startService分析（1）

1.来源于百度图片

从上面可以知道Service是继承于ContextWrapper,而ContextWrapper和ContextImpl继承Context抽象类，但Context中的方法实现是在ContextImpl中实现。

我们在Activity中调startService()方法是ContextWrapper中的

ContextWrapper.java

    @Override
    public ComponentName startService(Intent service) {
        return mBase.startService(service); 此中的mBase就是Context，但Context中的方法具体实现是在ContextImpl中
    }

ContextImpl.java

在ContextImpl.java中有如下注释

/**
 * Common implementation of Context API, which provides the base
 * context object for Activity and other application components.
 */

我们继续

    @Override
    public ComponentName startService(Intent service) {
        warnIfCallingFromSystemProcess();这个只是警告，如果不是Process.SYSTEM_UID
        return startServiceCommon(service, mUser);1.0 startServiceCommon
    }

1.0 startServiceCommon()

    private ComponentName startServiceCommon(Intent service, UserHandle user) {
        try {
            validateServiceIntent(service);检查Service是否有效
            service.prepareToLeaveProcess();
            ActivityManagerNative.getDefault()其实就是ActivityManagerProxy对象，然后调用ActivityManagerProxy中的StartService（）
            我们详细分析【2.0 ActivityManagerNative.getDefault()  3.0 ActivityManagerProxy.startService()
            ComponentName cn = ActivityManagerNative.getDefault().startService(
                mMainThread.getApplicationThread(), service, service.resolveTypeIfNeeded(
                            getContentResolver()), getOpPackageName(), user.getIdentifier());
            if (cn != null) {
                if (cn.getPackageName().equals("!")) {
                    throw new SecurityException(
                            "Not allowed to start service " + service
                            + " without permission " + cn.getClassName());
                } else if (cn.getPackageName().equals("!!")) {
                    throw new SecurityException(
                            "Unable to start service " + service
                            + ": " + cn.getClassName());
                }
            }
            return cn;
        } catch (RemoteException e) {
            throw new RuntimeException("Failure from system", e);
        }
    }

2.0 ActivityManagerNative.getDefault()

    /**
     * Retrieve the system's default/global activity manager.
     */
    static public IActivityManager getDefault() {
        return gDefault.get(); 这个get()方法其实就是调用了IActivityManager的create()方法，，先看Singleton中的代码
    }

    private static final Singleton<IActivityManager> gDefault = new Singleton<IActivityManager>() {
        protected IActivityManager create() {
            IBinder b = ServiceManager.getService("activity");
            if (false) {
                Log.v("ActivityManager", "default service binder = " + b);
            }
            IActivityManager am = asInterface(b);
            if (false) {
                Log.v("ActivityManager", "default service = " + am);
            }
            return am;
        }
    };


public abstract class Singleton<T> {
    private T mInstance;

    protected abstract T create();

    public final T get() {
        synchronized (this) {
            if (mInstance == null) {
                mInstance = create();
            }
            return mInstance;
        }
    }
}


    /**
     * Cast a Binder object into an activity manager interface, generating
     * a proxy if needed.
     */
    static public IActivityManager asInterface(IBinder obj) {
        if (obj == null) {
            return null;
        }
        第一次没有初始化，是null
        IActivityManager in =
            (IActivityManager)obj.queryLocalInterface(descriptor);
        if (in != null) {
            return in;
        }
         第一次走这里
        return new ActivityManagerProxy(obj);
    }

所以说ActivityManagerNative.getDefault().startService()就是等于ActivityManagerProxy.startService()

3.0 ActivityManagerProxy.startService()方法

    public ComponentName startService(IApplicationThread caller, Intent service,
            String resolvedType, String callingPackage, int userId) throws RemoteException
    {
        Parcel data = Parcel.obtain();
        Parcel reply = Parcel.obtain();
        data.writeInterfaceToken(IActivityManager.descriptor);
        data.writeStrongBinder(caller != null ? caller.asBinder() : null);
        service.writeToParcel(data, 0);
        data.writeString(resolvedType);
        data.writeString(callingPackage);
        data.writeInt(userId);
        mRemote就是一个IBinder，这里通过Binder进行了跨进程通信，最后会运行到ActivityManagerNative.onTransact()中
        mRemote.transact(START_SERVICE_TRANSACTION, data, reply, 0);
        reply.readException();
        ComponentName res = ComponentName.readFromParcel(reply);
        data.recycle();
        reply.recycle();
        return res;
    }

