Android8.1源码讲解之ActivityThread启动Activity

在上一篇文章有说ActivityThread启动的过程，最后讲解到ActivityThread的main函数启动。这篇文章接上篇文章讲解main方法中怎么启动Activity的，方便日后讲解有关Activity中的事件处理机制。

一、ActivityThread中main方法

public static void main(String[] args) {
    SamplingProfilerIntegration.start();

    // CloseGuard defaults to true and can be quite spammy.  We
    // disable it here, but selectively enable it later (via
    // StrictMode) on debug builds, but using DropBox, not logs.
    CloseGuard.setEnabled(false);

    Environment.initForCurrentUser();

    // Set the reporter for event logging in libcore
    EventLogger.setReporter(new EventLoggingReporter());

    Process.setArgV0("");

    //准备主线程中的Loop启动
    Looper.prepareMainLooper();
    //创建ActivityThread实例
    ActivityThread thread = new ActivityThread();
    //ActivityThread内容绑定
    thread.attach(false);

    if (sMainThreadHandler == null) {//获取主线程中的Handler
        sMainThreadHandler = thread.getHandler();
    }

    AsyncTask.init();

    if (false) {
        Looper.myLooper().setMessageLogging(new
                LogPrinter(Log.DEBUG, "ActivityThread"));
    }
    //启动主线中的Handler消息机制的loop
    Looper.loop();

    throw new RuntimeException("Main thread loop unexpectedly exited");
}

这里完成了ActivityThread的实例的创建，然后进行绑定操作。在这里还完成了主线程也就是UI中的looper的启动，以便日后使用Handler消息机制。接下来要看一下ActivityThread的绑定Application的过程，接下来看一下ActivityThread中的attach方法。

//在这里是启动的ActivityThread不是系统,在main方法中已经看到传递过来的是false
private void attach(boolean system) {
    sThreadLocal.set(this);
    mSystemThread = system;
    if (!system) {
        ViewRootImpl.addFirstDrawHandler(new Runnable() {
            public void run() {
                ensureJitEnabled();
            }
        });
        android.ddm.DdmHandleAppName.setAppName("",
                UserHandle.myUserId());
        RuntimeInit.setApplicationObject(mAppThread.asBinder());
        //获取远程AMS的代理对象
        IActivityManager mgr = ActivityManagerNative.getDefault();
        //调用AMS中attachApplication方法，mAppThread在类加载的时候已经进行了初始化
        //在以后Activity的start、stop、resume以及显示都是mAppThread进行的
        try {
            mgr.attachApplication(mAppThread);
        } catch (RemoteException ex) {
            // Ignore
        }
    } else {
        // Don't set application object here -- if the system crashes,
        // we can't display an alert, we just want to die die die.
        android.ddm.DdmHandleAppName.setAppName("system_process",
                UserHandle.myUserId());
        try {
            mInstrumentation = new Instrumentation();
            ContextImpl context = new ContextImpl();
            context.init(getSystemContext().mPackageInfo, null, this);
            Application app = Instrumentation.newApplication(Application.class, context);
            mAllApplications.add(app);
            mInitialApplication = app;
            app.onCreate();
        } catch (Exception e) {
            throw new RuntimeException(
                    "Unable to instantiate Application():" + e.toString(), e);
        }
    }

    // add dropbox logging to libcore
    DropBox.setReporter(new DropBoxReporter());

    ViewRootImpl.addConfigCallback(new ComponentCallbacks2() {
        public void onConfigurationChanged(Configuration newConfig) {
            synchronized (mPackages) {
                // We need to apply this change to the resources
                // immediately, because upon returning the view
                // hierarchy will be informed about it.
                if (applyConfigurationToResourcesLocked(newConfig, null)) {
                    // This actually changed the resources!  Tell
                    // everyone about it.
                    if (mPendingConfiguration == null ||
                            mPendingConfiguration.isOtherSeqNewer(newConfig)) {
                        mPendingConfiguration = newConfig;

                        queueOrSendMessage(H.CONFIGURATION_CHANGED, newConfig);
                    }
                }
            }
        }
        public void onLowMemory() {
        }
        public void onTrimMemory(int level) {
        }
    });
}

