Activity启动过程分析

Android的四大组件中除了BroadCastReceiver以外,其他三种组件都必须在AndroidManifest中注册,对于BroadCastReceiver来说,它既可以在AndroidManifest中注册也可以通过代码来注册,在调用方式上,Activity、Service和BroadCastReceiver需要借助Intent,而ContentProvider则无需借助Intent。

Activity是一种展示型组件,用于向用户直接展示一个界面,并且可以接收用户的输入信息从而进行交互,对于用户来说,Activity就是一个Android应用的全部,这是因为其他三大组件对用户来说都是不可感知的。Activity的启动由Intent触发,其中Intent可以分为显式Intent和隐式Intent,显式Intent可以明确地指向一个Activity组件,隐式Intent则指向一个或多个目标Activity组件,当然也有可能没有一个Activity组件处理这个Intent。

Activity的工作过程

要分析Activity的启动过程,就需要从startActivity方法开始分析,startActivity方法有好几种重载方式,但是最终都会调用startActivityForResult方法,具体代码如下:

/**
     * @hide
     */
    @Override
    public void startActivityForResult(
            String who, Intent intent, int requestCode, @Nullable Bundle options) {
        Uri referrer = onProvideReferrer();
        if (referrer != null) {
            intent.putExtra(Intent.EXTRA_REFERRER, referrer);
        }
        options = transferSpringboardActivityOptions(options);
        Instrumentation.ActivityResult ar =
            mInstrumentation.execStartActivity(
                this, mMainThread.getApplicationThread(), mToken, who,
                intent, requestCode, options);
        if (ar != null) {
            mMainThread.sendActivityResult(
                mToken, who, requestCode,
                ar.getResultCode(), ar.getResultData());
        }
        cancelInputsAndStartExitTransition(options);
    }

在上面代码中,要注意的是mMainThread.getApplicationThread()这个参数,它的类型是ApplicationThread,ApplicationThread是ActivityThread的一个内部类,其实可以知道的是,ApplicationThread和ActivityThread在Activity启动过程中发挥着重要的作用。然后看下 mInstrumentation.execStartActivity方法,代码如下:

 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);
        }
        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(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;
    }

从上面代码中可以看出,启动Activity真正的实现由ActivityManagerNative.getDefault()的startActivity方法来完成的,ActivityManagerService(简称AMS)继承自ActivityManagerNative,而ActivityManagerNative继承自Binder并实现了IActivityManager这个Binder接口,因此AMS也是一个Binder,它是IActivityManager的具体实现,其实ActivityManagerNative.getDefault()具体得到是AMS,在ActivityManagerNative中,AMS这个Binder对象采用单例模式对外提供,第一次调用它的get方法时它会通过create方法来初始化AMS这个Binder对象,在后续的调用中则直接返回之前创建的对象。这个过程源码如下:

    /**
     * Retrieve the system's default/global activity manager.
     */
    static public IActivityManager getDefault() {
        return gDefault.get();
    }

    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;
        }
    };

看到其中的源码,可以得知,Activity的启动过程又转移到AMS中,最终只需要分析AMS中的startActivity方法即可。同时,我们也在execStartActivity方法中看到这么一句:checkStartActivityResult(result, intent),直观应该是启动Activity的结果,具体实现如下:

 /** @hide */
    public static void checkStartActivityResult(int res, Object intent) {
        if (res >= ActivityManager.START_SUCCESS) {
            return;
        }

        switch (res) {
            case ActivityManager.START_INTENT_NOT_RESOLVED:
            case ActivityManager.START_CLASS_NOT_FOUND:
                if (intent instanceof Intent && ((Intent)intent).getComponent() != null)
                    throw new ActivityNotFoundException(
                            "Unable to find explicit activity class "
                            + ((Intent)intent).getComponent().toShortString()
                            + "; have you declared this activity in your AndroidManifest.xml?");
                throw new ActivityNotFoundException(
                        "No Activity found to handle " + intent);
            case ActivityManager.START_PERMISSION_DENIED:
                throw new SecurityException("Not allowed to start activity "
                        + intent);
            case ActivityManager.START_FORWARD_AND_REQUEST_CONFLICT:
                throw new AndroidRuntimeException(
                        "FORWARD_RESULT_FLAG used while also requesting a result");
            case ActivityManager.START_NOT_ACTIVITY:
                throw new IllegalArgumentException(
                        "PendingIntent is not an activity");
            case ActivityManager.START_NOT_VOICE_COMPATIBLE:
                throw new SecurityException(
                        "Starting under voice control not allowed for: " + intent);
            case ActivityManager.START_VOICE_NOT_ACTIVE_SESSION:
                throw new IllegalStateException(
                        "Session calling startVoiceActivity does not match active session");
            case ActivityManager.START_VOICE_HIDDEN_SESSION:
                throw new IllegalStateException(
                        "Cannot start voice activity on a hidden session");
            case ActivityManager.START_CANCELED:
                throw new AndroidRuntimeException("Activity could not be started for "
                        + intent);
            default:
                throw new AndroidRuntimeException("Unknown error code "
                        + res + " when starting " + intent);
        }
    }

