application、ContextImpl。其中Application有LoadedApk.makeApplication构建的，最终由Instrmentation.newApplication构建，即调用了Application构造方法，并attach了ContextImpl，由此可见Application在attachBaseContext的时候输入的是这里的ContextImpl。这里得注意一下，Provider的安装是在Application的attachBaseContext和onCreate之间的。

LoadedApk

539    public Application makeApplication(boolean forceDefaultAppClass,540            Instrumentation instrumentation) {541        if (mApplication != null) {542            return mApplication;543        }544545        Application app = null;547        String appClass = mApplicationInfo.className;551552        try {553            java.lang.ClassLoader cl = getClassLoader();557            ContextImpl appContext = ContextImpl.createAppContext(mActivityThread, this);558            app = mActivityThread.mInstrumentation.newApplication(559                    cl, appClass, appContext);560            appContext.setOuterContext(app);561        } catch (Exception e) {567        }568        mActivityThread.mAllApplications.add(app);569        mApplication = app;594        }595596        return app;597    }复制代码

第二步：调用了mStackSupervisor.attachApplicationLocked(app)

ActivityStackSupervisor.attachApplicationLocked() ActivityStackSupervisor.realStartActivityLocked() IApplicationThread.scheduleLauncherActivity() ActivityThread.sendMessage() ActivityThread.H.sendMessage() ActivityThread.H.handleMessage() ActivityThread.handleLauncherActivity() ActivityThread.performLauncherActivity() Instrumentation.callActivityOnCreate() Activity.onCreate() ActivityThread.handleResumeActivity() ActivityThread.performResumeActivity() Activity.performResume() Instrumentation.callActivityOnResume() Activity.onResume() ActivityManagerNative.getDefault().activityResumed(token) 复制代码

511    boolean attachApplicationLocked(ProcessRecord app) throws RemoteException {512        final String processName = app.processName;513        boolean didSomething = false;514        for (int displayNdx = mActivityDisplays.size() - 1; displayNdx >= 0; --displayNdx) {515            ArrayList
    
      stacks = mActivityDisplays.valueAt(displayNdx).mStacks;516            for (int stackNdx = stacks.size() - 1; stackNdx >= 0; --stackNdx) {517                final ActivityStack stack = stacks.get(stackNdx);518                if (!isFrontStack(stack)) {519                    continue;520                }521                ActivityRecord hr = stack.topRunningActivityLocked(null);522                if (hr != null) {523                    if (hr.app == null && app.uid == hr.info.applicationInfo.uid524                            && processName.equals(hr.processName)) {525                        try {526                            if (realStartActivityLocked(hr, app, true, true)) {527                                didSomething = true;528                            }529                        } catch (RemoteException e) {532                            throw e;533                        }534                    }535                }536            }537        }538        if (!didSomething) {539            ensureActivitiesVisibleLocked(null, 0);540        }541        return didSomething;542    }复制代码

1061    final boolean realStartActivityLocked(ActivityRecord r,1062            ProcessRecord app, boolean andResume, boolean checkConfig)1063            throws RemoteException {106410841085        r.app = app;1086        app.waitingToKill = null;1087        r.launchCount++;1088        r.lastLaunchTime = SystemClock.uptimeMillis();10981099        final ActivityStack stack = r.task.stack;1100        try {1104            List
    
      results = null;1105            List
     
       newIntents = null;1106            if (andResume) {1107                results = r.results;1108                newIntents = r.newIntents;1109            }11521156            app.forceProcessStateUpTo(ActivityManager.PROCESS_STATE_TOP);1157            app.thread.scheduleLaunchActivity(new Intent(r.intent), r.appToken,1158                    System.identityHashCode(r), r.info, new Configuration(mService.mConfiguration),1159                    r.compat, r.task.voiceInteractor, app.repProcState, r.icicle, r.persistentState,1160                    results, newIntents, !andResume, mService.isNextTransitionForward(),1161                    profilerInfo);11621183        } catch (RemoteException e) {1200        }1235        return true;1236    }复制代码

2343    private void handleLaunchActivity(ActivityClientRecord r, Intent customIntent) {23482360        Activity a = performLaunchActivity(r, customIntent);23612362        if (a != null) {2363            r.createdConfig = new Configuration(mConfiguration);2364            Bundle oldState = r.state;2365            handleResumeActivity(r.token, false, r.isForward,2366                    !r.activity.mFinished && !r.startsNotResumed);23672368            if (!r.activity.mFinished && r.startsNotResumed) {2378                try {2379                    r.activity.mCalled = false;2380                    mInstrumentation.callActivityOnPause(r.activity);2388                    if (r.isPreHoneycomb()) {2389                        r.state = oldState;2390                    }23962397                } catch (SuperNotCalledException e) {2398                    throw e;23992400                } catch (Exception e) {2407                }2408                r.paused = true;2409            }2410        } else {2419        }2420    }复制代码

