class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        val binding = ActivityMainBinding.inflate(LayoutInflater.from(baseContext))
        setContentView(binding.root)
        //獲取ViewModel實(shí)例
        val viewModel: TextViewModel = ViewModelProvider(this).get(TextViewModel::class.java)
        //訂閱數(shù)據(jù)
        viewModel.liveData.observe(this, { println(it) })
        //調(diào)用函數(shù)
        viewModel.test()
    }
    class TextViewModel : ViewModel() {
        val liveData = MediatorLiveData<String>()
        fun test() {
            liveData.postValue("Hello")
        }
    }
}

    public ViewModelProvider(@NonNull ViewModelStoreOwner owner) {
        this(owner.getViewModelStore(), owner instanceof HasDefaultViewModelProviderFactory
                ? ((HasDefaultViewModelProviderFactory) owner).getDefaultViewModelProviderFactory()
                : NewInstanceFactory.getInstance());
    }
    public ViewModelProvider(@NonNull ViewModelStore store, @NonNull Factory factory) {
        mFactory = factory;
        mViewModelStore = store;
    

    @NonNull
    @MainThread
    public <T extends ViewModel> T get(@NonNull Class<T> modelClass) {
        //獲取類名
        String canonicalName = modelClass.getCanonicalName();
        if (canonicalName == null) {
            throw new IllegalArgumentException("Local and anonymous classes can not be ViewModels");
        }
        return get(DEFAULT_KEY + ":" + canonicalName, modelClass);
    }
    @NonNull
    @MainThread
    public <T extends ViewModel> T get(@NonNull String key, @NonNull Class<T> modelClass) {
        //通過(guò)key到ViewModelStore中取
        ViewModel viewModel = mViewModelStore.get(key);
        
        //如果取到ViewModel 代表已經(jīng)創(chuàng)建過(guò)這個(gè)ViewModel 直接返回
        if (modelClass.isInstance(viewModel)) {
            if (mFactory instanceof OnRequeryFactory) {
                ((OnRequeryFactory) mFactory).onRequery(viewModel);
            }
            return (T) viewModel;
        } else {
            //noinspection StatementWithEmptyBody
            if (viewModel != null) {
                // TODO: log a warning.
            }
        }
        //通過(guò)Factor利用反射創(chuàng)建一個(gè)實(shí)例
        if (mFactory instanceof KeyedFactory) {
            viewModel = ((KeyedFactory) mFactory).create(key, modelClass);
        } else {
            viewModel = mFactory.create(modelClass);
        }
        //把ViewModel實(shí)例存儲(chǔ)到ViewModelStore中
        mViewModelStore.put(key, viewModel);
        return (T) viewModel;
    }

ActivityThread{
    private void handleRelaunchActivityInner(ActivityClientRecord r, int configChanges,
            List<ResultInfo> pendingResults, List<ReferrerIntent> pendingIntents,
            PendingTransactionActions pendingActions, boolean startsNotResumed,
            Configuration overrideConfig, String reason) {
        // Preserve last used intent, it may be set from Activity#setIntent().
        final Intent customIntent = r.activity.mIntent;
        // Need to ensure state is saved.
        if (!r.paused) {
            performPauseActivity(r, false, reason, null /* pendingActions */);
        }
        if (!r.stopped) {
            callActivityOnStop(r, true /* saveState */, reason);
        }
        //銷毀Activity
        handleDestroyActivity(r.token, false, configChanges, true, reason);
        //啟動(dòng)Activity
        handleLaunchActivity(r, pendingActions, customIntent);
    }
}

ActivityThread{
        @Override
    public void handleDestroyActivity(IBinder token, boolean finishing, int configChanges,
            boolean getNonConfigInstance, String reason) {
        //執(zhí)行銷毀Activity
        ActivityClientRecord r = performDestroyActivity(token, finishing,
                configChanges, getNonConfigInstance, reason);
    }
    ActivityClientRecord performDestroyActivity(IBinder token, boolean finishing,
            int configChanges, boolean getNonConfigInstance, String reason) {
        //通過(guò)token獲取Activity的記錄
        ActivityClientRecord r = mActivities.get(token);
        if (r != null) {
            //是否需要獲取配置實(shí)例
            if (getNonConfigInstance) {
                try {
                    //調(diào)用Activity的retainNonConfigurationInstances方法獲取配置實(shí)例
                    r.lastNonConfigurationInstances
                            = r.activity.retainNonConfigurationInstances();
                } catch (Exception e) {
                }
            }
            r.setState(ON_DESTROY);
        }
        //通過(guò)token移除這條Activity的記錄
        synchronized (mResourcesManager) {
            mActivities.remove(token);
        }
        return r;
    }
}