在这里获取到远程AMS的代理对象，然后调用AMS方法进行Application的绑定工作。在这里有说到mAppThread这个成员变量，是ApplicationThreadNative的实例，在以后的操作Activity的操作都是在ApplicationThreadNative中进行的，这里不在详说。接下来就又回到了AMS中。

二、AMS中attachApplication

1、AMS的attachApplication

@Override
public final 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) {

    // Find the application record that is being attached...  either via
    // the pid if we are running in multiple processes, or just pull the
    // next app record if we are emulating process with anonymous threads.
    ProcessRecord app;
    long startTime = SystemClock.uptimeMillis();
    if (pid != MY_PID && pid >= 0) {
        synchronized (mPidsSelfLocked) {
            //由pid获取进程记录
            app = mPidsSelfLocked.get(pid);
        }
    } else {
        app = null;
    }

    if (app == null) {//如果不存在则做相应处理
        Slog.w(TAG, "No pending application record for pid " + pid
                + " (IApplicationThread " + thread + "); dropping process");
        EventLog.writeEvent(EventLogTags.AM_DROP_PROCESS, pid);
        if (pid > 0 && pid != MY_PID) {
            killProcessQuiet(pid);
            //TODO: killProcessGroup(app.info.uid, pid);
        } else {
            try {
                thread.scheduleExit();
            } catch (Exception e) {
                // Ignore exceptions.
            }
        }
        return false;
    }

    // If this application record is still attached to a previous
    // process, clean it up now.
    //如果当前进程记录已经和其他应用进程绑定了这里进行删除操作
    if (app.thread != null) {
        handleAppDiedLocked(app, true, true);
    }

    // Tell the process all about itself.

    if (DEBUG_ALL) Slog.v(
            TAG, "Binding process pid " + pid + " to record " + app);

    final String processName = app.processName;
    try {
        AppDeathRecipient adr = new AppDeathRecipient(
                app, pid, thread);
        thread.asBinder().linkToDeath(adr, 0);
        app.deathRecipient = adr;
    } catch (RemoteException e) {
        app.resetPackageList(mProcessStats);
        startProcessLocked(app, "link fail", processName);
        return false;
    }

    EventLog.writeEvent(EventLogTags.AM_PROC_BOUND, app.userId, app.pid, app.processName);

    app.makeActive(thread, mProcessStats);
    app.curAdj = app.setAdj = app.verifiedAdj = ProcessList.INVALID_ADJ;
    app.curSchedGroup = app.setSchedGroup = ProcessList.SCHED_GROUP_DEFAULT;
    app.forcingToImportant = null;
    updateProcessForegroundLocked(app, false, false);
    app.hasShownUi = false;
    app.debugging = false;
    app.cached = false;
    app.killedByAm = false;
    app.killed = false;


    ......
    忽略部分代码

        checkTime(startTime, "attachApplicationLocked: immediately before bindApplication");
        mStackSupervisor.mActivityMetricsLogger.notifyBindApplication(app);
        //对Activity中的相关信息进行绑定
        if (app.instr != null) {
            thread.bindApplication(processName, appInfo, providers,
                    app.instr.mClass,
                    profilerInfo, app.instr.mArguments,
                    app.instr.mWatcher,
                    app.instr.mUiAutomationConnection, testMode,
                    mBinderTransactionTrackingEnabled, enableTrackAllocation,
                    isRestrictedBackupMode || !normalMode, app.persistent,
                    new Configuration(getGlobalConfiguration()), app.compat,
                    getCommonServicesLocked(app.isolated),
                    mCoreSettingsObserver.getCoreSettingsLocked(),
                    buildSerial);
        } else {
            thread.bindApplication(processName, appInfo, providers, null, profilerInfo,
                    null, null, null, testMode,
                    mBinderTransactionTrackingEnabled, enableTrackAllocation,
                    isRestrictedBackupMode || !normalMode, app.persistent,
                    new Configuration(getGlobalConfiguration()), app.compat,
                    getCommonServicesLocked(app.isolated),
                    mCoreSettingsObserver.getCoreSettingsLocked(),
                    buildSerial);
        }

        checkTime(startTime, "attachApplicationLocked: immediately after bindApplication");
        updateLruProcessLocked(app, false, null);
        checkTime(startTime, "attachApplicationLocked: after updateLruProcessLocked");
        app.lastRequestedGc = app.lastLowMemory = SystemClock.uptimeMillis();
    } catch (Exception e) {
        // todo: Yikes!  What should we do?  For now we will try to
        // start another process, but that could easily get us in
        // an infinite loop of restarting processes...
        Slog.wtf(TAG, "Exception thrown during bind of " + app, e);

        app.resetPackageList(mProcessStats);
        app.unlinkDeathRecipient();
        startProcessLocked(app, "bind fail", processName);
        return false;
    }