首先调用了performLaunchActivity，而后调用了handleResumeActivity，分别看看这两个关键函数吧：

2175    private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {21772178        ActivityInfo aInfo = r.activityInfo;21952196        Activity activity = null;2197        try {2198            java.lang.ClassLoader cl = r.packageInfo.getClassLoader();2198            // 1.利用mIntrumentation创建了一个Activity2199            activity = mInstrumentation.newActivity(2200                    cl, component.getClassName(), r.intent);2207        } catch (Exception e) {2213        }22142215        try {2216            Application app = r.packageInfo.makeApplication(false, mInstrumentation);22252226            if (activity != null) {2226            // 2.创建了一个ContextImpl并对Activity执行了attach操作2227                Context appContext = createBaseContextForActivity(r, activity);2232                activity.attach(appContext, this, getInstrumentation(), r.token,2233                        r.ident, app, r.intent, r.activityInfo, title, r.parent,2234                        r.embeddedID, r.lastNonConfigurationInstances, config,2235                        r.voiceInteractor);2242                int theme = r.activityInfo.getThemeResource();2243                if (theme != 0) {2244                    activity.setTheme(theme);2245                }22462247                activity.mCalled = false;2247            // 3.调用了Activity的onCreate操作2248                if (r.isPersistable()) {2249                    mInstrumentation.callActivityOnCreate(activity, r.state, r.persistentState);2250                } else {2251                    mInstrumentation.callActivityOnCreate(activity, r.state);2252                }2258                r.activity = activity;2260                if (!r.activity.mFinished) {2260            // 3.调用了Activity的onStart操作2261                    activity.performStart();2262                    r.stopped = false;2263                }2264                if (!r.activity.mFinished) {2265                    if (r.isPersistable()) {2266                        if (r.state != null || r.persistentState != null) {2267                            mInstrumentation.callActivityOnRestoreInstanceState(activity, r.state,2268                                    r.persistentState);2269                        }2270                    } else if (r.state != null) {2271                        mInstrumentation.callActivityOnRestoreInstanceState(activity, r.state);2272                    }2273                }2288            }2289            r.paused = true;22902291            mActivities.put(r.token, r);22922293        } catch (SuperNotCalledException e) {2294            throw e;22952296        } catch (Exception e) {2302        }23032304        return activity;2305    }复制代码

总结一下performLauncheActivity即是创建了一个Activity，执行了attach(ContextImpl)，执行了onCreate操作、执行了onStart操作。

2974    final void handleResumeActivity(IBinder token,2975            boolean clearHide, boolean isForward, boolean reallyResume) {2982        // 1.调用了Activity的onResume操作2982        ActivityClientRecord r = performResumeActivity(token, clearHide);29832984        if (r != null) {2985            final Activity a = r.activity;298630313034            if (!r.activity.mFinished && willBeVisible3035                    && r.activity.mDecor != null && !r.hideForNow) {3058                r.activity.mVisibleFromServer = true;3059                mNumVisibleActivities++;3060                if (r.activity.mVisibleFromClient) {3061                    r.activity.makeVisible();3062                }3063            }30643065            if (!r.onlyLocalRequest) {3066                r.nextIdle = mNewActivities;3067                mNewActivities = r;3067                // 2.前一个栈顶Activity的onPause操作3070                Looper.myQueue().addIdleHandler(new Idler());3071            }3072            r.onlyLocalRequest = false;30733075            if (reallyResume) {3076                try {3077                    // 3.通知一下Activity已经onResume了3077                    ActivityManagerNative.getDefault().activityResumed(token);3078                } catch (RemoteException ex) {3079                }3080            }3082        } else {3090        }3091    }复制代码

第三步：调用了mServices.attachApplicationLocked 与服务的启动相关，这里暂时不考虑了。

6.Activity执行的onStop流程

Looper.myQueue().addIdleHandler(new Idler()) Idler.queueIdle() ActivityManagerNative.getDefault().activityIdle() ActivityManagerService.activityIdle() ActivityStackSupervisor.activityIdleInternalLocked() ActivityStack.stopActivityLocked() IApplicationThread.scheduleStopActivity() ActivityThread.scheduleStopActivity() ActivityThread.sendMessage() ActivityThread.H.sendMessage() ActivityThread.H.handleMessage() ActivityThread.handleStopActivity() ActivityThread.performStopActivityInner() ActivityThread.callCallActivityOnSaveInstanceState() Instrumentation.callActivityOnSaveInstanceState() Activity.performSaveInstanceState() Activity.onSaveInstanceState() Activity.performStop() Instrumentation.callActivityOnStop() Activity.onStop() 复制代码

3070                Looper.myQueue().addIdleHandler(new Idler());复制代码

1525    private class Idler implements MessageQueue.IdleHandler {1526        @Override1527        public final boolean queueIdle() {1528            ActivityClientRecord a = mNewActivities;1529            boolean stopProfiling = false;1530            if (mBoundApplication != null && mProfiler.profileFd != null1531                    && mProfiler.autoStopProfiler) {1532                stopProfiling = true;1533            }1534            if (a != null) {1535                mNewActivities = null;1536                IActivityManager am = ActivityManagerNative.getDefault();1537                ActivityClientRecord prev;1538                do {1543                    if (a.activity != null && !a.activity.mFinished) {1544                        try {1545                            am.activityIdle(a.token, a.createdConfig, stopProfiling);1546                            a.createdConfig = null;1547                        } catch (RemoteException ex) {1548                            // Ignore1549                        }1550                    }1551                    prev = a;1552                    a = a.nextIdle;1553                    prev.nextIdle = null;1554                } while (a != null);1555            }1560            return false;1561        }1562    }复制代码

