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本篇內(nèi)容主要講解“Android NTP時間同步機制實例分析”,感興趣的朋友不妨來看看。本文介紹的方法操作簡單快捷,實用性強。下面就讓小編來帶大家學(xué)習(xí)“Android NTP時間同步機制實例分析”吧!
NTP是Android原生通過網(wǎng)絡(luò)獲取時間的機制,其中關(guān)鍵代碼邏輯都在NetworkTimeUpdateService,它是Android系統(tǒng)服務(wù),由SystemServer啟動。
我們從它的構(gòu)造方法開始分析:
public NetworkTimeUpdateService(Context context) { mContext = context; //NtpTrustedTime用于獲取網(wǎng)絡(luò)時間 mTime = NtpTrustedTime.getInstance(context); mAlarmManager = mContext.getSystemService(AlarmManager.class); mTimeDetector = mContext.getSystemService(TimeDetector.class); mCM = mContext.getSystemService(ConnectivityManager.class); Intent pollIntent = new Intent(ACTION_POLL, null); //創(chuàng)建mPendingPollIntent,用于發(fā)送定時廣播 mPendingPollIntent = PendingIntent.getBroadcast(mContext, POLL_REQUEST, pollIntent, 0); // 請求服務(wù)器頻率 86400000ms = 24h //從配置文件LINUX/android/frameworks/base/core/res/res/values/config.xml中解析獲得 mPollingIntervalMs = mContext.getResources().getInteger( com.android.internal.R.integer.config_ntpPollingInterval); //請求時間間隔 60000ms = 10min mPollingIntervalShorterMs = mContext.getResources().getInteger( com.android.internal.R.integer.config_ntpPollingIntervalShorter); //最大嘗試次數(shù) 3 mTryAgainTimesMax = mContext.getResources().getInteger( com.android.internal.R.integer.config_ntpRetry); mWakeLock = context.getSystemService(PowerManager.class).newWakeLock( PowerManager.PARTIAL_WAKE_LOCK, TAG); }
構(gòu)造方法中主要是對各種變量進行初始化操作,接下來分析systemRunning方法,它是個public方法,NetworkTimeUpdateService創(chuàng)建時,被SystemServer調(diào)用。
/** Initialize the receivers and initiate the first NTP request */ public void systemRunning() { //注冊廣播 registerForAlarms(); //初始化Handler HandlerThread thread = new HandlerThread(TAG); thread.start(); mHandler = new MyHandler(thread.getLooper()); //向ConnectivityManager注冊網(wǎng)絡(luò)狀況監(jiān)聽 mNetworkTimeUpdateCallback = new NetworkTimeUpdateCallback(); mCM.registerDefaultNetworkCallback(mNetworkTimeUpdateCallback, mHandler); //使用ContentObsrver監(jiān)聽Settings.Global.AUTO_TIME值的變化 mAutoTimeSettingObserver = new AutoTimeSettingObserver(mContext, mHandler, EVENT_AUTO_TIME_ENABLED); mAutoTimeSettingObserver.observe(); } private void registerForAlarms() { mContext.registerReceiver( new BroadcastReceiver() { @Override public void onReceive(Context context, Intent intent) { mHandler.obtainMessage(EVENT_POLL_NETWORK_TIME).sendToTarget(); } }, new IntentFilter(ACTION_POLL)); }
這個方法中NetworkTimeUpdateService注冊了三個監(jiān)聽:
1.調(diào)用registerForAlarms,注冊一個廣播接收者,接收ACTION_POLL廣播,收到后向消息隊列發(fā)送一個EVENT_POLL_NETWORK_TIME的事件;
2.向ConnectivityManager注冊網(wǎng)絡(luò)狀況監(jiān)聽;
3.監(jiān)聽Settings.Global.AUTO_TIME值的變化。
咱們對這三個監(jiān)聽以及如何觸發(fā)挨個的分析。
mNetworkTimeUpdateCallback = new NetworkTimeUpdateCallback(); mCM.registerDefaultNetworkCallback(mNetworkTimeUpdateCallback, mHandler); private class NetworkTimeUpdateCallback extends NetworkCallback { @Override public void onAvailable(Network network) { Log.d(TAG, String.format("New default network %s; checking time.", network)); mDefaultNetwork = network; // Running on mHandler so invoke directly. onPollNetworkTime(EVENT_NETWORK_CHANGED); } @Override public void onLost(Network network) { if (network.equals(mDefaultNetwork)) mDefaultNetwork = null; } }
NetworkTimeUpdateCallback實現(xiàn)了NetworkCallback接口,當(dāng)被回調(diào)onAvailable(網(wǎng)絡(luò)切換/可用)時, 賦值mDefaultNetwork并調(diào)用onPollNetworkTime(EVENT_NETWORK_CHANGED)方法。