作用很明显,就是检查启动Activity的结果,当无法正确地启动一个Activity时,这个方法会抛出异常信息,最熟悉的错误就是Unable to find explicit activity classhave you declared this activity in your AndroidManifest.xml?,当启动的Activity没有在AndroidManifest中注册时,就会抛出这个异常。

现在看AMS的startActivity这个方法:

    @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);
    }

从中可以看出,Activity的启动过程又转移到mActivityStarter.startActivityMayWait的方法上,在startActivityMayWait方法中又调用了startActivityLocked方法,然后startActivityLocked方法又调用了startActivityUncheckedLocked方法,最后调用了ActivityStack的resumeTopActivitiesLocked,此时启动过程转移到ActivityStack上。

总结一下,这其中走的流程图如下:

启动流程图

最终,通过源码分析,从IApplicationThread声明方法可以看出,内部包含了大量的启动、停止Activity的接口,此外还包含了启动和停止服务的接口。那么IApplicationThread的实现者到底是什么,答案就是ActivityThread内部的ApplicationThread,ApplicationThread的定义如下:

public interface IApplicationThread extends IInterface{
  ......//省略一部分代码
}

我们可以看到IInterface接口有个类型IBinder:

/**
 * Base class for Binder interfaces.  When defining a new interface,
 * you must derive it from IInterface.
 */
public interface IInterface
{
    /**
     * Retrieve the Binder object associated with this interface.
     * You must use this instead of a plain cast, so that proxy objects
     * can return the correct result.
     */
    public IBinder asBinder();
}

最终是通过Binder通信,系统为AIDL文件自动生成的代码,同时还有会一个ApplicationThreadProxy类,这个类其实AIDL文件自动生成的代理类,进而最终Activity的启动过程最终回到ApplicationThread中。ApplicationThread通过scheduleLaunchActivity方法启动Activity。

  // 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();

            r.token = token;
            r.ident = ident;
            r.intent = intent;
            r.referrer = referrer;
            r.voiceInteractor = voiceInteractor;
            r.activityInfo = info;
            r.compatInfo = compatInfo;
            r.state = state;
            r.persistentState = persistentState;

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

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

            r.profilerInfo = profilerInfo;

            r.overrideConfig = overrideConfig;
            updatePendingConfiguration(curConfig);

            sendMessage(H.LAUNCH_ACTIVITY, r);
        }

具体实现很简单,就是发送一个启动Activity的消息交由Handler处理,交给H处理,这个H具体类的源码:

private class H extends Handler {
        public static final int LAUNCH_ACTIVITY         = 100;
        public static final int PAUSE_ACTIVITY          = 101;
        public static final int PAUSE_ACTIVITY_FINISHING= 102;
        public static final int STOP_ACTIVITY_SHOW      = 103;
        public static final int STOP_ACTIVITY_HIDE      = 104;
        public static final int SHOW_WINDOW             = 105;
        public static final int HIDE_WINDOW             = 106;
        public static final int RESUME_ACTIVITY         = 107;
        public static final int SEND_RESULT             = 108;
        public static final int DESTROY_ACTIVITY        = 109;
        public static final int BIND_APPLICATION        = 110;
        public static final int EXIT_APPLICATION        = 111;
        public static final int NEW_INTENT              = 112;
        public static final int RECEIVER                = 113;
        public static final int CREATE_SERVICE          = 114;
        public static final int SERVICE_ARGS            = 115;
        public static final int STOP_SERVICE            = 116;