    // Remove this record from the list of starting applications.
    mPersistentStartingProcesses.remove(app);
    if (DEBUG_PROCESSES && mProcessesOnHold.contains(app)) Slog.v(TAG_PROCESSES,
            "Attach application locked removing on hold: " + app);
    mProcessesOnHold.remove(app);

    boolean badApp = false;
    boolean didSomething = false;

    // See if the top visible activity is waiting to run in this process...
    if (normalMode) {//此处如果已经万事具备就可以将Activity进行绑定到Application中
        try {
            if (mStackSupervisor.attachApplicationLocked(app)) {
                didSomething = true;
            }
        } catch (Exception e) {
            Slog.wtf(TAG, "Exception thrown launching activities in " + app, e);
            badApp = true;
        }
    }

    // Find any services that should be running in this process...
    if (!badApp) {
        try {
            didSomething |= mServices.attachApplicationLocked(app, processName);
            checkTime(startTime, "attachApplicationLocked: after mServices.attachApplicationLocked");
        } catch (Exception e) {
            Slog.wtf(TAG, "Exception thrown starting services in " + app, e);
            badApp = true;
        }
    }

    // Check if a next-broadcast receiver is in this process...
    if (!badApp && isPendingBroadcastProcessLocked(pid)) {
        try {
            didSomething |= sendPendingBroadcastsLocked(app);
            checkTime(startTime, "attachApplicationLocked: after sendPendingBroadcastsLocked");
        } catch (Exception e) {
            // If the app died trying to launch the receiver we declare it 'bad'
            Slog.wtf(TAG, "Exception thrown dispatching broadcasts in " + app, e);
            badApp = true;
        }
    }

    // Check whether the next backup agent is in this process...
    if (!badApp && mBackupTarget != null && mBackupTarget.app == app) {
        if (DEBUG_BACKUP) Slog.v(TAG_BACKUP,
                "New app is backup target, launching agent for " + app);
        notifyPackageUse(mBackupTarget.appInfo.packageName,
                PackageManager.NOTIFY_PACKAGE_USE_BACKUP);
        try {
            thread.scheduleCreateBackupAgent(mBackupTarget.appInfo,
                    compatibilityInfoForPackageLocked(mBackupTarget.appInfo),
                    mBackupTarget.backupMode);
        } catch (Exception e) {
            Slog.wtf(TAG, "Exception thrown creating backup agent in " + app, e);
            badApp = true;
        }
    }

    if (badApp) {
        app.kill("error during init", true);
        handleAppDiedLocked(app, false, true);
        return false;
    }

    if (!didSomething) {
        updateOomAdjLocked();
        checkTime(startTime, "attachApplicationLocked: after updateOomAdjLocked");
    }

    return true;
}

这部分代码有点长，我省略了一部分都是一些数据的检测和一些Application信息的绑定操作。在这里我主要看了两部分，一个是ActivityThread的Application的信息绑定操作，一个是Activity的Application信息绑定操作。接下来直接看Activity的Application的绑定以及启动，看StackSupervisor中attachApplicationLocked方法