到这了，我们不得不提ActivityManagerProxy和ActivityManagerNative之间的关系两者都实现IActivityManager接口，且ActivityManagerNative继承Binder

这里使用了Binder机制进行跨进程通信（下图只是展示大概的意思）

2.来源百度图片

ActivityManagerProxy看做是客户端，ActivityManagerNative看作是服务端（图2并没有展示出来）。由于暂时对Binder机制不是很了解，这里暂时跳过。

4.0 ActivityManagerNative.onTransact()

@Override
    public boolean onTransact(int code, Parcel data, Parcel reply, int flags)
            throws RemoteException {
        ......
        case START_SERVICE_TRANSACTION: {
            data.enforceInterface(IActivityManager.descriptor);
            IBinder b = data.readStrongBinder();
            IApplicationThread app = ApplicationThreadNative.asInterface(b);
            Intent service = Intent.CREATOR.createFromParcel(data);
            String resolvedType = data.readString();
            String callingPackage = data.readString();
            int userId = data.readInt();
            ActivityManagerNative是个抽象类，并没有实现startService()方法，但是其继承者ActivityManagerService实现了StartService()
            5.0 ActivityManagerService.startService()
            ComponentName cn = startService(app, service, resolvedType, callingPackage, userId);
            reply.writeNoException();
            ComponentName.writeToParcel(cn, reply);
            return true;
        }
        .......
}

5.0 ActivityManagerService.startService()

    @Override
    public ComponentName startService(IApplicationThread caller, Intent service,
            String resolvedType, String callingPackage, int userId)
            throws TransactionTooLargeException {
        enforceNotIsolatedCaller("startService");
        // Refuse possible leaked file descriptors
        if (service != null && service.hasFileDescriptors() == true) {
            throw new IllegalArgumentException("File descriptors passed in Intent");
        }

        if (callingPackage == null) {
            throw new IllegalArgumentException("callingPackage cannot be null");
        }

        if (DEBUG_SERVICE) Slog.v(TAG_SERVICE,
                "startService: " + service + " type=" + resolvedType);
        synchronized(this) {
            final int callingPid = Binder.getCallingPid();
            final int callingUid = Binder.getCallingUid();
            final long origId = Binder.clearCallingIdentity();
            6.0 mServices.startServiceLocked
            ComponentName res = mServices.startServiceLocked(caller, service, //此处的mService是ActiveServices
                    resolvedType, callingPid, callingUid, callingPackage, userId);
            Binder.restoreCallingIdentity(origId);
            return res;
        }
    }

6.0ActiveServices.startServiceLocked

    ComponentName startServiceLocked(IApplicationThread caller, Intent service, String resolvedType,
            int callingPid, int callingUid, String callingPackage, int userId)
            throws TransactionTooLargeException {
        if (DEBUG_DELAYED_STARTS) Slog.v(TAG_SERVICE, "startService: " + service
                + " type=" + resolvedType + " args=" + service.getExtras());

        final boolean callerFg;
        if (caller != null) {
            final ProcessRecord callerApp = mAm.getRecordForAppLocked(caller);
            if (callerApp == null) {
                throw new SecurityException(
                        "Unable to find app for caller " + caller
                        + " (pid=" + Binder.getCallingPid()
                        + ") when starting service " + service);
            }
            callerFg = callerApp.setSchedGroup != Process.THREAD_GROUP_BG_NONINTERACTIVE;
        } else {
            callerFg = true;
        }

        检索服务信息
        ServiceLookupResult res =
            retrieveServiceLocked(service, resolvedType, callingPackage,
                    callingPid, callingUid, userId, true, callerFg);
        if (res == null) {
            return null;
        }
        if (res.record == null) {
            return new ComponentName("!", res.permission != null
                    ? res.permission : "private to package");
        }

