Android源码之单例设计模式

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 LayoutInflater.from(context).inflate(layout, null, false);

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 public static LayoutInflater from(Context context) {
        LayoutInflater LayoutInflater =
                (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        if (LayoutInflater == null) {
            throw new AssertionError("LayoutInflater not found.");
        }
        return LayoutInflater;
    }

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public abstract class Context {
}

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public static void main(String[] args) {
        Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "ActivityThreadMain");
        SamplingProfilerIntegration.start();

        CloseGuard.setEnabled(false);

        Environment.initForCurrentUser();

        // Set the reporter for event logging in libcore
        EventLogger.setReporter(new EventLoggingReporter());

        // Make sure TrustedCertificateStore looks in the right place for CA certificates
        final File configDir = Environment.getUserConfigDirectory(UserHandle.myUserId());
        TrustedCertificateStore.setDefaultUserDirectory(configDir);

        Process.setArgV0("<pre-initialized>");

        // 创建主线程的Looper对象
        Looper.prepareMainLooper();

        // 创建了一个 ActivityThrad 对象
        ActivityThread thread = new ActivityThread();
        // false 代表不是系统应用
        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);
        // 开启消息循环
        Looper.loop();

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

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 private void attach(boolean system) {
        sCurrentActivityThread = this;
        mSystemThread = system;
        if (!system) {
            ViewRootImpl.addFirstDrawHandler(new Runnable() {
                @Override
                public void run() {
                    ensureJitEnabled();
                }
            });
            android.ddm.DdmHandleAppName.setAppName("<pre-initialized>",
                                                    UserHandle.myUserId());
            RuntimeInit.setApplicationObject(mAppThread.asBinder());
            // 这里是 Binder 机制与  ActivityManagerService 进行通信
            final IActivityManager mgr = ActivityManager.getService();
            try {
                // 关联 application
                mgr.attachApplication(mAppThread);
            } catch (RemoteException ex) {
                throw ex.rethrowFromSystemServer();
            }
            // Watch for getting close to heap limit.
            BinderInternal.addGcWatcher(new Runnable() {
                @Override public void run() {
                    if (!mSomeActivitiesChanged) {
                        return;
                    }
                    Runtime runtime = Runtime.getRuntime();
                    long dalvikMax = runtime.maxMemory();
                    long dalvikUsed = runtime.totalMemory() - runtime.freeMemory();
                    if (dalvikUsed > ((3*dalvikMax)/4)) {
                        if (DEBUG_MEMORY_TRIM) Slog.d(TAG, "Dalvik max=" + (dalvikMax/1024)
                                + " total=" + (runtime.totalMemory()/1024)
                                + " used=" + (dalvikUsed/1024));
                        mSomeActivitiesChanged = false;
                        try {
                            mgr.releaseSomeActivities(mAppThread);
                        } catch (RemoteException e) {
                            throw e.rethrowFromSystemServer();
                        }
                    }
                }
            });
        } else {
            // 这里是 false 不是系统应用的时候不会被调用
        }

    // 代码省略
     
    }

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 private void handleLaunchActivity(ActivityClientRecord r, Intent customIntent, String reason) {
        unscheduleGcIdler();
        mSomeActivitiesChanged = true;

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

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

        // Initialize before creating the activity
        WindowManagerGlobal.initialize();
        
        // 调用了启动了一个 Activity 方法
        Activity a = performLaunchActivity(r, customIntent);

        // 代码省略...
     
    }

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 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);
        }

        // 这里创建了一个 ContextImpl 对象
        ContextImpl appContext = createBaseContextForActivity(r);
        Activity activity = null;
        try {
            // 获取了一个 ClassLoader
            java.lang.ClassLoader cl = appContext.getClassLoader();
            // 反射创建了一个 Activity
            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) {
                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);
                // 将创建好的 context 对象, 传递给 Activity
                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);

                if (customIntent != null) {
                    activity.mIntent = customIntent;
                }
                r.lastNonConfigurationInstances = null;
                checkAndBlockForNetworkAccess();
                activity.mStartedActivity = false;
                int theme = r.activityInfo.getThemeResource();
                if (theme != 0) {
                    activity.setTheme(theme);
                }

                activity.mCalled = false;
                if (r.isPersistable()) {
                   // 调用Activity 的 onCreate 方法 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;
    }

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class ContextImpl extends Context { 
    
    @Override
    public String getSystemServiceName(Class<?> serviceClass) {
        return SystemServiceRegistry.getSystemServiceName(serviceClass);
    }
    
}

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final class SystemServiceRegistry {

    // 系统的很多服务都存在了这个集合当中了
    private static final HashMap<Class<?>, String> SYSTEM_SERVICE_NAMES =
            new HashMap<Class<?>, String>();
            