2、StackSupervisor的attachApplicationLocked过程

boolean attachApplicationLocked(ProcessRecord app) throws RemoteException {
    final String processName = app.processName;
    boolean didSomething = false;
    for (int displayNdx = mActivityDisplays.size() - 1; displayNdx >= 0; --displayNdx) {
        //获取所有Activity栈
        ArrayList stacks = mActivityDisplays.valueAt(displayNdx).mStacks;
        //获取当前获取焦点Activity栈
        for (int stackNdx = stacks.size() - 1; stackNdx >= 0; --stackNdx) {
            final ActivityStack stack = stacks.get(stackNdx);
            if (!isFocusedStack(stack)) {
                continue;
            }
            //获取当前Activity栈中所有可见的Activity栈
            stack.getAllRunningVisibleActivitiesLocked(mTmpActivityList);
            final ActivityRecord top = stack.topRunningActivityLocked();
            final int size = mTmpActivityList.size();
            //启动当前Activity栈中可见的Activity
            for (int i = 0; i < size; i++) {
                final ActivityRecord activity = mTmpActivityList.get(i);
                if (activity.app == null && app.uid == activity.info.applicationInfo.uid
                        && processName.equals(activity.processName)) {
                    try {//直接看这里了
                        if (realStartActivityLocked(activity, app,
                                top == activity /* andResume */, true /* checkConfig */)) {
                            didSomething = true;
                        }
                    } catch (RemoteException e) {
                        Slog.w(TAG, "Exception in new application when starting activity "
                                + top.intent.getComponent().flattenToShortString(), e);
                        throw e;
                    }
                }
            }
        }
    }
    if (!didSomething) {
        ensureActivitiesVisibleLocked(null, 0, !PRESERVE_WINDOWS);
    }
    return didSomething;
}

在这里会获取到获取焦点的Activity的任务栈，然后获取任务栈中所有的可以显示的Activity，然后启动第一个可以启动的Activity

2、StackSupervisor的realStartActivityLocked过程

final boolean realStartActivityLocked(ActivityRecord r, ProcessRecord app,
                                      boolean andResume, boolean checkConfig) throws RemoteException {

    if (!allPausedActivitiesComplete()) {
        // While there are activities pausing we skipping starting any new activities until
        // pauses are complete. NOTE: that we also do this for activities that are starting in
        // the paused state because they will first be resumed then paused on the client side.
        if (DEBUG_SWITCH || DEBUG_PAUSE || DEBUG_STATES) Slog.v(TAG_PAUSE,
                "realStartActivityLocked: Skipping start of r=" + r
                        + " some activities pausing...");
        return false;
    }

    final TaskRecord task = r.getTask();
    final ActivityStack stack = task.getStack();

    beginDeferResume();

    try {
        r.startFreezingScreenLocked(app, 0);

        // schedule launch ticks to collect information about slow apps.
        r.startLaunchTickingLocked();

        r.app = app;

        if (mKeyguardController.isKeyguardLocked()) {
            r.notifyUnknownVisibilityLaunched();
        }

        // Have the window manager re-evaluate the orientation of the screen based on the new
        // activity order.  Note that as a result of this, it can call back into the activity
        // manager with a new orientation.  We don't care about that, because the activity is
        // not currently running so we are just restarting it anyway.
        if (checkConfig) {
            final int displayId = r.getDisplayId();
            final Configuration config = mWindowManager.updateOrientationFromAppTokens(
                    getDisplayOverrideConfiguration(displayId),
                    r.mayFreezeScreenLocked(app) ? r.appToken : null, displayId);
            // Deferring resume here because we're going to launch new activity shortly.
            // We don't want to perform a redundant launch of the same record while ensuring
            // configurations and trying to resume top activity of focused stack.
            mService.updateDisplayOverrideConfigurationLocked(config, r, true /* deferResume */,
                    displayId);
        }

        if (r.getStack().checkKeyguardVisibility(r, true /* shouldBeVisible */,
                true /* isTop */)) {
            // We only set the visibility to true if the activity is allowed to be visible
            // based on
            // keyguard state. This avoids setting this into motion in window manager that is
            // later cancelled due to later calls to ensure visible activities that set
            // visibility back to false.
            r.setVisibility(true);
        }

        final int applicationInfoUid =
                (r.info.applicationInfo != null) ? r.info.applicationInfo.uid : -1;
        if ((r.userId != app.userId) || (r.appInfo.uid != applicationInfoUid)) {
            Slog.wtf(TAG,
                    "User ID for activity changing for " + r
                            + " appInfo.uid=" + r.appInfo.uid
                            + " info.ai.uid=" + applicationInfoUid
                            + " old=" + r.app + " new=" + app);
        }

        app.waitingToKill = null;
        r.launchCount++;
        r.lastLaunchTime = SystemClock.uptimeMillis();

        if (DEBUG_ALL) Slog.v(TAG, "Launching: " + r);

        int idx = app.activities.indexOf(r);
        if (idx < 0) {
            app.activities.add(r);
        }
        //更新进程的使用情况，当内存紧张时，将按照进程的种类及使用情况kill一些进程。
        mService.updateLruProcessLocked(app, true, null);
        //完成进程的oom_adj更新
        mService.updateOomAdjLocked();