        ServiceRecord r = res.record;
        检查是否存在启动此Service的User
        if (!mAm.getUserManagerLocked().exists(r.userId)) {
            Slog.d(TAG, "Trying to start service with non-existent user! " + r.userId);
            return null;
        }
        //
        NeededUriGrants neededGrants = mAm.checkGrantUriPermissionFromIntentLocked(
                callingUid, r.packageName, service, service.getFlags(), null, r.userId);
        if (unscheduleServiceRestartLocked(r, callingUid, false)) {
            if (DEBUG_SERVICE) Slog.v(TAG_SERVICE, "START SERVICE WHILE RESTART PENDING: " + r);
        }
        r.lastActivity = SystemClock.uptimeMillis();
        r.startRequested = true;
        r.delayedStop = false;
        r.pendingStarts.add(new ServiceRecord.StartItem(r, false, r.makeNextStartId(),
                service, neededGrants));

        final ServiceMap smap = getServiceMap(r.userId);
        boolean addToStarting = false;
        下面直接看英文注释啦，，，我英文差，，懒得Google翻译出来
        if (!callerFg && r.app == null && mAm.mStartedUsers.get(r.userId) != null) {
            ProcessRecord proc = mAm.getProcessRecordLocked(r.processName, r.appInfo.uid, false);
            if (proc == null || proc.curProcState > ActivityManager.PROCESS_STATE_RECEIVER) {
                // If this is not coming from a foreground caller, then we may want
                // to delay the start if there are already other background services
                // that are starting.  This is to avoid process start spam when lots
                // of applications are all handling things like connectivity broadcasts.
                // We only do this for cached processes, because otherwise an application
                // can have assumptions about calling startService() for a service to run
                // in its own process, and for that process to not be killed before the
                // service is started.  This is especially the case for receivers, which
                // may start a service in onReceive() to do some additional work and have
                // initialized some global state as part of that.
                if (DEBUG_DELAYED_SERVICE) Slog.v(TAG_SERVICE, "Potential start delay of "
                        + r + " in " + proc);
                if (r.delayed) {
                    // This service is already scheduled for a delayed start; just leave
                    // it still waiting.
                    if (DEBUG_DELAYED_STARTS) Slog.v(TAG_SERVICE, "Continuing to delay: " + r);
                    return r.name;
                }
                if (smap.mStartingBackground.size() >= mMaxStartingBackground) {
                    // Something else is starting, delay!
                    Slog.i(TAG_SERVICE, "Delaying start of: " + r);
                    smap.mDelayedStartList.add(r);
                    r.delayed = true;
                    return r.name;
                }
                if (DEBUG_DELAYED_STARTS) Slog.v(TAG_SERVICE, "Not delaying: " + r);
                addToStarting = true;
            } else if (proc.curProcState >= ActivityManager.PROCESS_STATE_SERVICE) {
                // We slightly loosen when we will enqueue this new service as a background
                // starting service we are waiting for, to also include processes that are
                // currently running other services or receivers.
                addToStarting = true;
                if (DEBUG_DELAYED_STARTS) Slog.v(TAG_SERVICE,
                        "Not delaying, but counting as bg: " + r);
            } else if (DEBUG_DELAYED_STARTS) {
                StringBuilder sb = new StringBuilder(128);
                sb.append("Not potential delay (state=").append(proc.curProcState)
                        .append(' ').append(proc.adjType);
                String reason = proc.makeAdjReason();
                if (reason != null) {
                    sb.append(' ');
                    sb.append(reason);
                }
                sb.append("): ");
                sb.append(r.toString());
                Slog.v(TAG_SERVICE, sb.toString());
            }
        } else if (DEBUG_DELAYED_STARTS) {
            if (callerFg) {
                Slog.v(TAG_SERVICE, "Not potential delay (callerFg=" + callerFg + " uid="
                        + callingUid + " pid=" + callingPid + "): " + r);
            } else if (r.app != null) {
                Slog.v(TAG_SERVICE, "Not potential delay (cur app=" + r.app + "): " + r);
            } else {
                Slog.v(TAG_SERVICE,
                        "Not potential delay (user " + r.userId + " not started): " + r);
            }
        }
         7.0 startServiceInnerLocked
        return startServiceInnerLocked(smap, service, r, callerFg, addToStarting);
    }

