ActivityManagerService:從startActivity提及

做爲一個Android開發者,對startActivity(Intent intent)這個方法確定很熟悉,可是你瞭解他背後的啓動流程麼,這篇文章深刻源碼分析Activity的啓動流程。java

Activity

咱們一般調用startActivity()或者context.startActivity()都會走到Activity的startActivity,下面就是調用流程,注意到最終會調用Instrumentation.execStartActivity。android

@Override
    public void startActivity(Intent intent) {
        this.startActivity(intent, null);
    }

    @Override
    public void startActivity(Intent intent, @Nullable Bundle options) {
        if (options != null) {
            startActivityForResult(intent, -1, options);
        } else {
            // Note we want to go through this call for compatibility with
            // applications that may have overridden the method.
            startActivityForResult(intent, -1);
        }
    }

    public void startActivityForResult(@RequiresPermission Intent intent, int requestCode) {
        startActivityForResult(intent, requestCode, null);
    }

    public void startActivityForResult(@RequiresPermission Intent intent, int requestCode, @Nullable Bundle options) {
        if (mParent == null) {
            options = transferSpringboardActivityOptions(options);
            Instrumentation.ActivityResult ar =
                mInstrumentation.execStartActivity(
                    this, mMainThread.getApplicationThread(), mToken, this,
                    intent, requestCode, options);
            if (ar != null) {
                mMainThread.sendActivityResult(
                    mToken, mEmbeddedID, requestCode, ar.getResultCode(),
                    ar.getResultData());
            }
            if (requestCode >= 0) {
                // If this start is requesting a result, we can avoid making
                // the activity visible until the result is received. Setting
                // this code during onCreate(Bundle savedInstanceState) or onResume() will keep the
                // activity hidden during this time, to avoid flickering.
                // This can only be done when a result is requested because
                // that guarantees we will get information back when the
                // activity is finished, no matter what happens to it.
                mStartedActivity = true;
            }

            cancelInputsAndStartExitTransition(options);
            // TODO Consider clearing/flushing other event sources and events for child windows.
        } else {
            if (options != null) {
                mParent.startActivityFromChild(this, intent, requestCode, options);
            } else {
                // Note we want to go through this method for compatibility with
                // existing applications that may have overridden it.
                mParent.startActivityFromChild(this, intent, requestCode);
            }
        }
    }
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Instrumentation

(android/app/Instrumentation)windows

根據源碼中的註釋咱們能夠知道:這是一個實現應用程序監控代碼的基類,若是一個應用程序打開了監控開關來運行,那麼這個類將會在全部應用程序代碼執行前進行實例化,以便容許咱們監控系統與應用程序之間的互相做用。咱們能夠在AndroidManifest.xml中用instrumentation來指定應用程序使用哪個具體實現。app

咱們來看execStartActivity方法的實現,它調用了ActivityManagerNative.getDefault().startActivity(),繼續往下跟到ActivityManagerNativeide

public ActivityResult execStartActivity( Context who, IBinder contextThread, IBinder token, Activity target, Intent intent, int requestCode, Bundle options) {
        IApplicationThread whoThread = (IApplicationThread) contextThread;
        Uri referrer = target != null ? target.onProvideReferrer() : null;
        if (referrer != null) {
            intent.putExtra(Intent.EXTRA_REFERRER, referrer);
        }
        ...
        try {
            intent.migrateExtraStreamToClipData();
            intent.prepareToLeaveProcess(who);
            int result = ActivityManagerNative.getDefault()
                .startActivity(whoThread, who.getBasePackageName(), intent,
                        intent.resolveTypeIfNeeded(who.getContentResolver()),
                        token, target != null ? target.mEmbeddedID : null,
                        requestCode, 0, null, options);
            checkStartActivityResult(result, intent);
        } catch (RemoteException e) {
            throw new RuntimeException("Failure from system", e);
        }
        return null;
    }
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ActivityManagerNative