        if (task.mLockTaskAuth == LOCK_TASK_AUTH_LAUNCHABLE ||
                task.mLockTaskAuth == LOCK_TASK_AUTH_LAUNCHABLE_PRIV) {
            setLockTaskModeLocked(task, LOCK_TASK_MODE_LOCKED, "mLockTaskAuth==LAUNCHABLE",
                    false);
        }

        try {
            if (app.thread == null) {
                throw new RemoteException();
            }
            List results = null;
            List newIntents = null;
            if (andResume) {
                // We don't need to deliver new intents and/or set results if activity is going
                // to pause immediately after launch.
                results = r.results;
                newIntents = r.newIntents;
            }
            if (DEBUG_SWITCH) Slog.v(TAG_SWITCH,
                    "Launching: " + r + " icicle=" + r.icicle + " with results=" + results
                            + " newIntents=" + newIntents + " andResume=" + andResume);
            EventLog.writeEvent(EventLogTags.AM_RESTART_ACTIVITY, r.userId,
                    System.identityHashCode(r), task.taskId, r.shortComponentName);
            if (r.isHomeActivity()) {
                // Home process is the root process of the task.
                mService.mHomeProcess = task.mActivities.get(0).app;
            }
            mService.notifyPackageUse(r.intent.getComponent().getPackageName(),
                    PackageManager.NOTIFY_PACKAGE_USE_ACTIVITY);
            r.sleeping = false;
            r.forceNewConfig = false;
            mService.showUnsupportedZoomDialogIfNeededLocked(r);
            mService.showAskCompatModeDialogLocked(r);
            r.compat = mService.compatibilityInfoForPackageLocked(r.info.applicationInfo);
            ProfilerInfo profilerInfo = null;
            if (mService.mProfileApp != null && mService.mProfileApp.equals(app.processName)) {
                if (mService.mProfileProc == null || mService.mProfileProc == app) {
                    mService.mProfileProc = app;
                    ProfilerInfo profilerInfoSvc = mService.mProfilerInfo;
                    if (profilerInfoSvc != null && profilerInfoSvc.profileFile != null) {
                        if (profilerInfoSvc.profileFd != null) {
                            try {
                                profilerInfoSvc.profileFd = profilerInfoSvc.profileFd.dup();
                            } catch (IOException e) {
                                profilerInfoSvc.closeFd();
                            }
                        }

                        profilerInfo = new ProfilerInfo(profilerInfoSvc);
                    }
                }
            }

            app.hasShownUi = true;
            app.pendingUiClean = true;
            app.forceProcessStateUpTo(mService.mTopProcessState);
            // Because we could be starting an Activity in the system process this may not go
            // across a Binder interface which would create a new Configuration. Consequently
            // we have to always create a new Configuration here.

            final MergedConfiguration mergedConfiguration = new MergedConfiguration(
                    mService.getGlobalConfiguration(), r.getMergedOverrideConfiguration());
            r.setLastReportedConfiguration(mergedConfiguration);

            logIfTransactionTooLarge(r.intent, r.icicle);
            //此处调用ActivityThread中的ApplicationThread中方法来显示Activity
            app.thread.scheduleLaunchActivity(new Intent(r.intent), r.appToken,
                    System.identityHashCode(r), r.info,
                    // TODO: Have this take the merged configuration instead of separate global
                    // and override configs.
                    mergedConfiguration.getGlobalConfiguration(),
                    mergedConfiguration.getOverrideConfiguration(), r.compat,
                    r.launchedFromPackage, task.voiceInteractor, app.repProcState, r.icicle,
                    r.persistentState, results, newIntents, !andResume,
                    mService.isNextTransitionForward(), profilerInfo);

            if ((app.info.privateFlags & ApplicationInfo.PRIVATE_FLAG_CANT_SAVE_STATE) != 0) {
                // This may be a heavy-weight process!  Note that the package
                // manager will ensure that only activity can run in the main
                // process of the .apk, which is the only thing that will be
                // considered heavy-weight.
                if (app.processName.equals(app.info.packageName)) {
                    if (mService.mHeavyWeightProcess != null
                            && mService.mHeavyWeightProcess != app) {
                        Slog.w(TAG, "Starting new heavy weight process " + app
                                + " when already running "
                                + mService.mHeavyWeightProcess);
                    }
                    mService.mHeavyWeightProcess = app;
                    Message msg = mService.mHandler.obtainMessage(
                            ActivityManagerService.POST_HEAVY_NOTIFICATION_MSG);
                    msg.obj = r;
                    mService.mHandler.sendMessage(msg);
                }
            }