Activity{
    NonConfigurationInstances retainNonConfigurationInstances() {
        //獲取NonConfigurationInstances對(duì)象
        Object activity = onRetainNonConfigurationInstance();
        HashMap<String, Object> children = onRetainNonConfigurationChildInstances();
        FragmentManagerNonConfig fragments = mFragments.retainNestedNonConfig();
        mFragments.doLoaderStart();
        mFragments.doLoaderStop(true);
        ArrayMap<String, LoaderManager> loaders = mFragments.retainLoaderNonConfig();
        //創(chuàng)建NonConfigurationInstances實(shí)例
        NonConfigurationInstances nci = new NonConfigurationInstances();
        nci.activity = activity;
        nci.children = children;
        nci.fragments = fragments;
        nci.loaders = loaders;
        if (mVoiceInteractor != null) {
            mVoiceInteractor.retainInstance();
            nci.voiceInteractor = mVoiceInteractor;
        }
        return nci;
    }
}
ComponentActivity{
    @Override
    @Nullable
    public final Object onRetainNonConfigurationInstance() {
        Object custom = onRetainCustomNonConfigurationInstance();
        //獲取ViewModelStore
        ViewModelStore viewModelStore = mViewModelStore;
        if (viewModelStore == null) {
            // No one called getViewModelStore(), so see if there was an existing
            // ViewModelStore from our last NonConfigurationInstance
            NonConfigurationInstances nc =
                    (NonConfigurationInstances) getLastNonConfigurationInstance();
            if (nc != null) {
                viewModelStore = nc.viewModelStore;
            }
        }
        if (viewModelStore == null && custom == null) {
            return null;
        }
        //創(chuàng)建NonConfigurationInstances實(shí)例
        NonConfigurationInstances nci = new NonConfigurationInstances();
        nci.custom = custom;
        nci.viewModelStore = viewModelStore;
        return nci;
    }
}

ActivityThread{
    private void handleRelaunchActivityInner(ActivityClientRecord r, int configChanges,
            List<ResultInfo> pendingResults, List<ReferrerIntent> pendingIntents,
            PendingTransactionActions pendingActions, boolean startsNotResumed,
            Configuration overrideConfig, String reason) {
        // Preserve last used intent, it may be set from Activity#setIntent().
        final Intent customIntent = r.activity.mIntent;
        // Need to ensure state is saved.
        if (!r.paused) {
            performPauseActivity(r, false, reason, null /* pendingActions */);
        }
        if (!r.stopped) {
            callActivityOnStop(r, true /* saveState */, reason);
        }
        //銷毀Activity
        handleDestroyActivity(r.token, false, configChanges, true, reason);
        //啟動(dòng)Activity
        handleLaunchActivity(r, pendingActions, customIntent);
    }
}

ActivityThread{
    @Override
    public Activity handleLaunchActivity(ActivityClientRecord r,
            PendingTransactionActions pendingActions, Intent customIntent) {
        // Make sure we are running with the most recent config.
        handleConfigurationChanged(null, null);
        //去啟動(dòng)Activity
        final Activity a = performLaunchActivity(r, customIntent);
        return a;
    }
    private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {
        try {
            Application app = r.packageInfo.makeApplication(false, mInstrumentation);
            if (activity != null) {
                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;
                }
                appContext.setOuterContext(activity);
                //調(diào)用當(dāng)前打開的Activity的attach()方法
                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, r.configCallback,
                        r.assistToken);
                r.activity = activity;
            }
            r.setState(ON_CREATE);
            //保存這條Activity記錄
            synchronized (mResourcesManager) {
                mActivities.put(r.token, r);
            }
        } catch (SuperNotCalledException e) {
            throw e;
        } catch (Exception e) {
        }
        return activity;
    }
}

Activity{
     final void attach(Context context, ActivityThread aThread,
            Instrumentation instr, IBinder token, int ident,
            Application application, Intent intent, ActivityInfo info,
            CharSequence title, Activity parent, String id,
            NonConfigurationInstances lastNonConfigurationInstances,
            Configuration config, String referrer, IVoiceInteractor voiceInteractor,
            Window window, ActivityConfigCallback activityConfigCallback, IBinder assistToken) {
        attachBaseContext(context);
        mFragments.attachHost(null /*parent*/);
        //賦值給mLastNonConfigurationInstances
        mLastNonConfigurationInstances = lastNonConfigurationInstances;
        setAutofillOptions(application.getAutofillOptions());
        setContentCaptureOptions(application.getContentCaptureOptions());
    }
    public Object getLastNonConfigurationInstance() {
        return mLastNonConfigurationInstances != null
                ? mLastNonConfigurationInstances.activity : null;
    }
}
ComponentActivity{
    public ViewModelStore getViewModelStore() {
        if (getApplication() == null) {
            throw new IllegalStateException("Your activity is not yet attached to the "
                    + "Application instance. You can't request ViewModel before onCreate call.");
        }
        if (mViewModelStore == null) {
            //先去lastNonConfigurationInstance中取，沒(méi)有再創(chuàng)建
            NonConfigurationInstances nc =
                    (NonConfigurationInstances) getLastNonConfigurationInstance();
            if (nc != null) {
                // Restore the ViewModelStore from NonConfigurationInstances
                mViewModelStore = nc.viewModelStore;
            }
            if (mViewModelStore == null) {
                mViewModelStore = new ViewModelStore();
            }
        }
        return mViewModelStore;
    }
}

ComponentActivity{
    public ComponentActivity(){
        //訂閱生命周期，當(dāng)生命周期==ON_DESTROY，清除ViewModel數(shù)據(jù)
        getLifecycle().addObserver(new LifecycleEventObserver() {
            @Override
            public void onStateChanged(@NonNull LifecycleOwner source,
                    @NonNull Lifecycle.Event event) {
                if (event == Lifecycle.Event.ON_DESTROY) {
                    if (!isChangingConfigurations()) {
                        getViewModelStore().clear();
                    }
                }
            }
        });
    }
}
ViewModelStore{
    public final void clear() {
        //遍歷所有ViewModel并調(diào)用其clear()方法清空數(shù)據(jù)
        for (ViewModel vm : mMap.values()) {
            vm.clear();
        }
        //清空所有ViewModel
        mMap.clear();
    }
}