(android/app)oop

ActivityManagerNative繼承了Binder,並實現了IActivityManager,而IActivityManager繼承於IInterface,也就是說這個類是用於進程間通訊的,咱們看getDefault()方法,其實他最終返回了一個ActivityManagerProxy對象,並把ActivityManagerService傳給它。咱們知道Binder做爲Android上進程間通訊的實現方案,它實際上是相似於客戶端與服務端交互這樣一個模型的,而ActivityManagerService就至關於服務端,它在系統啓動的時候就會啓動,做爲一個單獨的服務進程運行,而ActivityManagerProxy至關於client端與server端交互的一個代理。源碼分析

static public IActivityManager getDefault() {
        return gDefault.get();
    }

    private static final Singleton<IActivityManager> gDefault = new Singleton<IActivityManager>() {
        protected IActivityManager create() {
            //獲得ActivityManagerService,繼承於ActivityManagerNative
            IBinder b = ServiceManager.getService("activity");
            IActivityManager am = asInterface(b);
            return am;
        }
    };

    static public IActivityManager asInterface(IBinder obj) {
        if (obj == null) {
            return null;
        }
        IActivityManager in =
            (IActivityManager)obj.queryLocalInterface(descriptor);
        if (in != null) {
            return in;
        }
        return new ActivityManagerProxy(obj);
    }

 @Override
    public boolean onTransact(int code, Parcel data, Parcel reply, int flags) throws RemoteException {
        switch (code) {
        case START_ACTIVITY_TRANSACTION:
        {
            data.enforceInterface(IActivityManager.descriptor);
            IBinder b = data.readStrongBinder();
            IApplicationThread app = ApplicationThreadNative.asInterface(b);
            String callingPackage = data.readString();
            Intent intent = Intent.CREATOR.createFromParcel(data);
            String resolvedType = data.readString();
            IBinder resultTo = data.readStrongBinder();
            String resultWho = data.readString();
            int requestCode = data.readInt();
            int startFlags = data.readInt();
            ProfilerInfo profilerInfo = data.readInt() != 0
                    ? ProfilerInfo.CREATOR.createFromParcel(data) : null;
            Bundle options = data.readInt() != 0
                    ? Bundle.CREATOR.createFromParcel(data) : null;
            int result = startActivity(app, callingPackage, intent, resolvedType,
                    resultTo, resultWho, requestCode, startFlags, profilerInfo, options);
            reply.writeNoException();
            reply.writeInt(result);
            return true;
        }
        ...
    }
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ActivityManagerProxy,它是ActivityManagerNative的一個內部類,它持有一個IBinder對象,而ActivityManagerNative的asInterface方法初始化它是給他傳的是ActivityManagerService,在調用它的startActivity時調用了mRemote.transact(START_ACTIVITY_TRANSACTION, data, reply, 0),而ActivityManagerService繼承於ActivityManagerNative而且沒有重寫onTransact方法所以調用ActivityManagerNative的onTransact,具體見上面的代碼,在onTransact裏面會調用startActivity方法,由於當前對象是ActivityManagerService類型,所以調用ActivityManagerService裏面的startActivity方法。post

public int startActivity(IApplicationThread caller, String callingPackage, Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode, int startFlags, ProfilerInfo profilerInfo, Bundle options) throws RemoteException {
        Parcel data = Parcel.obtain();
        Parcel reply = Parcel.obtain();
        data.writeInterfaceToken(IActivityManager.descriptor);
        data.writeStrongBinder(caller != null ? caller.asBinder() : null);
        data.writeString(callingPackage);
        intent.writeToParcel(data, 0);
        data.writeString(resolvedType);
        data.writeStrongBinder(resultTo);
        data.writeString(resultWho);
        data.writeInt(requestCode);
        data.writeInt(startFlags);
        if (profilerInfo != null) {
            data.writeInt(1);
            profilerInfo.writeToParcel(data, Parcelable.PARCELABLE_WRITE_RETURN_VALUE);
        } else {
            data.writeInt(0);
        }
        if (options != null) {
            data.writeInt(1);
            options.writeToParcel(data, 0);
        } else {
            data.writeInt(0);
        }
        mRemote.transact(START_ACTIVITY_TRANSACTION, data, reply, 0);
        reply.readException();
        int result = reply.readInt();
        reply.recycle();
        data.recycle();
        return result;
    }
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ActivityManagerService