7.0 ActiveServices.startServiceInnerLocked()

    ComponentName startServiceInnerLocked(ServiceMap smap, Intent service, ServiceRecord r,
            boolean callerFg, boolean addToStarting) throws TransactionTooLargeException {
        ProcessStats.ServiceState stracker = r.getTracker();
        if (stracker != null) {
            stracker.setStarted(true, mAm.mProcessStats.getMemFactorLocked(), r.lastActivity);
        }
        r.callStart = false;
        synchronized (r.stats.getBatteryStats()) {
            r.stats.startRunningLocked();
        }
        8.0 bringUpServiceLocked
        String error = bringUpServiceLocked(r, service.getFlags(), callerFg, false);
        if (error != null) {
            return new ComponentName("!!", error);
        }

        if (r.startRequested && addToStarting) {
            boolean first = smap.mStartingBackground.size() == 0;
            smap.mStartingBackground.add(r);
            r.startingBgTimeout = SystemClock.uptimeMillis() + BG_START_TIMEOUT;
            if (DEBUG_DELAYED_SERVICE) {
                RuntimeException here = new RuntimeException("here");
                here.fillInStackTrace();
                Slog.v(TAG_SERVICE, "Starting background (first=" + first + "): " + r, here);
            } else if (DEBUG_DELAYED_STARTS) {
                Slog.v(TAG_SERVICE, "Starting background (first=" + first + "): " + r);
            }
            if (first) {
                smap.rescheduleDelayedStarts();
            }
        } else if (callerFg) {
            smap.ensureNotStartingBackground(r);
        }

        return r.name;
    }

8.0 ActiveServices.bringUpServiceLocked()

直接看英文吧，都写得很清楚

    private final String bringUpServiceLocked(ServiceRecord r, int intentFlags, boolean execInFg,
            boolean whileRestarting) throws TransactionTooLargeException {
        //Slog.i(TAG, "Bring up service:");
        //r.dump("  ");

        if (r.app != null && r.app.thread != null) {
            sendServiceArgsLocked(r, execInFg, false);
            return null;
        }

        if (!whileRestarting && r.restartDelay > 0) {
            // If waiting for a restart, then do nothing.
            return null;
        }

        if (DEBUG_SERVICE) Slog.v(TAG_SERVICE, "Bringing up " + r + " " + r.intent);

        // We are now bringing the service up, so no longer in the
        // restarting state.
        if (mRestartingServices.remove(r)) {
            r.resetRestartCounter();
            clearRestartingIfNeededLocked(r);
        }

        // Make sure this service is no longer considered delayed, we are starting it now.
        if (r.delayed) {
            if (DEBUG_DELAYED_STARTS) Slog.v(TAG_SERVICE, "REM FR DELAY LIST (bring up): " + r);
            getServiceMap(r.userId).mDelayedStartList.remove(r);
            r.delayed = false;
        }

        // Make sure that the user who owns this service is started.  If not,
        // we don't want to allow it to run.
        if (mAm.mStartedUsers.get(r.userId) == null) {检查User的状态，如果user不存在就关闭服务
            String msg = "Unable to launch app "
                    + r.appInfo.packageName + "/"
                    + r.appInfo.uid + " for service "
                    + r.intent.getIntent() + ": user " + r.userId + " is stopped";
            Slog.w(TAG, msg);
            bringDownServiceLocked(r);
            return msg;
        }

        // Service is now being launched, its package can't be stopped.
        try {
            AppGlobals.getPackageManager().setPackageStoppedState(
                    r.packageName, false, r.userId);
        } catch (RemoteException e) {
        } catch (IllegalArgumentException e) {
            Slog.w(TAG, "Failed trying to unstop package "
                    + r.packageName + ": " + e);
        }

        final boolean isolated = (r.serviceInfo.flags&ServiceInfo.FLAG_ISOLATED_PROCESS) != 0;
        final String procName = r.processName;
        ProcessRecord app;
        这里是判读是否是独立进程，如果不是就可以直接启动服务，如果是需要启动进程
        if (!isolated) {
            获取进程
            app = mAm.getProcessRecordLocked(procName, r.appInfo.uid, false);
            if (DEBUG_MU) Slog.v(TAG_MU, "bringUpServiceLocked: appInfo.uid=" + r.appInfo.uid
                        + " app=" + app);
            if (app != null && app.thread != null) {
                try {
                    添加相应的包名
                    app.addPackage(r.appInfo.packageName, r.appInfo.versionCode, mAm.mProcessStats);
                    9.0 realStartServiceLocked真正启动服务
                    realStartServiceLocked(r, app, execInFg);
                    return null;
                } catch (TransactionTooLargeException e) {
                    throw e;
                } catch (RemoteException e) {
                    Slog.w(TAG, "Exception when starting service " + r.shortName, e);
                }