        public static final int CONFIGURATION_CHANGED   = 118;
        public static final int CLEAN_UP_CONTEXT        = 119;
        public static final int GC_WHEN_IDLE            = 120;
        public static final int BIND_SERVICE            = 121;
        public static final int UNBIND_SERVICE          = 122;
        public static final int DUMP_SERVICE            = 123;
        public static final int LOW_MEMORY              = 124;
        public static final int ACTIVITY_CONFIGURATION_CHANGED = 125;
        public static final int RELAUNCH_ACTIVITY       = 126;
        public static final int PROFILER_CONTROL        = 127;
        public static final int CREATE_BACKUP_AGENT     = 128;
        public static final int DESTROY_BACKUP_AGENT    = 129;
        public static final int SUICIDE                 = 130;
        public static final int REMOVE_PROVIDER         = 131;
        public static final int ENABLE_JIT              = 132;
        public static final int DISPATCH_PACKAGE_BROADCAST = 133;
        public static final int SCHEDULE_CRASH          = 134;
        public static final int DUMP_HEAP               = 135;
        public static final int DUMP_ACTIVITY           = 136;
        public static final int SLEEPING                = 137;
        public static final int SET_CORE_SETTINGS       = 138;
        public static final int UPDATE_PACKAGE_COMPATIBILITY_INFO = 139;
        public static final int TRIM_MEMORY             = 140;
        public static final int DUMP_PROVIDER           = 141;
        public static final int UNSTABLE_PROVIDER_DIED  = 142;
        public static final int REQUEST_ASSIST_CONTEXT_EXTRAS = 143;
        public static final int TRANSLUCENT_CONVERSION_COMPLETE = 144;
        public static final int INSTALL_PROVIDER        = 145;
        public static final int ON_NEW_ACTIVITY_OPTIONS = 146;
        public static final int CANCEL_VISIBLE_BEHIND = 147;
        public static final int BACKGROUND_VISIBLE_BEHIND_CHANGED = 148;
        public static final int ENTER_ANIMATION_COMPLETE = 149;
        public static final int START_BINDER_TRACKING = 150;
        public static final int STOP_BINDER_TRACKING_AND_DUMP = 151;
        public static final int MULTI_WINDOW_MODE_CHANGED = 152;
        public static final int PICTURE_IN_PICTURE_MODE_CHANGED = 153;
        public static final int LOCAL_VOICE_INTERACTION_STARTED = 154;