        } catch (RemoteException e) {
            if (r.launchFailed) {
                // This is the second time we failed -- finish activity
                // and give up.
                Slog.e(TAG, "Second failure launching "
                        + r.intent.getComponent().flattenToShortString()
                        + ", giving up", e);
                mService.appDiedLocked(app);
                stack.requestFinishActivityLocked(r.appToken, Activity.RESULT_CANCELED, null,
                        "2nd-crash", false);
                return false;
            }

            // This is the first time we failed -- restart process and
            // retry.
            r.launchFailed = true;
            app.activities.remove(r);
            throw e;
        }
    } finally {
        endDeferResume();
    }

    r.launchFailed = false;
    if (stack.updateLRUListLocked(r)) {
        Slog.w(TAG, "Activity " + r + " being launched, but already in LRU list");
    }

    if (andResume && readyToResume()) {
        // As part of the process of launching, ActivityThread also performs
        // a resume.
        stack.minimalResumeActivityLocked(r);
    } else {
        // This activity is not starting in the resumed state... which should look like we asked
        // it to pause+stop (but remain visible), and it has done so and reported back the
        // current icicle and other state.
        if (DEBUG_STATES) Slog.v(TAG_STATES,
                "Moving to PAUSED: " + r + " (starting in paused state)");
        r.state = PAUSED;
    }

    // Launch the new version setup screen if needed.  We do this -after-
    // launching the initial activity (that is, home), so that it can have
    // a chance to initialize itself while in the background, making the
    // switch back to it faster and look better.
    if (isFocusedStack(stack)) {
        mService.startSetupActivityLocked();
    }

    // Update any services we are bound to that might care about whether
    // their client may have activities.
    if (r.app != null) {
        mService.mServices.updateServiceConnectionActivitiesLocked(r.app);
    }

    return true;
}

在这里首先是更新了AMS中的进程，然后更新oom_adj的值，最后调用ActivityThread中的ApplicationThread中方法启动Activity。

三 ApplicationThread启动Activity

1 scheduleLaunchActivity过程

public final void scheduleLaunchActivity(Intent intent, IBinder token, int ident,
                                         ActivityInfo info, Configuration curConfig, CompatibilityInfo compatInfo,
                                         Bundle state, List pendingResults,
                                         List pendingNewIntents, boolean notResumed, boolean isForward,
                                         String profileName, ParcelFileDescriptor profileFd, boolean autoStopProfiler) {
    ActivityClientRecord r = new ActivityClientRecord()

    r.token = token;
    r.ident = ident;
    r.intent = intent;
    r.activityInfo = info;
    r.compatInfo = compatInfo;
    r.state = state;

    r.pendingResults = pendingResults;
    r.pendingIntents = pendingNewIntents;

    r.startsNotResumed = notResumed;
    r.isForward = isForward;

    r.profileFile = profileName;
    r.profileFd = profileFd;
    r.autoStopProfiler = autoStopProfiler;

    updatePendingConfiguration(curConfig);
    //发送LAUNCH_ACTIVITY类型消息
    queueOrSendMessage(H.LAUNCH_ACTIVITY, r);
}

这里的操作相当简单，就是变量的赋值然后发送一个消息。下面直接看消息

2 handler消息处理过程

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");
            ActivityClientRecord r = (ActivityClientRecord) msg.obj;

            r.packageInfo = getPackageInfoNoCheck(
                    r.activityInfo.applicationInfo, r.compatInfo);
            handleLaunchActivity(r, null);
            Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
        }
        break;
    }
}

这里也是比较简单的处理过程，最后交给handleLaunchActivity处理Activity的启动

3 handleLaunchActivity处理过程

private void handleLaunchActivity(ActivityClientRecord r, Intent customIntent) {
    // If we are getting ready to gc after going to the background, well
    // we are back active so skip it.
    unscheduleGcIdler();

    if (r.profileFd != null) {
        mProfiler.setProfiler(r.profileFile, r.profileFd);
        mProfiler.startProfiling();
        mProfiler.autoStopProfiler = r.autoStopProfiler;
    }