(com/android/server/am)ui

@Override
    public final int startActivity(IApplicationThread caller, String callingPackage, Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode, int startFlags, ProfilerInfo profilerInfo, Bundle bOptions) {
        return startActivityAsUser(caller, callingPackage, intent, resolvedType, resultTo,
                resultWho, requestCode, startFlags, profilerInfo, bOptions,
                UserHandle.getCallingUserId());
    }
    @Override
    public final int startActivityAsUser(IApplicationThread caller, String callingPackage, Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode, int startFlags, ProfilerInfo profilerInfo, Bundle bOptions, int userId) {
        enforceNotIsolatedCaller("startActivity");
        userId = mUserController.handleIncomingUser(Binder.getCallingPid(), Binder.getCallingUid(),
                userId, false, ALLOW_FULL_ONLY, "startActivity", null);
        // TODO: Switch to user app stacks here.
        return mActivityStarter.startActivityMayWait(caller, -1, callingPackage, intent,
                resolvedType, null, null, resultTo, resultWho, requestCode, startFlags,
                profilerInfo, null, null, bOptions, false, userId, null, null);
    }
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最終調用了ActivityStarter.startActivityMayWait()this

ActivityStarter

(com/android/server/am)

下面就正式進入了Activity的啓動流程了,代碼會比較多,邏輯也比較複雜

final int startActivityMayWait(IApplicationThread caller, int callingUid, String callingPackage, Intent intent, String resolvedType, IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor, IBinder resultTo, String resultWho, int requestCode, int startFlags, ProfilerInfo profilerInfo, IActivityManager.WaitResult outResult, Configuration config, Bundle bOptions, boolean ignoreTargetSecurity, int userId, IActivityContainer iContainer, TaskRecord inTask) {
        // Refuse possible leaked file descriptors
        if (intent != null && intent.hasFileDescriptors()) {
            throw new IllegalArgumentException("File descriptors passed in Intent");
        }
        mSupervisor.mActivityMetricsLogger.notifyActivityLaunching();
        boolean componentSpecified = intent.getComponent() != null;

        // Save a copy in case ephemeral needs it
        final Intent ephemeralIntent = new Intent(intent);
        // Don't modify the client's object!
        intent = new Intent(intent);

        ResolveInfo rInfo = mSupervisor.resolveIntent(intent, resolvedType, userId);
        ...
        // (蒐集Intent的目標信息)Collect information about the target of the Intent.
        ActivityInfo aInfo = mSupervisor.resolveActivity(intent, rInfo, startFlags, profilerInfo);

        ActivityOptions options = ActivityOptions.fromBundle(bOptions);
        ActivityStackSupervisor.ActivityContainer container =
                (ActivityStackSupervisor.ActivityContainer)iContainer;
        synchronized (mService) {
			...
            final ActivityRecord[] outRecord = new ActivityRecord[1];
            int res = startActivityLocked(caller, intent, ephemeralIntent, resolvedType,
                    aInfo, rInfo, voiceSession, voiceInteractor,
                    resultTo, resultWho, requestCode, callingPid,
                    callingUid, callingPackage, realCallingPid, realCallingUid, startFlags,
                    options, ignoreTargetSecurity, componentSpecified, outRecord, container,
                    inTask);
			...
            return res;
        }
    }

    final int startActivityLocked(IApplicationThread caller, Intent intent, Intent ephemeralIntent, String resolvedType, ActivityInfo aInfo, ResolveInfo rInfo, IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor, IBinder resultTo, String resultWho, int requestCode, int callingPid, int callingUid, String callingPackage, int realCallingPid, int realCallingUid, int startFlags, ActivityOptions options, boolean ignoreTargetSecurity, boolean componentSpecified, ActivityRecord[] outActivity, ActivityStackSupervisor.ActivityContainer container, TaskRecord inTask) {
        int err = ActivityManager.START_SUCCESS;