        String codeToString(int code) {
            if (DEBUG_MESSAGES) {
                switch (code) {
                    case LAUNCH_ACTIVITY: return "LAUNCH_ACTIVITY";
                    case PAUSE_ACTIVITY: return "PAUSE_ACTIVITY";
                    case PAUSE_ACTIVITY_FINISHING: return "PAUSE_ACTIVITY_FINISHING";
                    case STOP_ACTIVITY_SHOW: return "STOP_ACTIVITY_SHOW";
                    case STOP_ACTIVITY_HIDE: return "STOP_ACTIVITY_HIDE";
                    case SHOW_WINDOW: return "SHOW_WINDOW";
                    case HIDE_WINDOW: return "HIDE_WINDOW";
                    case RESUME_ACTIVITY: return "RESUME_ACTIVITY";
                    case SEND_RESULT: return "SEND_RESULT";
                    case DESTROY_ACTIVITY: return "DESTROY_ACTIVITY";
                    case BIND_APPLICATION: return "BIND_APPLICATION";
                    case EXIT_APPLICATION: return "EXIT_APPLICATION";
                    case NEW_INTENT: return "NEW_INTENT";
                    case RECEIVER: return "RECEIVER";
                    case CREATE_SERVICE: return "CREATE_SERVICE";
                    case SERVICE_ARGS: return "SERVICE_ARGS";
                    case STOP_SERVICE: return "STOP_SERVICE";
                    case CONFIGURATION_CHANGED: return "CONFIGURATION_CHANGED";
                    case CLEAN_UP_CONTEXT: return "CLEAN_UP_CONTEXT";
                    case GC_WHEN_IDLE: return "GC_WHEN_IDLE";
                    case BIND_SERVICE: return "BIND_SERVICE";
                    case UNBIND_SERVICE: return "UNBIND_SERVICE";
                    case DUMP_SERVICE: return "DUMP_SERVICE";
                    case LOW_MEMORY: return "LOW_MEMORY";
                    case ACTIVITY_CONFIGURATION_CHANGED: return "ACTIVITY_CONFIGURATION_CHANGED";
                    case RELAUNCH_ACTIVITY: return "RELAUNCH_ACTIVITY";
                    case PROFILER_CONTROL: return "PROFILER_CONTROL";
                    case CREATE_BACKUP_AGENT: return "CREATE_BACKUP_AGENT";
                    case DESTROY_BACKUP_AGENT: return "DESTROY_BACKUP_AGENT";
                    case SUICIDE: return "SUICIDE";
                    case REMOVE_PROVIDER: return "REMOVE_PROVIDER";
                    case ENABLE_JIT: return "ENABLE_JIT";
                    case DISPATCH_PACKAGE_BROADCAST: return "DISPATCH_PACKAGE_BROADCAST";
                    case SCHEDULE_CRASH: return "SCHEDULE_CRASH";
                    case DUMP_HEAP: return "DUMP_HEAP";
                    case DUMP_ACTIVITY: return "DUMP_ACTIVITY";
                    case SLEEPING: return "SLEEPING";
                    case SET_CORE_SETTINGS: return "SET_CORE_SETTINGS";
                    case UPDATE_PACKAGE_COMPATIBILITY_INFO: return "UPDATE_PACKAGE_COMPATIBILITY_INFO";
                    case TRIM_MEMORY: return "TRIM_MEMORY";
                    case DUMP_PROVIDER: return "DUMP_PROVIDER";
                    case UNSTABLE_PROVIDER_DIED: return "UNSTABLE_PROVIDER_DIED";
                    case REQUEST_ASSIST_CONTEXT_EXTRAS: return "REQUEST_ASSIST_CONTEXT_EXTRAS";
                    case TRANSLUCENT_CONVERSION_COMPLETE: return "TRANSLUCENT_CONVERSION_COMPLETE";
                    case INSTALL_PROVIDER: return "INSTALL_PROVIDER";
                    case ON_NEW_ACTIVITY_OPTIONS: return "ON_NEW_ACTIVITY_OPTIONS";
                    case CANCEL_VISIBLE_BEHIND: return "CANCEL_VISIBLE_BEHIND";
                    case BACKGROUND_VISIBLE_BEHIND_CHANGED: return "BACKGROUND_VISIBLE_BEHIND_CHANGED";
                    case ENTER_ANIMATION_COMPLETE: return "ENTER_ANIMATION_COMPLETE";
                    case MULTI_WINDOW_MODE_CHANGED: return "MULTI_WINDOW_MODE_CHANGED";
                    case PICTURE_IN_PICTURE_MODE_CHANGED: return "PICTURE_IN_PICTURE_MODE_CHANGED";
                    case LOCAL_VOICE_INTERACTION_STARTED: return "LOCAL_VOICE_INTERACTION_STARTED";
                }
            }
            return Integer.toString(code);
        }
        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;
                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");
                    SomeArgs args = (SomeArgs) msg.obj;
                    handlePauseActivity((IBinder) args.arg1, false,
                            (args.argi1 & USER_LEAVING) != 0, args.argi2,
                            (args.argi1 & DONT_REPORT) != 0, args.argi3);
                    maybeSnapshot();
                    Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
                } break;
                case PAUSE_ACTIVITY_FINISHING: {
                    Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityPause");
                    SomeArgs args = (SomeArgs) msg.obj;
                    handlePauseActivity((IBinder) args.arg1, true, (args.argi1 & USER_LEAVING) != 0,
                            args.argi2, (args.argi1 & DONT_REPORT) != 0, args.argi3);
                    Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
                } break;
                case STOP_ACTIVITY_SHOW: {
                    Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityStop");
                    SomeArgs args = (SomeArgs) msg.obj;
                    handleStopActivity((IBinder) args.arg1, true, args.argi2, args.argi3);
                    Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
                } break;
                case STOP_ACTIVITY_HIDE: {
                    Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityStop");
                    SomeArgs args = (SomeArgs) msg.obj;
                    handleStopActivity((IBinder) args.arg1, false, args.argi2, args.argi3);
                    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");
                    SomeArgs args = (SomeArgs) msg.obj;
                    handleResumeActivity((IBinder) args.arg1, true, args.argi1 != 0, true,
                            args.argi3, "RESUME_ACTIVITY");
                    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: " + String.valueOf(msg.obj)));
                    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: " + String.valueOf(msg.obj)));
                    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 CONFIGURATION_CHANGED:
                    Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "configChanged");
                    mCurDefaultDisplayDpi = ((Configuration)msg.obj).densityDpi;
                    mUpdatingSystemConfig = true;
                    handleConfigurationChanged((Configuration)msg.obj, null);
                    mUpdatingSystemConfig = false;
                    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((ActivityConfigChangeData) msg.obj,
                            msg.arg1 == 1 ? REPORT_TO_ACTIVITY : !REPORT_TO_ACTIVITY);
                    Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
                    break;
                case PROFILER_CONTROL:
                    handleProfilerControl(msg.arg1 != 0, (ProfilerInfo)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_ASSIST_CONTEXT_EXTRAS:
                    handleRequestAssistContextExtras((RequestAssistContextExtras)msg.obj);
                    break;
                case TRANSLUCENT_CONVERSION_COMPLETE:
                    handleTranslucentConversionComplete((IBinder)msg.obj, msg.arg1 == 1);
                    break;
                case INSTALL_PROVIDER:
                    handleInstallProvider((ProviderInfo) msg.obj);
                    break;
                case ON_NEW_ACTIVITY_OPTIONS:
                    Pair<IBinder, ActivityOptions> pair = (Pair<IBinder, ActivityOptions>) msg.obj;
                    onNewActivityOptions(pair.first, pair.second);
                    break;
                case CANCEL_VISIBLE_BEHIND:
                    handleCancelVisibleBehind((IBinder) msg.obj);
                    break;
                case BACKGROUND_VISIBLE_BEHIND_CHANGED:
                    handleOnBackgroundVisibleBehindChanged((IBinder) msg.obj, msg.arg1 > 0);
                    break;
                case ENTER_ANIMATION_COMPLETE:
                    handleEnterAnimationComplete((IBinder) msg.obj);
                    break;
                case START_BINDER_TRACKING:
                    handleStartBinderTracking();
                    break;
                case STOP_BINDER_TRACKING_AND_DUMP:
                    handleStopBinderTrackingAndDump((ParcelFileDescriptor) msg.obj);
                    break;
                case MULTI_WINDOW_MODE_CHANGED:
                    handleMultiWindowModeChanged((IBinder) msg.obj, msg.arg1 == 1);
                    break;
                case PICTURE_IN_PICTURE_MODE_CHANGED:
                    handlePictureInPictureModeChanged((IBinder) msg.obj, msg.arg1 == 1);
                    break;
                case LOCAL_VOICE_INTERACTION_STARTED:
                    handleLocalVoiceInteractionStarted((IBinder) ((SomeArgs) msg.obj).arg1,
                            (IVoiceInteractor) ((SomeArgs) msg.obj).arg2);
                    break;
            }
            Object obj = msg.obj;
            if (obj instanceof SomeArgs) {
                ((SomeArgs) obj).recycle();
            }
            if (DEBUG_MESSAGES) Slog.v(TAG, "<<< done: " + codeToString(msg.what));
        }

