源码分析之App启动源码分析

想必大家都知道Java程序在启动的时候，最开始加载的函数是main函数

public static void main(String [] args){
        
    }

那么我们Android应用程序是基于Java虚拟机进行开发的，自然入口函数也是main函数，可是平时我们在写Android应用程序并没有看到这个东西啊。那么接下来我们从main函数看起，在桌面点击了App那一刻到底发生了什么。首先来到ActivityThread下，main函数就在这里。

 public static void main(String[] args) {
        Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "ActivityThreadMain");
       //省略部分代码   这里调用了Looper.prepare，解释了我们在主线程可以直接通过Handler去取消息，而在子线程需要手动初始化Looper
        Looper.prepareMainLooper();

        ActivityThread thread = new ActivityThread();
//主要代码是这行，绑定了ActivityThread
        thread.attach(false);

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

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

        // End of event ActivityThreadMain.
        Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
        Looper.loop();

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

这里主要就是对ActivityThread进行绑定，那我们继续

 private void attach(boolean system) {
        sCurrentActivityThread = this;
        mSystemThread = system;
      //省略部分源码
            RuntimeInit.setApplicationObject(mAppThread.asBinder());
            final IActivityManager mgr = ActivityManagerNative.getDefault();
            try {
                mgr.attachApplication(mAppThread);
            } catch (RemoteException ex) {
                // Ignore
            }

可以看到绑定了Application，不过这个ActivityManagerNative.getDefault()是个什么还需要仔细考量。

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;
        }
    };

我们可以看到ActivityManagerNative.getDefault()拿到的是一个标准的单例
，那我们继续看下去，这里通过ServiceManager.getService("activity")，我们来到了ActivityManagerService这个类下，找到如何添加

 public void setSystemProcess() {
        try {
            ServiceManager.addService(Context.ACTIVITY_SERVICE, this, true);
            ServiceManager.addService(ProcessStats.SERVICE_NAME, mProcessStats);
            ServiceManager.addService("meminfo", new MemBinder(this));
            ServiceManager.addService("gfxinfo", new GraphicsBinder(this));
            ServiceManager.addService("dbinfo", new DbBinder(this));

我们点开Context.ACTIVITY_SERVICE = “activity”，这不就是我们要找的吗，这里传递了一个this进去，这个this指向的是当前的ActivityManagerService，那么我们在ActivityThread最开始看到的就是调用的ActivityManagerService的attachApplication，总算找到码头了。

final IActivityManager mgr = ActivityManagerNative.getDefault();
            try {
                mgr.attachApplication(mAppThread);

private final boolean attachApplicationLocked(IApplicationThread thread,
            int pid) {
//省略部分源码，太长了，还是看重要的方法为妙，容易懵逼
 ProfilerInfo profilerInfo = profileFile == null ? null
                    : new ProfilerInfo(profileFile, profileFd, samplingInterval, profileAutoStop);
            thread.bindApplication(processName, appInfo, providers, app.instrumentationClass,
                    profilerInfo, app.instrumentationArguments, app.instrumentationWatcher,
                    app.instrumentationUiAutomationConnection, testMode, enableOpenGlTrace,
                    isRestrictedBackupMode || !normalMode, app.persistent,
                    new Configuration(mConfiguration), app.compat,
                    getCommonServicesLocked(app.isolated),
                    mCoreSettingsObserver.getCoreSettingsLocked());
            updateLruProcessLocked(app, false, null);
            app.lastRequestedGc = app.lastLowMemory = SystemClock.uptimeMillis();
}

这里看到我们又回到了ActivityThread里面。

public final void bindApplication(String processName, ApplicationInfo appInfo,
                List<ProviderInfo> providers, ComponentName instrumentationName,
                ProfilerInfo profilerInfo, Bundle instrumentationArgs,
                IInstrumentationWatcher instrumentationWatcher,
                IUiAutomationConnection instrumentationUiConnection, int debugMode,
                boolean enableOpenGlTrace, boolean isRestrictedBackupMode, boolean persistent,
                Configuration config, CompatibilityInfo compatInfo, Map<String, IBinder> services,
                Bundle coreSettings) {

            if (services != null) {
                // Setup the service cache in the ServiceManager
                ServiceManager.initServiceCache(services);
            }

            setCoreSettings(coreSettings);
            IPackageManager pm = getPackageManager();
            android.content.pm.PackageInfo pi = null;
            try {
                pi = pm.getPackageInfo(appInfo.packageName, 0, UserHandle.myUserId());
            } catch (RemoteException e) {
            }
            if (pi != null) {
                boolean sharedUserIdSet = (pi.sharedUserId != null);
                boolean processNameNotDefault =
                (pi.applicationInfo != null &&
                 !appInfo.packageName.equals(pi.applicationInfo.processName));
                boolean sharable = (sharedUserIdSet || processNameNotDefault);

                // Tell the VMRuntime about the application, unless it is shared
                // inside a process.
                if (!sharable) {
                    VMRuntime.registerAppInfo(appInfo.packageName, appInfo.dataDir,
                                            appInfo.processName);
                }
            }

            AppBindData data = new AppBindData();
            data.processName = processName;
            data.appInfo = appInfo;
            data.providers = providers;
            data.instrumentationName = instrumentationName;
            data.instrumentationArgs = instrumentationArgs;
            data.instrumentationWatcher = instrumentationWatcher;
            data.instrumentationUiAutomationConnection = instrumentationUiConnection;
            data.debugMode = debugMode;
            data.enableOpenGlTrace = enableOpenGlTrace;
            data.restrictedBackupMode = isRestrictedBackupMode;
            data.persistent = persistent;
            data.config = config;
            data.compatInfo = compatInfo;
            data.initProfilerInfo = profilerInfo;
            sendMessage(H.BIND_APPLICATION, data);
        }