        if ((launchFlags & Intent.FLAG_ACTIVITY_FORWARD_RESULT) != 0 && sourceRecord != null) {
            // Transfer the result target from the source activity to the new
            // one being started, including any failures.
            if (requestCode >= 0) {
                ActivityOptions.abort(options);
                return ActivityManager.START_FORWARD_AND_REQUEST_CONFLICT;
            }
            resultRecord = sourceRecord.resultTo;
            if (resultRecord != null && !resultRecord.isInStackLocked()) {
                resultRecord = null;
            }
            resultWho = sourceRecord.resultWho;
            requestCode = sourceRecord.requestCode;
            sourceRecord.resultTo = null;
            if (resultRecord != null) {
                resultRecord.removeResultsLocked(sourceRecord, resultWho, requestCode);
            }
            if (sourceRecord.launchedFromUid == callingUid) {
                // The new activity is being launched from the same uid as the previous
                // activity in the flow, and asking to forward its result back to the
                // previous. In this case the activity is serving as a trampoline between
                // the two, so we also want to update its launchedFromPackage to be the
                // same as the previous activity. Note that this is safe, since we know
                // these two packages come from the same uid; the caller could just as
                // well have supplied that same package name itself. This specifially
                // deals with the case of an intent picker/chooser being launched in the app
                // flow to redirect to an activity picked by the user, where we want the final
                // activity to consider it to have been launched by the previous app activity.
                callingPackage = sourceRecord.launchedFromPackage;
            }
        }

        ActivityRecord r = new ActivityRecord(mService, callerApp, callingUid, callingPackage,
                intent, resolvedType, aInfo, mService.mConfiguration, resultRecord, resultWho,
                requestCode, componentSpecified, voiceSession != null, mSupervisor, container,
                options, sourceRecord);
        if (outActivity != null) {
            outActivity[0] = r;
        }

        if (r.appTimeTracker == null && sourceRecord != null) {
            // If the caller didn't specify an explicit time tracker, we want to continue
            // tracking under any it has.
            r.appTimeTracker = sourceRecord.appTimeTracker;
        }

        final ActivityStack stack = mSupervisor.mFocusedStack;

        doPendingActivityLaunchesLocked(false);

        try {
            mService.mWindowManager.deferSurfaceLayout();
            err = startActivityUnchecked(r, sourceRecord, voiceSession, voiceInteractor, startFlags,
                    true, options, inTask);
        } finally {
            mService.mWindowManager.continueSurfaceLayout();
        }
        postStartActivityUncheckedProcessing(r, err, stack.mStackId, mSourceRecord, mTargetStack);
        return err;
    }

    private int startActivityUnchecked(final ActivityRecord r, ActivityRecord sourceRecord, IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor, int startFlags, boolean doResume, ActivityOptions options, TaskRecord inTask) {
		...
        mTargetStack.startActivityLocked(mStartActivity, newTask, mKeepCurTransition, mOptions);
        if (mDoResume) {
            final ActivityRecord topTaskActivity = mStartActivity.task.topRunningActivityLocked();
            if (!mTargetStack.isFocusable()
                    || (topTaskActivity != null && topTaskActivity.mTaskOverlay
                    && mStartActivity != topTaskActivity)) {
                // If the activity is not focusable, we can't resume it, but still would like to
                // make sure it becomes visible as it starts (this will also trigger entry
                // animation). An example of this are PIP activities.
                // Also, we don't want to resume activities in a task that currently has an overlay
                // as the starting activity just needs to be in the visible paused state until the
                // over is removed.
                mTargetStack.ensureActivitiesVisibleLocked(null, 0, !PRESERVE_WINDOWS);
                // Go ahead and tell window manager to execute app transition for this activity
                // since the app transition will not be triggered through the resume channel.
                mWindowManager.executeAppTransition();
            } else {
                mSupervisor.resumeFocusedStackTopActivityLocked(mTargetStack, mStartActivity,
                        mOptions);
            }
        } 
        ...
        return START_SUCCESS;
    }
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通過一系列的對Intent的解析,以及對Activity的LaunchMode的判斷,最終,調用了ActivityStackSupervisor.resumeFocusedStackTopActivityLocked()方法。

ActivityStackSupervisor

(com/android/server/am)

boolean resumeFocusedStackTopActivityLocked( ActivityStack targetStack, ActivityRecord target, ActivityOptions targetOptions) {
        if (targetStack != null && isFocusedStack(targetStack)) {
            return targetStack.resumeTopActivityUncheckedLocked(target, targetOptions);
        }
        final ActivityRecord r = mFocusedStack.topRunningActivityLocked();
        if (r == null || r.state != RESUMED) {
            mFocusedStack.resumeTopActivityUncheckedLocked(null, null);
        }
        return false;
    }
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ActivityStack