        private void maybeSnapshot() {
            if (mBoundApplication != null && SamplingProfilerIntegration.isEnabled()) {
                // convert the *private* ActivityThread.PackageInfo to *public* known
                // android.content.pm.PackageInfo
                String packageName = mBoundApplication.info.mPackageName;
                android.content.pm.PackageInfo packageInfo = null;
                try {
                    Context context = getSystemContext();
                    if(context == null) {
                        Log.e(TAG, "cannot get a valid context");
                        return;
                    }
                    PackageManager pm = context.getPackageManager();
                    if(pm == null) {
                        Log.e(TAG, "cannot get a valid PackageManager");
                        return;
                    }
                    packageInfo = pm.getPackageInfo(
                            packageName, PackageManager.GET_ACTIVITIES);
                } catch (NameNotFoundException e) {
                    Log.e(TAG, "cannot get package info for " + packageName, e);
                }
                SamplingProfilerIntegration.writeSnapshot(mBoundApplication.processName, packageInfo);
            }
        }
    }

在LAUNCH_ACTIVITY中,可以看到这么一句handleLaunchActivity(r, null, "LAUNCH_ACTIVITY"),最终是交由handleLaunchActivity方法实现,它的源码是:

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

        if (r.profilerInfo != null) {
            mProfiler.setProfiler(r.profilerInfo);
            mProfiler.startProfiling();
        }

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

        if (localLOGV) Slog.v(
            TAG, "Handling launch of " + r);

        // Initialize before creating the activity
        WindowManagerGlobal.initialize();

        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);

            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.
                performPauseActivityIfNeeded(r, reason);

                // 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;
                }
            }
        } 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();
            }
        }
    }

