Activity启动流程源码解析（原创）

1、Activity启动流程

原帖地址
我的GitHub

Intent intent=new Intent(this,activity.class);startActivity(intent);

1. 通过以上代码将会启动一个Activity，startActivity方法会有好几种重载方式，但是他们最终都会调用startActivityForResult方法，实现如下：

    public void startActivityForResult(Intent intent, int requestCode, Bundle options) {        if (mParent == null) {            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;            }        } 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);            }        }    }

我们只需关注mParent==null这部分，mParent代表的是ActivityGroup，一开始被用来嵌入多个Activity，但是API13已经被废弃了，系统目前采用的都是Fragment代替ActivityGroup。然后调用mInstrumentation.execStartActivity方法，方法的参数中的mMainThread.getApplicationThread()类型是ApplicationThread,ApplicationThread是ActivityThread的一个内部类。
2. mInstrumentation.execStartActivity:

    public ActivityResult execStartActivity(            Context who, IBinder contextThread, IBinder token, Activity target,            Intent intent, int requestCode, Bundle options) {        IApplicationThread whoThread = (IApplicationThread) contextThread;        if (mActivityMonitors != null) {            synchronized (mSync) {                final int N = mActivityMonitors.size();                for (int i=0; i<N; i++) {                    final ActivityMonitor am = mActivityMonitors.get(i);                    if (am.match(who, null, intent)) {                        am.mHits++;                        if (am.isBlocking()) {                            return requestCode >= 0 ? am.getResult() : null;                        }                        break;                    }                }            }        }        try {            intent.migrateExtraStreamToClipData();            intent.prepareToLeaveProcess();            int result = ActivityManagerNative.getDefault()                .startActivity(whoThread, who.getBasePackageName(), intent,                        intent.resolveTypeIfNeeded(who.getContentResolver()),                        token, target != null ? target.mEmbeddedID : null,                        requestCode, 0, null, null, options);            checkStartActivityResult(result, intent);        } catch (RemoteException e) {        }        return null;

可以看到，启动Activity的真正实现是由ActivityManagerNative.getDefault()
.startActivity实现的，AMS继承自ActivityManagerNative，ActivityManagerNative.getDefault()是一个AMS，采用单例模式提供对象，第一次调用会通过creat方法初始化AMS，然后后续调用直接返回即可。
3. AMS的startActivity方法

    public final int startActivity(IApplicationThread caller, String callingPackage,            Intent intent, String resolvedType, IBinder resultTo,            String resultWho, int requestCode, int startFlags,            String profileFile, ParcelFileDescriptor profileFd, Bundle options) {        return startActivityAsUser(caller, callingPackage, intent, resolvedType, resultTo,                resultWho, requestCode,                startFlags, profileFile, profileFd, options, UserHandle.getCallingUserId());    }

1. startActivity转移到了startActivityAsUser中

    public final int startActivityAsUser(IApplicationThread caller, String callingPackage,            Intent intent, String resolvedType, IBinder resultTo,            String resultWho, int requestCode, int startFlags,            String profileFile, ParcelFileDescriptor profileFd, Bundle options, int userId) {        enforceNotIsolatedCaller("startActivity");        userId = handleIncomingUser(Binder.getCallingPid(), Binder.getCallingUid(), userId,                false, true, "startActivity", null);        return mMainStack.startActivityMayWait(caller, -1, callingPackage, intent, resolvedType,                resultTo, resultWho, requestCode, startFlags, profileFile, profileFd,                null, null, options, userId);    }

1. 转移到了ActivityStack的mMainStack.startActivityMayWait中，

 int res = startActivityLocked(caller, intent, resolvedType,                    aInfo, resultTo, resultWho, requestCode, callingPid, callingUid,                    callingPackage, startFlags, options, componentSpecified, null);

1. mMainStack.startActivityMayWait方法中调用了startActivityLocked方法。

    err = startActivityUncheckedLocked(r, sourceRecord,                startFlags, true, options);

1. startActivityLocked方法调用startActivityUncheckedLocked方法

resumeTopActivityLocked(null, options);

1. 接着调用resumeTopActivityLocked

startSpecificActivityLocked(next, true, false);

1. 接着调用startSpecificActivityLocked

        if (app != null && app.thread != null) {            try {                app.addPackage(r.info.packageName);                realStartActivityLocked(r, app, andResume, checkConfig);                return;            } catch (RemoteException e) {                Slog.w(TAG, "Exception when starting activity "                        + r.intent.getComponent().flattenToShortString(), e);            }            // If a dead object exception was thrown -- fall through to            // restart the application.        }

1. 接着调用realStartActivityLocked方法，

app.thread.scheduleLaunchActivity(new Intent(r.intent), r.appToken,                    System.identityHashCode(r), r.info,                    new Configuration(mService.mConfiguration),                    r.compat, r.icicle, results, newIntents, !andResume,                    mService.isNextTransitionForward(), profileFile, profileFd,                    profileAutoStop);