(com/android/server/am)

boolean resumeTopActivityUncheckedLocked(ActivityRecord prev, ActivityOptions options) {
        if (mStackSupervisor.inResumeTopActivity) {
            // Don't even start recursing.
            return false;
        }

        boolean result = false;
        try {
            // Protect against recursion.
            mStackSupervisor.inResumeTopActivity = true;
            if (mService.mLockScreenShown == ActivityManagerService.LOCK_SCREEN_LEAVING) {
                mService.mLockScreenShown = ActivityManagerService.LOCK_SCREEN_HIDDEN;
                mService.updateSleepIfNeededLocked();
            }
            result = resumeTopActivityInnerLocked(prev, options);
        } finally {
            mStackSupervisor.inResumeTopActivity = false;
        }
        return result;
    }
private boolean resumeTopActivityInnerLocked(ActivityRecord prev, ActivityOptions options) {
		...

        if (next.app != null && next.app.thread != null) {
                     //若是當前Activity在棧中已經存在實例,那麼直接經過調用 next.app.thread.scheduleResumeActivity讓其resume,
				...
                next.app.thread.scheduleResumeActivity(next.appToken, next.app.repProcState,
                        mService.isNextTransitionForward(), resumeAnimOptions);

                mStackSupervisor.checkReadyForSleepLocked();

                if (DEBUG_STATES) Slog.d(TAG_STATES, "resumeTopActivityLocked: Resumed " + next);
            }

        } else {
    		//不然走這裏
            mStackSupervisor.startSpecificActivityLocked(next, true, true);
        }

        return true;
    }

ActivityStackSupervisor void startSpecificActivityLocked(ActivityRecord r, boolean andResume, boolean checkConfig) {
        // Is this activity's application already running?
        ProcessRecord app = mService.getProcessRecordLocked(r.processName,
                r.info.applicationInfo.uid, true);

        r.task.stack.setLaunchTime(r);

        if (app != null && app.thread != null) {
            //若是進程已存在並正在運行,直接經過realStartActivityLocked啓動Activity
            try {
                if ((r.info.flags&ActivityInfo.FLAG_MULTIPROCESS) == 0
                        || !"android".equals(r.info.packageName)) {
                    app.addPackage(r.info.packageName, r.info.applicationInfo.versionCode,
                            mService.mProcessStats);
                }
                realStartActivityLocked(r, app, andResume, checkConfig);
                return;
            } catch (RemoteException e) {
            }

        }
        //不然調用ActivityManagerService開啓新進程
        mService.startProcessLocked(r.processName, r.info.applicationInfo, true, 0,
                "activity", r.intent.getComponent(), false, false, true);
    }

ActivityStackSupervisor final boolean realStartActivityLocked(ActivityRecord r, ProcessRecord app, boolean andResume, boolean checkConfig) throws RemoteException {
			...
            app.forceProcessStateUpTo(mService.mTopProcessState);
            app.thread.scheduleLaunchActivity(new Intent(r.intent), r.appToken,
                    System.identityHashCode(r), r.info, new Configuration(mService.mConfiguration),
                    new Configuration(task.mOverrideConfig), r.compat, r.launchedFromPackage,
                    task.voiceInteractor, app.repProcState, r.icicle, r.persistentState, results,
                    newIntents, !andResume, mService.isNextTransitionForward(), profilerInfo);
			... 

        return true;
    }

ActivityManagerService private final void startProcessLocked(ProcessRecord app, String hostingType, String hostingNameStr, String abiOverride, String entryPoint, String[] entryPointArgs) {
	            boolean isActivityProcess = (entryPoint == null);
            if (entryPoint == null) entryPoint = "android.app.ActivityThread";
            Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "Start proc: " +
                    app.processName);
            checkTime(startTime, "startProcess: asking zygote to start proc");
            Process.ProcessStartResult startResult = Process.start(entryPoint,
                    app.processName, uid, uid, gids, debugFlags, mountExternal,
                    app.info.targetSdkVersion, app.info.seinfo, requiredAbi, instructionSet,
                    app.info.dataDir, entryPointArgs);
}
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啓動進程的時候entryPoint表明進程啓動時的入口類,會調用該類的main方法,這裏指定爲ActivityThread類,也就是說,當進程啓動後,會調用ActivityThread的main方法,那麼咱們看看這個類都作了些什麼

