1、注册观察者

--> PhoneFactory.makeDefaultPhones() 
--> TelephonyComponentFactory.makeSubscriptionInfoUpdater() 
--> new SubscriptionInfoUpdater() 
--> PhoneConfigurationManager.registerForMultiSimConfigChange(this, EVENT_MULTI_SIM_CONFIG_CHANGED, null)
--> sMultiSimConfigChangeRegistrants.addUnique(h, what, obj)    观察者注册到通知者中

到这步，注册了对 EVENT_MULTI_SIM_CONFIG_CHANGED 事件的观察，当收到通知者notify时，就由SubscriptionInfoUpdater这个Handler对象来处理事件。

其实只要某个类中调用了PhoneConfigurationManager.registerForMultiSimConfigChange()，就会产生一个观察者并注册到通知者中
比如下面这些类的方法中都有注册观察者

2、触发事件

--> PhoneInterfaceManager.switchMultiSimConfig() 
--> RadioConfig.setNumOfLiveModems()
--> RadioConfigProxy.setNumOfLiveModems()  
--> 下发modem请求
--> modem返回响应，回调处理事件 EVENT_SWITCH_DSDS_CONFIG_DONE
--> ConfigurationManagerHandler.handleMessage()

--> PhoneConfigurationManager.onMultiSimConfigChanged()
--> broadcastMultiSimConfigChange()
--> notifyMultiSimConfigChange()   
--> sMultiSimConfigChangeRegistrants.notifyResult()   1.通知者通知观察者
--> SubscriptionInfoUpdater.handleMessage()
--> onMultiSimConfigChanged()

    private void onMultiSimConfigChanged() {
        int activeModemCount = ((TelephonyManager) sContext.getSystemService(
                Context.TELEPHONY_SERVICE)).getActiveModemCount();
        // For inactive modems, reset its states.
        for (int phoneId = activeModemCount; phoneId < SUPPORTED_MODEM_COUNT; phoneId++) {
            sIccId[phoneId] = null;
            sSimCardState[phoneId] = TelephonyManager.SIM_STATE_UNKNOWN;
            sSimApplicationState[phoneId] = TelephonyManager.SIM_STATE_UNKNOWN;
        }
    }

--> Intent intent = new Intent(ACTION_MULTI_SIM_CONFIG_CHANGED); sendBroadcast(intent)    2.发送广播
--> ConfigLoaderBroadcastReceiver.onReceive()
--> sendMessge(EVENT_MULTI_SIM_CONFIG_CHANGED)
--> ConfigHandler.handleMessage()
--> CarrierConfigLoader.onMultiSimConfigChanged()
--> updateConfigForPhoneId()
--> sendMessage(mHandler.obtainMessage(EVENT_DO_FETCH_DEFAULT, phoneId, -1));
待续。。。