1. realStartActivityLocked中有一句：app.thread.scheduleLaunchActivity，app.thread类型为IApplicationThread，IApplicationThread的实现类为ApplicationThread，即调用的是ApplicationThread的scheduleLaunchActivity：

        public final void scheduleLaunchActivity(Intent intent, IBinder token, int ident,                ActivityInfo info, Configuration curConfig, CompatibilityInfo compatInfo,                Bundle state, List<ResultInfo> pendingResults,                List<Intent> 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);            queueOrSendMessage(H.LAUNCH_ACTIVITY, r);        }

1. scheduleLaunchActivity发送一个H.LAUNCH_ACTIVITY的消息来交给Handler处理，Handler H的代码如下：

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;                case RELAUNCH_ACTIVITY: {                    Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityRestart");                    ActivityClientRecord r = (ActivityClientRecord)msg.obj;                    handleRelaunchActivity(r);                    Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);                } break;                case PAUSE_ACTIVITY:                    Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityPause");                    handlePauseActivity((IBinder)msg.obj, false, msg.arg1 != 0, msg.arg2);                    maybeSnapshot();                    Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);                    break;                case PAUSE_ACTIVITY_FINISHING:                    Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityPause");                    handlePauseActivity((IBinder)msg.obj, true, msg.arg1 != 0, msg.arg2);                    Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);                    break;                case STOP_ACTIVITY_SHOW:                    Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityStop");                    handleStopActivity((IBinder)msg.obj, true, msg.arg2);                    Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);                    break;                case STOP_ACTIVITY_HIDE:                    Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityStop");                    handleStopActivity((IBinder)msg.obj, false, msg.arg2);                    Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);                    break;                case SHOW_WINDOW:                    Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityShowWindow");                    handleWindowVisibility((IBinder)msg.obj, true);                    Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);                    break;                case HIDE_WINDOW:                    Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityHideWindow");                    handleWindowVisibility((IBinder)msg.obj, false);                    Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);                    break;                case RESUME_ACTIVITY:                    Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityResume");                    handleResumeActivity((IBinder)msg.obj, true,                            msg.arg1 != 0, true);                    Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);                    break;                case SEND_RESULT:                    Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityDeliverResult");                    handleSendResult((ResultData)msg.obj);                    Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);                    break;                case DESTROY_ACTIVITY:                    Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityDestroy");                    handleDestroyActivity((IBinder)msg.obj, msg.arg1 != 0,                            msg.arg2, false);                    Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);                    break;                case BIND_APPLICATION:                    Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "bindApplication");                    AppBindData data = (AppBindData)msg.obj;                    handleBindApplication(data);                    Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);                    break;                case EXIT_APPLICATION:                    if (mInitialApplication != null) {                        mInitialApplication.onTerminate();                    }                    Looper.myLooper().quit();                    break;                case NEW_INTENT:                    Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityNewIntent");                    handleNewIntent((NewIntentData)msg.obj);                    Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);                    break;                case RECEIVER:                    Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "broadcastReceiveComp");                    handleReceiver((ReceiverData)msg.obj);                    maybeSnapshot();                    Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);                    break;                case CREATE_SERVICE:                    Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "serviceCreate");                    handleCreateService((CreateServiceData)msg.obj);                    Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);                    break;                case BIND_SERVICE:                    Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "serviceBind");                    handleBindService((BindServiceData)msg.obj);                    Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);                    break;                case UNBIND_SERVICE:                    Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "serviceUnbind");                    handleUnbindService((BindServiceData)msg.obj);                    Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);                    break;                case SERVICE_ARGS:                    Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "serviceStart");                    handleServiceArgs((ServiceArgsData)msg.obj);                    Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);                    break;                case STOP_SERVICE:                    Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "serviceStop");                    handleStopService((IBinder)msg.obj);                    maybeSnapshot();                    Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);                    break;                case REQUEST_THUMBNAIL:                    Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "requestThumbnail");                    handleRequestThumbnail((IBinder)msg.obj);                    Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);                    break;                case CONFIGURATION_CHANGED:                    Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "configChanged");                    mCurDefaultDisplayDpi = ((Configuration)msg.obj).densityDpi;                    handleConfigurationChanged((Configuration)msg.obj, null);                    Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);                    break;                case CLEAN_UP_CONTEXT:                    ContextCleanupInfo cci = (ContextCleanupInfo)msg.obj;                    cci.context.performFinalCleanup(cci.who, cci.what);                    break;                case GC_WHEN_IDLE:                    scheduleGcIdler();                    break;                case DUMP_SERVICE:                    handleDumpService((DumpComponentInfo)msg.obj);                    break;                case LOW_MEMORY:                    Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "lowMemory");                    handleLowMemory();                    Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);                    break;                case ACTIVITY_CONFIGURATION_CHANGED:                    Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityConfigChanged");                    handleActivityConfigurationChanged((IBinder)msg.obj);                    Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);                    break;                case PROFILER_CONTROL:                    handleProfilerControl(msg.arg1 != 0, (ProfilerControlData)msg.obj, msg.arg2);                    break;                case CREATE_BACKUP_AGENT:                    Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "backupCreateAgent");                    handleCreateBackupAgent((CreateBackupAgentData)msg.obj);                    Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);                    break;                case DESTROY_BACKUP_AGENT:                    Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "backupDestroyAgent");                    handleDestroyBackupAgent((CreateBackupAgentData)msg.obj);                    Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);                    break;                case SUICIDE:                    Process.killProcess(Process.myPid());                    break;                case REMOVE_PROVIDER:                    Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "providerRemove");                    completeRemoveProvider((ProviderRefCount)msg.obj);                    Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);                    break;                case ENABLE_JIT:                    ensureJitEnabled();                    break;                case DISPATCH_PACKAGE_BROADCAST:                    Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "broadcastPackage");                    handleDispatchPackageBroadcast(msg.arg1, (String[])msg.obj);                    Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);                    break;                case SCHEDULE_CRASH:                    throw new RemoteServiceException((String)msg.obj);                case DUMP_HEAP:                    handleDumpHeap(msg.arg1 != 0, (DumpHeapData)msg.obj);                    break;                case DUMP_ACTIVITY:                    handleDumpActivity((DumpComponentInfo)msg.obj);                    break;                case DUMP_PROVIDER:                    handleDumpProvider((DumpComponentInfo)msg.obj);                    break;                case SLEEPING:                    Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "sleeping");                    handleSleeping((IBinder)msg.obj, msg.arg1 != 0);                    Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);                    break;                case SET_CORE_SETTINGS:                    Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "setCoreSettings");                    handleSetCoreSettings((Bundle) msg.obj);                    Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);                    break;                case UPDATE_PACKAGE_COMPATIBILITY_INFO:                    handleUpdatePackageCompatibilityInfo((UpdateCompatibilityData)msg.obj);                    break;                case TRIM_MEMORY:                    Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "trimMemory");                    handleTrimMemory(msg.arg1);                    Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);                    break;                case UNSTABLE_PROVIDER_DIED:                    handleUnstableProviderDied((IBinder)msg.obj, false);                    break;                case REQUEST_ACTIVITY_EXTRAS:                    handleRequestActivityExtras((RequestActivityExtras)msg.obj);                    break;            }            if (DEBUG_MESSAGES) Slog.v(TAG, "<<< done: " + codeToString(msg.what));        }