进而performLaunchActivity方法最终完成了Activity对象的创建和启动过程,并且ActivityThread通过handleResumeActivity方法来调用被启动Activity的onResume这一生命周期方法。

那么performLaunchActivity方法主要完成如下几件事:

  • 从ActivityClientRecord中获取启动的Activity的组件信息
  • 通过Instrumentation的newActivity方法使用类加载器创建Activity对象
  • 通过LoadedApk的makeApplication方法来尝试创建Application对象。值得注意的是在makeApplication方法中如果Application已经被创建过了,那么就不会再重复创建了,这也意味着一个应用只有一个Application对象。同时,Application创建完毕后,系统会调用Application的onCreate方法。
  • 创建ContextImpl对象并通过Activity的attach方法来完成一些重要数据的初始化
  • 调用Activity的onCreate方法

源码如下:

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();
            activity = mInstrumentation.newActivity(
                    cl, component.getClassName(), r.intent);
            StrictMode.incrementExpectedActivityCount(activity.getClass());
            r.intent.setExtrasClassLoader(cl);
            r.intent.prepareToEnterProcess();
            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 {
            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) {
                Context appContext = createBaseContextForActivity(r, activity);
                CharSequence title = r.activityInfo.loadLabel(appContext.getPackageManager());
                Configuration config = new Configuration(mCompatConfiguration);
                if (r.overrideConfig != null) {
                    config.updateFrom(r.overrideConfig);
                }
                if (DEBUG_CONFIGURATION) Slog.v(TAG, "Launching activity "
                        + r.activityInfo.name + " with config " + config);
                Window window = null;
                if (r.mPendingRemoveWindow != null && r.mPreserveWindow) {
                    window = r.mPendingRemoveWindow;
                    r.mPendingRemoveWindow = null;
                    r.mPendingRemoveWindowManager = null;
                }
                activity.attach(appContext, this, getInstrumentation(), r.token,
                        r.ident, app, r.intent, r.activityInfo, title, r.parent,
                        r.embeddedID, r.lastNonConfigurationInstances, config,
                        r.referrer, r.voiceInteractor, window);

                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;
                if (r.isPersistable()) {
                    mInstrumentation.callActivityOnCreate(activity, r.state, r.persistentState);
                } else {
                    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;
                if (!r.activity.mFinished) {
                    activity.performStart();
                    r.stopped = false;
                }
                if (!r.activity.mFinished) {
                    if (r.isPersistable()) {
                        if (r.state != null || r.persistentState != null) {
                            mInstrumentation.callActivityOnRestoreInstanceState(activity, r.state,
                                    r.persistentState);
                        }
                    } else if (r.state != null) {
                        mInstrumentation.callActivityOnRestoreInstanceState(activity, r.state);
                    }
                }
                if (!r.activity.mFinished) {
                    activity.mCalled = false;
                    if (r.isPersistable()) {
                        mInstrumentation.callActivityOnPostCreate(activity, r.state,
                                r.persistentState);
                    } else {
                        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;
    }

所以借用一张流程图,总体流程时序:

整体流程图

阅读扩展

源于对掌握的Android开发基础点进行整理,罗列下已经总结的文章,从中可以看到技术积累的过程。
1,Android系统简介
2,ProGuard代码混淆
3,讲讲Handler+Looper+MessageQueue关系
4,Android图片加载库理解
5,谈谈Android运行时权限理解
6,EventBus初理解
7,Android 常见工具类
8,对于Fragment的一些理解
9,Android 四大组件之 " Activity "
10,Android 四大组件之" Service "
11,Android 四大组件之“ BroadcastReceiver "
12,Android 四大组件之" ContentProvider "
13,讲讲 Android 事件拦截机制
14,Android 动画的理解
15,Android 生命周期和启动模式
16,Android IPC 机制
17,View 的事件体系
18,View 的工作原理
19,理解 Window 和 WindowManager
20,Activity 启动过程分析
21,Service 启动过程分析
22,Android 性能优化
23,Android 消息机制
24,Android Bitmap相关
25,Android 线程和线程池
26,Android 中的 Drawable 和动画
27,RecylerView 中的装饰者模式
28,Android 触摸事件机制
29,Android 事件机制应用
30,Cordova 框架的一些理解
31,有关 Android 插件化思考
32,开发人员必备技能——单元测试

posted @ 2017-02-09 15:50 cryAllen 阅读(...) 评论(...) 编辑 收藏