    // Make sure we are running with the most recent config.
    handleConfigurationChanged(null, null);

    if (localLOGV) Slog.v(
            TAG, "Handling launch of " + r);
    //启动Activity
    Activity a = performLaunchActivity(r, customIntent);

    if (a != null) { //前面启动成功，这里
        r.createdConfig = new Configuration(mConfiguration);
        Bundle oldState = r.state;
        handleResumeActivity(r.token, false, r.isForward,
                !r.activity.mFinished && !r.startsNotResumed);

        if (!r.activity.mFinished && r.startsNotResumed) {
            // The activity manager actually wants this one to start out
            // paused, because it needs to be visible but isn't in the
            // foreground.  We accomplish this by going through the
            // normal startup (because activities expect to go through
            // onResume() the first time they run, before their window
            // is displayed), and then pausing it.  However, in this case
            // we do -not- need to do the full pause cycle (of freezing
            // and such) because the activity manager assumes it can just
            // retain the current state it has.
            try {
                r.activity.mCalled = false;
                mInstrumentation.callActivityOnPause(r.activity);
                // We need to keep around the original state, in case
                // we need to be created again.  But we only do this
                // for pre-Honeycomb apps, which always save their state
                // when pausing, so we can not have them save their state
                // when restarting from a paused state.  For HC and later,
                // we want to (and can) let the state be saved as the normal
                // part of stopping the activity.
                if (r.isPreHoneycomb()) {
                    r.state = oldState;
                }
                if (!r.activity.mCalled) {
                    throw new SuperNotCalledException(
                            "Activity " + r.intent.getComponent().toShortString() +
                                    " did not call through to super.onPause()");
                }

            } catch (SuperNotCalledException e) {
                throw e;

            } catch (Exception e) {
                if (!mInstrumentation.onException(r.activity, e)) {
                    throw new RuntimeException(
                            "Unable to pause activity "
                                    + r.intent.getComponent().toShortString()
                                    + ": " + e.toString(), e);
                }
            }
            r.paused = true;
        }
    } else {
        // If there was an error, for any reason, tell the activity
        // manager to stop us.
        try {
            ActivityManagerNative.getDefault()
                    .finishActivity(r.token, Activity.RESULT_CANCELED, null);
        } catch (RemoteException ex) {
            // Ignore
        }
    }
}

这里两个地方，一个是performLaunchActivity启动Activity，一个就是handleResumeActivity启动Activity。接下来看一下performLaunchActivity这个方法

4 performLaunchActivity过程

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();
        //创建Activity实例
        activity = mInstrumentation.newActivity(
                cl, component.getClassName(), r.intent);
        StrictMode.incrementExpectedActivityCount(activity.getClass());
        r.intent.setExtrasClassLoader(cl);
        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 {
        //设置Application
        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) {
            //生成Context
            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);
            //绑定Activity、Application、Context
            activity.attach(appContext, this, getInstrumentation(), r.token,
                    r.ident, app, r.intent, r.activityInfo, title, r.parent,
                    r.embeddedID, r.lastNonConfigurationInstances, config);

            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;
            //调用Activity的OnCreate方法
            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;
            //调用Activity的start方法
            if (!r.activity.mFinished) {
                activity.performStart();
                r.stopped = false;
            }
            if (!r.activity.mFinished) {
                if (r.state != null) {
                    mInstrumentation.callActivityOnRestoreInstanceState(activity, r.state);
                }
            }
            if (!r.activity.mFinished) {
                activity.mCalled = false;
                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;
}

到这里差不多讲完了，在这里创建Activity的实例之后进行绑定操作。然后可以看到Activity的的生命周期的方法。

总结

关于ActivityThread中如何启动Activity讲解完成，过程相对来说比较简单。不过，整个过程中没有仔细看其他的过程，比如AMS中的进程刷新，oom_adj值的刷新都没有讲解，其中涉及到的东西有点多以后有机会另外写两篇文章讲解一下。

这里也不能说完全简介完Activity的启动的过程，关于绑定过程中会涉及到的过程没有讲解。