                // If a dead object exception was thrown -- fall through to
                // restart the application.
            }
        } else {
            // If this service runs in an isolated process, then each time
            // we call startProcessLocked() we will get a new isolated
            // process, starting another process if we are currently waiting
            // for a previous process to come up.  To deal with this, we store
            // in the service any current isolated process it is running in or
            // waiting to have come up.
            app = r.isolatedProc;
        }

        // Not running -- get it started, and enqueue this service record
        // to be executed when the app comes up.
        if (app == null) {
            10. startProcessLocked启动对应的进程
            if ((app=mAm.startProcessLocked(procName, r.appInfo, true, intentFlags,
                    "service", r.name, false, isolated, false)) == null) {
                如果启动进程失败，，，
                String msg = "Unable to launch app "
                        + r.appInfo.packageName + "/"
                        + r.appInfo.uid + " for service "
                        + r.intent.getIntent() + ": process is bad";
                Slog.w(TAG, msg);
                bringDownServiceLocked(r);
                return msg;
            }
            if (isolated) {
                r.isolatedProc = app;
            }
        }

        if (!mPendingServices.contains(r)) {
            mPendingServices.add(r);
        }

        if (r.delayedStop) {
            // Oh and hey we've already been asked to stop!
            r.delayedStop = false;
            if (r.startRequested) {
                if (DEBUG_DELAYED_STARTS) Slog.v(TAG_SERVICE,
                        "Applying delayed stop (in bring up): " + r);
                stopServiceLocked(r);
            }
        }

        return null;
    }

9.0 片段代码分支 我们后面再跟进[-----请看10.8分析-----]

10. startProcessLocked启动对应的进程

    private final void startProcessLocked(ProcessRecord app,
            String hostingType, String hostingNameStr) {
        startProcessLocked(app, hostingType, hostingNameStr, null /* abiOverride */,
                null /* entryPoint */, null /* entryPointArgs */);
    }


    private final void startProcessLocked(ProcessRecord app, String hostingType,
            String hostingNameStr, String abiOverride, String entryPoint, String[] entryPointArgs) {
           .......
            app.gids = gids;
            app.requiredAbi = requiredAbi;
            app.instructionSet = instructionSet;

            // Start the process.  It will either succeed and return a result containing
            // the PID of the new process, or else throw a RuntimeException.
           添加android.app.ActivityThread
            boolean isActivityProcess = (entryPoint == null);
            if (entryPoint == null) entryPoint = "android.app.ActivityThread";
            Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "Start proc: " +
                    app.processName);
            checkTime(startTime, "startProcess: asking zygote to start proc");
           10.1 启动Process.start ()来启动android.app.ActivityThread 
            Process.ProcessStartResult startResult = Process.start(entryPoint,
                    app.processName, uid, uid, gids, debugFlags, mountExternal,
                    app.info.targetSdkVersion, app.info.seinfo, requiredAbi, instructionSet,
                    app.info.dataDir, entryPointArgs);
            checkTime(startTime, "startProcess: returned from zygote!");
            Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);

            if (app.isolated) {
                mBatteryStatsService.addIsolatedUid(app.uid, app.info.uid);
            }
          .......
    }

10.1 启动Process.start ()来启动android.app.ActivityThread

    public static final ProcessStartResult start(final String processClass,
                                  final String niceName,
                                  int uid, int gid, int[] gids,
                                  int debugFlags, int mountExternal,
                                  int targetSdkVersion,
                                  String seInfo,
                                  String abi,
                                  String instructionSet,
                                  String appDataDir,
                                  String[] zygoteArgs) {
        try {
            return startViaZygote(processClass, niceName, uid, gid, gids,
                    debugFlags, mountExternal, targetSdkVersion, seInfo,
                    abi, instructionSet, appDataDir, zygoteArgs);
        } catch (ZygoteStartFailedEx ex) {
            Log.e(LOG_TAG,
                    "Starting VM process through Zygote failed");
            throw new RuntimeException(
                    "Starting VM process through Zygote failed", ex);
        }
    }