ActivityThread

public static void main(String[] args) {
		...
        Looper.prepareMainLooper();

        ActivityThread thread = new ActivityThread();
        thread.attach(false);

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

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

  private void attach(boolean system) {
        sCurrentActivityThread = this;
        mSystemThread = system;
        if (!system) {
            final IActivityManager mgr = ActivityManagerNative.getDefault();
            try {
                mgr.attachApplication(mAppThread);
            } catch (RemoteException ex) {
                throw ex.rethrowFromSystemServer();
            }
        }
      ...
    }

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也就是說進程啓動後會調用ActivityManagerService的attachApplication方法,並把當前的ApplicationThread的對象傳過去,ApplicationThread是ActivityThread的一個內部類,而前面頻繁出現的app.thread其實就是該類的實例,調用它的scheduleLaunchActivity,scheduleResumeActivity等方法會經過handler把消息傳遞給ActivityThread中的handler來進行後續操做。下面咱們繼續看ActivityManagerService的attachApplication方法:

@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) {
        
        // See if the top visible activity is waiting to run in this process...
        if (normalMode) {
            try {
                if (mStackSupervisor.attachApplicationLocked(app)) {
                    didSomething = true;
                }
            } catch (Exception e) {
                Slog.wtf(TAG, "Exception thrown launching activities in " + app, e);
                badApp = true;
            }
        }
    }

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當有Activity等待啓動的時候,調用ActivityStackSupervisor的attachApplicationLocked的方法,該方法內部調用了realStartActivityLocked來啓動Activity。根據上面的代碼,咱們知道realStartActivityLocked調用了app.thread.scheduleLaunchActivity也就是調用了ApplicationThread中的scheduleLaunchActivity方法,那麼咱們去看下該方法的具體實現

// we use token to identify this activity without having to send the
        // activity itself back to the activity manager. (matters more with ipc)
        @Override
        public final void scheduleLaunchActivity(Intent intent, IBinder token, int ident, ActivityInfo info, Configuration curConfig, Configuration overrideConfig, CompatibilityInfo compatInfo, String referrer, IVoiceInteractor voiceInteractor, int procState, Bundle state, PersistableBundle persistentState, List<ResultInfo> pendingResults, List<ReferrerIntent> pendingNewIntents, boolean notResumed, boolean isForward, ProfilerInfo profilerInfo) {

            updateProcessState(procState, false);

            ActivityClientRecord r = new ActivityClientRecord();
			...
            sendMessage(H.LAUNCH_ACTIVITY, r);
        }

複製代碼

sendMessage向ActivityThread中的H發送一條消息

public void handleMessage(Message msg) {
            if (DEBUG_MESSAGES) Slog.v(TAG, ">>> handling: " + codeToString(msg.what));
            switch (msg.what) {
                case LAUNCH_ACTIVITY: {
                    Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityStart");
                    final ActivityClientRecord r = (ActivityClientRecord) msg.obj;

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

   private void handleLaunchActivity(ActivityClientRecord r, Intent customIntent, String reason) {

        Activity a = performLaunchActivity(r, customIntent);

        if (a != null) {
            r.createdConfig = new Configuration(mConfiguration);
            reportSizeConfigurations(r);
            Bundle oldState = r.state;
            handleResumeActivity(r.token, false, r.isForward,
                    !r.activity.mFinished && !r.startsNotResumed, r.lastProcessedSeq, reason);
        } else {
            // 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,
                            Activity.DONT_FINISH_TASK_WITH_ACTIVITY);
            } catch (RemoteException ex) {
                throw ex.rethrowFromSystemServer();
            }
        }
    }

複製代碼

performLaunchActivity中主要就是經過前面的Instrumentation建立Activity對象並調用相關生命週期方法。

startActivity流程到這裏基本已經結束了,固然區中還有一些輔助類,好比ActivityStack等來配合Activity的入棧出棧工做,咱們沒有作詳細分析,有興趣能夠再詳細看一下相關源碼。

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