1. 调用ActivityThread的handleLaunchActivity(r, null)方法

Activity a = performLaunchActivity(r, customIntent);        if (a != null) {            r.createdConfig = new Configuration(mConfiguration);            Bundle oldState = r.state;            handleResumeActivity(r.token, false, r.isForward,                    !r.activity.mFinished && !r.startsNotResumed);

1. performLaunchActivity完成Activity对象的创建，handleResumeActivity完成Activity的onResume一系列方法。

2、performLaunchActivity的流程

1. 从ActiivtyClientRecord中获取Activity的组建信息

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);        }

1. 调用mInstrumentation.newActivity创建Activity

activity = mInstrumentation.newActivity(                    cl, component.getClassName(), r.intent);

    public Activity newActivity(ClassLoader cl, String className,            Intent intent)            throws InstantiationException, IllegalAccessException,            ClassNotFoundException {        return (Activity)cl.loadClass(className).newInstance();    }

通过类加载器来创建Activity
3. 通过LoadedApk的makeApplication方法创建Application

    public Application makeApplication(boolean forceDefaultAppClass,            Instrumentation instrumentation) {        if (mApplication != null) {            return mApplication;        }        Application app = null;        String appClass = mApplicationInfo.className;        if (forceDefaultAppClass || (appClass == null)) {            appClass = "android.app.Application";        }        try {            java.lang.ClassLoader cl = getClassLoader();            ContextImpl appContext = new ContextImpl();            appContext.init(this, null, mActivityThread);            app = mActivityThread.mInstrumentation.newApplication(                    cl, appClass, appContext);            appContext.setOuterContext(app);        } catch (Exception e) {            if (!mActivityThread.mInstrumentation.onException(app, e)) {                throw new RuntimeException(                    "Unable to instantiate application " + appClass                    + ": " + e.toString(), e);            }        }        mActivityThread.mAllApplications.add(app);        mApplication = app;        if (instrumentation != null) {            try {                instrumentation.callApplicationOnCreate(app);            } catch (Exception e) {                if (!instrumentation.onException(app, e)) {                    throw new RuntimeException(                        "Unable to create application " + app.getClass().getName()                        + ": " + e.toString(), e);                }            }        }        return app;

里面有以下代码

app = mActivityThread.mInstrumentation.newApplication(                    cl, appClass, appContext);

    public Application newApplication(ClassLoader cl, String className, Context context)            throws InstantiationException, IllegalAccessException,             ClassNotFoundException {        return newApplication(cl.loadClass(className), context);    }

可以看到也是通过类加载器来加载Application的，然后调用zai makeApplication方法中调用Application的onCreate方法了

instrumentation.callApplicationOnCreate(app);

1. 调用Activity的onCreate

mInstrumentation.callActivityOnCreate(activity, r.state);

完成！
原帖地址
我的GitHub