上面就使用startViaZygote等一步一步的请我们传入的参数“android.app.ActivityThread”，并启动它

启动过程我们暂时忽略，直接进入ActivityThread的main()方法。

10.2 ActivityThread.main()

    public static void main(String[] args) {
        Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "ActivityThreadMain");
        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());

        AndroidKeyStoreProvider.install();

        // Make sure TrustedCertificateStore looks in the right place for CA certificates
        final File configDir = Environment.getUserConfigDirectory(UserHandle.myUserId());
        TrustedCertificateStore.setDefaultUserDirectory(configDir);

        Process.setArgV0("<pre-initialized>");

        Looper.prepareMainLooper(); 初始化UI线程的Looper

        创建ActivityThread,这里是ResourceManager的初始化
        ActivityThread thread = new ActivityThread();
        10.3 ActivityThread.attach()
        thread.attach(false);

        if (sMainThreadHandler == null) {
            sMainThreadHandler = thread.getHandler();
        }

        if (false) {
            Looper.myLooper().setMessageLogging(new
                    LogPrinter(Log.DEBUG, "ActivityThread"));
        }

        // End of event ActivityThreadMain.
        Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
        Looper.loop(); 开启Looper循环，，很熟悉吧

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

10.3 ActivityThread.attach()

    private void attach(boolean system) {
        sCurrentActivityThread = this;
        mSystemThread = system; //false
        if (!system) {
            ViewRootImpl.addFirstDrawHandler(new Runnable() {
                @Override
                public void run() {
                    ensureJitEnabled();
                }
            });
            android.ddm.DdmHandleAppName.setAppName("<pre-initialized>",
                                                    UserHandle.myUserId());
            RuntimeInit.setApplicationObject(mAppThread.asBinder());
            获取的又是ActivityManagerProxy对象
            final IActivityManager mgr = ActivityManagerNative.getDefault();
            try {
                mgr.attachApplication(mAppThread); 10.4 ActivityManagerProxy.attachApplication，但最终还是跑到了ActivityManagerService中attachApplication中
            } catch (RemoteException ex) {
                // Ignore
            }
            // Watch for getting close to heap limit.
            BinderInternal.addGcWatcher(new Runnable() {
                @Override public void run() {
                    if (!mSomeActivitiesChanged) {
                        return;
                    }
                    Runtime runtime = Runtime.getRuntime();
                    long dalvikMax = runtime.maxMemory();
                    long dalvikUsed = runtime.totalMemory() - runtime.freeMemory();
                    if (dalvikUsed > ((3*dalvikMax)/4)) {
                        if (DEBUG_MEMORY_TRIM) Slog.d(TAG, "Dalvik max=" + (dalvikMax/1024)
                                + " total=" + (runtime.totalMemory()/1024)
                                + " used=" + (dalvikUsed/1024));
                        mSomeActivitiesChanged = false;
                        try {
                            mgr.releaseSomeActivities(mAppThread);
                        } catch (RemoteException e) {
                        }
                    }
                }
            });
        } 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 = ContextImpl.createAppContext(
                        this, getSystemContext().mPackageInfo);
                这里就是开始启动Application了，所以每个应用第一启动的就是Application中的代码
                mInitialApplication = context.mPackageInfo.makeApplication(true, null);
                mInitialApplication.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() {
            @Override
            public void onConfigurationChanged(Configuration newConfig) {
                synchronized (mResourcesManager) {
                    // We need to apply this change to the resources
                    // immediately, because upon returning the view
                    // hierarchy will be informed about it.
                     mResourcesManager的初始化是在ActivityThread()中
                    if (mResourcesManager.applyConfigurationToResourcesLocked(newConfig, null)) {
                        // This actually changed the resources!  Tell
                        // everyone about it.
                        if (mPendingConfiguration == null ||
                                mPendingConfiguration.isOtherSeqNewer(newConfig)) {
                            mPendingConfiguration = newConfig;

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

由于篇幅太长了，因此分开，后续文章继续讲解。