2214    final ActivityRecord activityIdleInternalLocked(final IBinder token, boolean fromTimeout, Configuration config) {2218        ArrayList
    
      stops = null;2219        ArrayList
     
       finishes = null;2220        ArrayList
      
        startingUsers = null;2221        int NS = 0;2222        int NF = 0;2223        boolean booting = false;2224        boolean enableScreen = false;2225        boolean activityRemoved = false;22262227        ActivityRecord r = ActivityRecord.forToken(token);2228        if (r != null) {2248            r.idle = true;22492290        // Stop any activities that are scheduled to do so but have been2291        // waiting for the next one to start.2292        for (int i = 0; i < NS; i++) {2293            r = stops.get(i);2294            final ActivityStack stack = r.task.stack;2295            if (r.finishing) {2296                stack.finishCurrentActivityLocked(r, ActivityStack.FINISH_IMMEDIATELY, false);2297            } else {2298                stack.stopActivityLocked(r);2299            }2300        }2338        return r;2339    }复制代码

2513    final void stopActivityLocked(ActivityRecord r) {25302531        if (r.app != null && r.app.thread != null) {2532            adjustFocusedActivityLocked(r);2533            r.resumeKeyDispatchingLocked();2534            try {2535                r.stopped = false;2541                if (!r.visible) {2542                    mWindowManager.setAppVisibility(r.appToken, false);2543                }2544                r.app.thread.scheduleStopActivity(r.appToken, r.visible, r.configChangeFlags);2550            } catch (Exception e) {2562            }2563        }2564    }复制代码

3385    private void handleStopActivity(IBinder token, boolean show, int configChanges) {3386        ActivityClientRecord r = mActivities.get(token);3387        r.activity.mConfigChangeFlags |= configChanges;33883389        StopInfo info = new StopInfo();3390        performStopActivityInner(r, info, show, true);33973399        if (!r.isPreHoneycomb()) {3400            QueuedWork.waitToFinish();3401        }3408        info.activity = r;3409        info.state = r.state;3410        info.persistentState = r.persistentState;3411        mH.post(info);3412        mSomeActivitiesChanged = true;3413    }复制代码

3298    private void performStopActivityInner(ActivityClientRecord r,3299            StopInfo info, boolean keepShown, boolean saveState) {3300        if (localLOGV) Slog.v(TAG, "Performing stop of " + r);3301        if (r != null) {3331            // Next have the activity save its current state and managed dialogs...3332            if (!r.activity.mFinished && saveState) {3333                if (r.state == null) {3334                    callCallActivityOnSaveInstanceState(r);3335                }3336            }33373338            if (!keepShown) {3339                try {3340                    // Now we are idle.3341                    r.activity.performStop();3342                } catch (Exception e) {3349                }3350                r.stopped = true;3351            }33523353            r.paused = true;3354        }3355    }复制代码

首先调用的onSaveInstanceState，其次调用了performStop操作，至此Activity的启动的什么周期都走完了。

7.启动进程已存在的Activity

ActivityStackSupervisor

1238    void startSpecificActivityLocked(ActivityRecord r,1239            boolean andResume, boolean checkConfig) {1240        1241        ProcessRecord app = mService.getProcessRecordLocked(r.processName,1242                r.info.applicationInfo.uid, true);12431244        r.task.stack.setLaunchTime(r);1245        // 进程已经启动了，且绑定了IApplicationThread1246        if (app != null && app.thread != null) {1247            try {1248                if ((r.info.flags&ActivityInfo.FLAG_MULTIPROCESS) == 01249                        || !"android".equals(r.info.packageName)) {1254                    app.addPackage(r.info.packageName, r.info.applicationInfo.versionCode,1255                            mService.mProcessStats);1256                }1257                realStartActivityLocked(r, app, andResume, checkConfig);1258                return;1259            } catch (RemoteException e) {1262            }1266        }1267        // 启动一个新的进程了哈1268        mService.startProcessLocked(r.processName, r.info.applicationInfo, true, 0,1269                "activity", r.intent.getComponent(), false, false, true);1270    }复制代码

这是贴的前面的代码，如果进程已经启动了，即ProcessRecord和IApplicationThread都存在，那么就调用realStartActivityLocked直接启动Activity了。

8.总结：

1.生命周期

原始Activity A -> onPause -> onStop

目标Activity B -> onCreate -> onStart -> onResume

2.应用的启动过程

startActivity -> startActivityForReuslt -> execStartActivity -> ActivityManagerService.execStartActivity -> ... -> 创建一个ActivityRecord、创建应用进程，进程创建之后 -> ActivityThread启动 -> bindApplication -> 绑定完成之后看是否需要启动Activity -> handleLauncheActivity -> handleResumeActivity -> Looper.getQueue().addIdleHandler() -> handleStopActivity -> end

参考：《Android源码解析之-->Activity启动流程》