mAutoTimeSettingObserver = new AutoTimeSettingObserver(mContext, mHandler, EVENT_AUTO_TIME_ENABLED); mAutoTimeSettingObserver.observe(); /** * Observer to watch for changes to the AUTO_TIME setting. It only triggers when the setting * is enabled. */ private static class AutoTimeSettingObserver extends ContentObserver { private final Context mContext; private final int mMsg; private final Handler mHandler; AutoTimeSettingObserver(Context context, Handler handler, int msg) {...} void observe() { ContentResolver resolver = mContext.getContentResolver(); resolver.registerContentObserver(Settings.Global.getUriFor(Settings.Global.AUTO_TIME), false, this); } @Override public void onChange(boolean selfChange) { if (isAutomaticTimeEnabled()) { mHandler.obtainMessage(mMsg).sendToTarget(); } } /** * Checks if the user prefers to automatically set the time. */ private boolean isAutomaticTimeEnabled() { ContentResolver resolver = mContext.getContentResolver(); return Settings.Global.getInt(resolver, Settings.Global.AUTO_TIME, 0) != 0; } }
監(jiān)聽Settings.Global.AUTO_TIME的變化,當(dāng)值改變且AUTO_TIME != 0 時,向消息隊列發(fā)送一個類型為EVENT_AUTO_TIME_ENABLED的消息。
看到這有三個東西我們還沒確認(rèn),何時發(fā)送ACTION_POLL廣播、onPollNetworkTime方法實現(xiàn)、Handler的實現(xiàn)。為了更有條理我打亂一下順序,先介紹Handler和onPollNetworkTime。
/** Handler to do the network accesses on */ private class MyHandler extends Handler { MyHandler(Looper l) { super(l); } @Override public void handleMessage(Message msg) { switch (msg.what) { case EVENT_AUTO_TIME_ENABLED: case EVENT_POLL_NETWORK_TIME: case EVENT_NETWORK_CHANGED: onPollNetworkTime(msg.what); break; } } }
三種類型的消息最終都會調(diào)用onPollNetworkTime,只有參數(shù)不一樣。
private void onPollNetworkTime(int event) { // If we don't have any default network, don't bother. if (mDefaultNetwork == null) return; mWakeLock.acquire(); try { onPollNetworkTimeUnderWakeLock(event); } finally { mWakeLock.release(); } }
當(dāng)前無網(wǎng)絡(luò)情況直接返回,并使用PowerManager.WakeLock(屏幕恒亮)調(diào)用onPollNetworkTimeUnderWakeLock(event)。
private void onPollNetworkTimeUnderWakeLock(int event) { // 使用NtpTrustedTime獲取網(wǎng)絡(luò)時間 NtpTrustedTime.TimeResult cachedNtpResult = mTime.getCachedTimeResult(); //cachedNtpResult.getAgeMillis()是上次請求ntp服務(wù)器的時間 //如果大于等于1天,則強制刷新時間 if (cachedNtpResult == null || cachedNtpResult.getAgeMillis() >= mPollingIntervalMs) { if (DBG) Log.d(TAG, "Stale NTP fix; forcing refresh"); //該方法是個阻塞方法 mTime.forceRefresh(); cachedNtpResult = mTime.getCachedTimeResult(); } //cachedNtpResult.getAgeMillis() < 1天 if (cachedNtpResult != null && cachedNtpResult.getAgeMillis() < mPollingIntervalMs) { //設(shè)置定時廣播,1天后觸發(fā) resetAlarm(mPollingIntervalMs); // Suggest the time to the time detector. It may choose use it to set the system clock. // 設(shè)置系統(tǒng)時間 TimestampedValue<Long> timeSignal = new TimestampedValue<>( cachedNtpResult.getElapsedRealtimeMillis(), cachedNtpResult.getTimeMillis()); NetworkTimeSuggestion timeSuggestion = new NetworkTimeSuggestion(timeSignal); timeSuggestion.addDebugInfo("Origin: NetworkTimeUpdateService. event=" + event); mTimeDetector.suggestNetworkTime(timeSuggestion); } else { mTryAgainCounter++; if (mTryAgainTimesMax < 0 || mTryAgainCounter <= mTryAgainTimesMax) { //設(shè)置定時廣播,10分鐘后觸發(fā) resetAlarm(mPollingIntervalShorterMs); } else { //設(shè)置定時廣播,1天后觸發(fā) mTryAgainCounter = 0; resetAlarm(mPollingIntervalMs); } } }
注意到上面調(diào)用了resetAlarm(),該方法即是定時發(fā)送ACTION_POLL廣播。
private void resetAlarm(long interval) { mAlarmManager.cancel(mPendingPollIntent); long now = SystemClock.elapsedRealtime(); long next = now + interval; mAlarmManager.set(AlarmManager.ELAPSED_REALTIME, next, mPendingPollIntent); }
總結(jié)一下onPollNetworkTimeUnderWakeLock做的事情:
到此,相信大家對“Android NTP時間同步機制實例分析”有了更深的了解,不妨來實際操作一番吧!這里是億速云網(wǎng)站,更多相關(guān)內(nèi)容可以進入相關(guān)頻道進行查詢,關(guān)注我們,繼續(xù)學(xué)習(xí)!
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