也只是初始化了ServiceManager，通过Handler去发送了一个消息。 那我们是走错码头了吗，那还是继续回到ActivityManagerService的attachApplicationLocked

 if (normalMode) {
            try {
//注意，在这里把我们的app传进去了
                if (mStackSupervisor.attachApplicationLocked(app)) {
                    didSomething = true;
                }
            } catch (Exception e) {
                Slog.wtf(TAG, "Exception thrown launching activities in " + app, e);
                badApp = true;
            }
        }

boolean attachApplicationLocked(ProcessRecord app) throws RemoteException {
        final String processName = app.processName;
        boolean didSomething = false;
        for (int displayNdx = mActivityDisplays.size() - 1; displayNdx >= 0; --displayNdx) {
            ArrayList<ActivityStack> stacks = mActivityDisplays.valueAt(displayNdx).mStacks;
            for (int stackNdx = stacks.size() - 1; stackNdx >= 0; --stackNdx) {
                final ActivityStack stack = stacks.get(stackNdx);
                if (!isFrontStack(stack)) {
                    continue;
                }
                ActivityRecord hr = stack.topRunningActivityLocked(null);
                if (hr != null) {
                    if (hr.app == null && app.uid == hr.info.applicationInfo.uid
                            && processName.equals(hr.processName)) {
                        try {
        //这里就是 真的要去启动Activity了！！！
                            if (realStartActivityLocked(hr, app, true, true)) {
                                didSomething = true;
                            }
                        } catch (RemoteException e) {
                            Slog.w(TAG, "Exception in new application when starting activity "
                                  + hr.intent.getComponent().flattenToShortString(), e);
                            throw e;
                        }
                    }
                }
            }
        }
        if (!didSomething) {
            ensureActivitiesVisibleLocked(null, 0);
        }
        return didSomething;
    }

千辛万苦，终于要即将开始启动我们的Activity了，哈哈哈。

final boolean realStartActivityLocked(ActivityRecord r,
            ProcessRecord app, boolean andResume, boolean checkConfig)
            throws RemoteException {
//在这里做了一些判断，判断当前是否是resume状态回来的
 if (andResume) {
                app.hasShownUi = true;
                app.pendingUiClean = true;
            }
            app.forceProcessStateUpTo(mService.mTopProcessState);
            app.thread.scheduleLaunchActivity(new Intent(r.intent), r.appToken,
                    System.identityHashCode(r), r.info, new Configuration(mService.mConfiguration),
                    new Configuration(stack.mOverrideConfig), r.compat, r.launchedFromPackage,
                    task.voiceInteractor, app.repProcState, r.icicle, r.persistentState, results,
                    newIntents, !andResume, mService.isNextTransitionForward(), profilerInfo);
}

 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);
        }

可以看到验证了我们客户端Activity的一些信息之后，还是通过Handler发送消息来启动我们的Activity。

 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);
                    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&1) != 0, msg.arg2,
                            (msg.arg1&2) != 0);
                    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&1) != 0, msg.arg2,
                            (msg.arg1&1) != 0);
                    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;

在这里看到我们activity的生命周期都在这里。看来方向没有错啊，赶紧捧起了我的咖啡继续干起来。我们这边就从StartActiviy这个看吧。

private void handleLaunchActivity(ActivityClientRecord r, Intent customIntent) {
    
        // Initialize before creating the activity
        WindowManagerGlobal.initialize();

        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);

            if (!r.activity.mFinished && r.startsNotResumed) {
                // The activity manager actually wants this one to start out
                // paused, because it needs to be visible but isn't in the
                // foreground.  We accomplish this by going through the
                // normal startup (because activities expect to go through
                // onResume() the first time they run, before their window
                // is displayed), and then pausing it.  However, in this case
                // we do -not- need to do the full pause cycle (of freezing
                // and such) because the activity manager assumes it can just
                // retain the current state it has.
                try {
                    r.activity.mCalled = false;
                    mInstrumentation.callActivityOnPause(r.activity);
                   
                    if (r.isPreHoneycomb()) {
                        r.state = oldState;
                    }
                    if (!r.activity.mCalled) {
                        throw new SuperNotCalledException(
                            "Activity " + r.intent.getComponent().toShortString() +
                            " did not call through to super.onPause()");
                    }

                } catch (SuperNotCalledException e) {
                    throw e;

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

我们可以看到Activity a = performLaunchActivity(r, customIntent);
哇，我们的Activity来了，那我们在平时都是new Activity，这里到底怎么拿到Activity的呢。？

private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {
//验证Activity的信息，Intent，最后通过反射拿到Activity的实例、
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);
            }
        }
}

顿觉索然无味，其实源码也是反射来拿到这个Activity。
到这里，我们的Activity实例已经拿到了，那么Activity的生命还没看到调用啊，onCreate，onStart呢？那我们继续在这里方法看下去，可以看到这样的代码。

  activity.mCalled = false;
                if (r.isPersistable()) {
                    mInstrumentation.callActivityOnCreate(activity, r.state, r.persistentState);
                } else {
                    mInstrumentation.callActivityOnCreate(activity, r.state);
                }

嗯，对，callActivityOnCreate！！！从单词都知道这是调用onCreate()了。hhh~~

 public void callActivityOnCreate(Activity activity, Bundle icicle,
            PersistableBundle persistentState) {
        prePerformCreate(activity);
        activity.performCreate(icicle, persistentState);
        postPerformCreate(activity);
    }

activity.performCreate(icicle, persistentState);那么我们只要到Activity下搜索一下这个方法就可以看到onCreate（）的调用啦~~

文章基于Android源码7.0，也许大家看的源码各不相同，本质缺大同小异，个人理解如有差错，欢迎评论指出。