    // Not instantiable.
    private SystemServiceRegistry() { }

    // 静态代码块的实现,第一次加载类的时候就会被执行
    static {
        // LAYOUT_INFLATER_SERVICE 的服务 就在这个时候就已经 注册了
        registerService(Context.LAYOUT_INFLATER_SERVICE, LayoutInflater.class,
                new CachedServiceFetcher<LayoutInflater>() {
            @Override
            public LayoutInflater createService(ContextImpl ctx) {
                // 真正的具体的实现类可以发现是 PhoneLayoutInflater
                return new PhoneLayoutInflater(ctx.getOuterContext());
            }});
            
            // 软键盘的一个服务
             registerService(Context.INPUT_METHOD_SERVICE, InputMethodManager.class,
                new StaticServiceFetcher<InputMethodManager>() {
            @Override
            public InputMethodManager createService() {
                return InputMethodManager.getInstance();
            }});
            
            // 电量的一个服务
            registerService(Context.BATTERY_SERVICE, BatteryManager.class,
                new StaticServiceFetcher<BatteryManager>() {
            @Override
            public BatteryManager createService() throws ServiceNotFoundException {
                IBatteryStats stats = IBatteryStats.Stub.asInterface(
                        ServiceManager.getServiceOrThrow(BatteryStats.SERVICE_NAME));
                IBatteryPropertiesRegistrar registrar = IBatteryPropertiesRegistrar.Stub
                        .asInterface(ServiceManager.getServiceOrThrow("batteryproperties"));
                return new BatteryManager(stats, registrar);
            }});

            
            //网络的一个服务
            registerService(Context.NETWORK_POLICY_SERVICE, NetworkPolicyManager.class,
                new CachedServiceFetcher<NetworkPolicyManager>() {
            @Override
            public NetworkPolicyManager createService(ContextImpl ctx) throws ServiceNotFoundException {
                return new NetworkPolicyManager(ctx, INetworkPolicyManager.Stub.asInterface(
                        ServiceManager.getServiceOrThrow(Context.NETWORK_POLICY_SERVICE)));
            }});

        // 通知的一个服务
        registerService(Context.NOTIFICATION_SERVICE, NotificationManager.class,
                new CachedServiceFetcher<NotificationManager>() {
            @Override
            public NotificationManager createService(ContextImpl ctx) {
                final Context outerContext = ctx.getOuterContext();
                return new NotificationManager(
                    new ContextThemeWrapper(outerContext,
                            Resources.selectSystemTheme(0,
                                    outerContext.getApplicationInfo().targetSdkVersion,
                                    com.android.internal.R.style.Theme_Dialog,
                                    com.android.internal.R.style.Theme_Holo_Dialog,
                                    com.android.internal.R.style.Theme_DeviceDefault_Dialog,
                                    com.android.internal.R.style.Theme_DeviceDefault_Light_Dialog)),
                    ctx.mMainThread.getHandler());
            }});

    }
          

    
    /**
     * Gets a system service from a given context.
     */
    public static Object getSystemService(ContextImpl ctx, String name) {
        // 获取系统服务的时候, 就会从这个集合中去拿
        ServiceFetcher<?> fetcher = SYSTEM_SERVICE_FETCHERS.get(name);
        return fetcher != null ? fetcher.getService(ctx) : null;
    }  
      
        /**
     * Gets the name of the system-level service that is represented by the specified class.
     */
    public static String getSystemServiceName(Class<?> serviceClass) {
        return SYSTEM_SERVICE_NAMES.get(serviceClass);
    }
      

}

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public class PhoneLayoutInflater extends LayoutInflater {
    // 关键部分, 定义了一些 系统view 的前缀
    private static final String[] sClassPrefixList = {
        "android.widget.",
        "android.webkit.",
        "android.app."
    };

    /**
     * Instead of instantiating directly, you should retrieve an instance
     * through {@link Context#getSystemService}
     *
     * @param context The Context in which in which to find resources and other
     *                application-specific things.
     *
     * @see Context#getSystemService
     */
    public PhoneLayoutInflater(Context context) {
        super(context);
    }

    protected PhoneLayoutInflater(LayoutInflater original, Context newContext) {
        super(original, newContext);
    }

    /** Override onCreateView to instantiate names that correspond to the
        widgets known to the Widget factory. If we don't find a match,
        call through to our super class.
    */
    @Override protected View onCreateView(String name, AttributeSet attrs) throws ClassNotFoundException {
        // 在 View 的名字的前面添加前缀,构造一个View的完整路径, 比如android.widget.TextView
        for (String prefix : sClassPrefixList) {
            try {
                View view = createView(name, prefix, attrs);
                if (view != null) {
                    return view;
                }
            } catch (ClassNotFoundException e) {
                // In this case we want to let the base class take a crack
                // at it.
            }
        }

        return super.onCreateView(name, attrs);
    }

    public LayoutInflater cloneInContext(Context newContext) {
        return new PhoneLayoutInflater(this, newContext);
    }
}