NITZ - Network Identity andTime Zone，网络标识和时区，是一种用于自动配置本地时间和日期的机制，同时也通过无线网向移动设备提供运营商信息。NITZ经常被用来自动更新移动电话的系统时钟，Android原有的更新机制就是采用NITZ方式，这是一种运营商的可选服务。其基本原理简单的来说，就是UI根据 Modem主动上报的时间信息，更新终端系统的时间及时区。
初始化：构造函数
ServiceStateTracker() {
…
mCi.setOnNITZTime(this, EVENT_NITZ_TIME, null);
…
}
接收到EVENT_NITZ_TIME后，调用 setTimeFromNITZString去设置时间和时区
public void handleMessage(Message msg) {
...
case EVENT_NITZ_TIME:
ar = (AsyncResult) msg.obj;
String nitzString = (String)((Object[])ar.result)[0];
long nitzReceiveTime = ((Long)((Object[])ar.result)[1]).longValue();
setTimeFromNITZString(nitzString, nitzReceiveTime);
break;
...
}
setTimeFromNITZString 负责解析传过来字符串（nitzString）并进行时间和时区的设置
private
void
setTimeFromNITZString
(String nitzString,
long
nitzReceiveTime) {
long
start = SystemClock.elapsedRealtime();
if
(DBG) {
Rlog.d(LOG_TAG, "NITZ: " + nitzString + "," + nitzReceiveTime
+ " start="+ start + " delay="+ (start - nitzReceiveTime));
}
NitzData newNitzData = NitzData.parse(nitzString);
if
(newNitzData !=
null
) {
try
{
TimeStampedValue<NitzData> nitzSignal = new TimeStampedValue<>(newNitzData, nitzReceiveTime);
mNitzState.handleNitzReceived(nitzSignal);
}
finally
{
}
}
NitzStateMachine.java解析nitz时间
@NitzStateMachine.java /**
* Handle a new NITZ signal being received.
*/
public void handleNitzReceived(TimeStampedValue<NitzData> nitzSignal) {
handleTimeZoneFromNitz(nitzSignal);
handleTimeFromNitz(nitzSignal);
} private void handleTimeZoneFromNitz(TimeStampedValue<NitzData> nitzSignal) {String zoneId;
if (newNitzData.getEmulatorHostTimeZone() != null) {
zoneId = newNitzData.getEmulatorHostTimeZone().getID();
} else {
if (!mGotCountryCode) {
zoneId = null;
} else if (!TextUtils.isEmpty(iso)) {
OffsetResult lookupResult =
mTimeZoneLookupHelper.lookupByNitzCountry(newNitzData, iso);
zoneId = lookupResult != null ? lookupResult.zoneId : null;
} else {
// We don't have a valid iso country code. This is
// most likely because we're on a test network that's
// using a bogus MCC (eg, "001"), so get a TimeZone
// based only on the NITZ parameters.
OffsetResult lookupResult = mTimeZoneLookupHelper.lookupByNitz(newNitzData);
if (DBG) {
Rlog.d(LOG_TAG, "handleTimeZoneFromNitz: guessZoneIdByNitz returned"
+ " lookupResult=" + lookupResult);
}
zoneId = lookupResult != null ? lookupResult.zoneId : null;
}
}
... if (zoneId != null) {
if (mTimeServiceHelper.isTimeZoneDetectionEnabled()) {
setAndBroadcastNetworkSetTimeZone(zoneId);
}
mNitzTimeZoneDetectionSuccessful = true;
mSavedTimeZoneId = zoneId;
}
...
}
private void handleTimeFromNitz(TimeStampedValue<NitzData> nitzSignal) {
...
if (mTimeServiceHelper.isTimeDetectionEnabled()) {
...
setAndBroadcastNetworkSetTime(logMsg, adjustedCurrentTimeMillis);
}
...
}
/**
* Returns true if automatic time detection is enabled in settings.
*/
public boolean isTimeDetectionEnabled() {
try {
return Settings.Global.getInt(mCr, Settings.Global.AUTO_TIME) > 0;
} catch (Settings.SettingNotFoundException snfe) {
return true;
}
}
/**
* Returns true if automatic time zone detection is enabled in settings.
*/
public boolean isTimeZoneDetectionEnabled() {
try {
return Settings.Global.getInt(mCr, Settings.Global.AUTO_TIME_ZONE) > 0;
} catch (Settings.SettingNotFoundException snfe) {
return true;
}
}
从代码中可以看出只有在数据库对自动同步网络时间/时区为勾选状态时，才会调用setAndBroadcastNetworkSetTime和 setAndBroadcastNetworkSetTimeZone设置当前NITZ解析的时间及时区，并发送广播进行最终的系统时间/时区维护。这里相关数据库的勾选状态获取方法如下，主要判断Settings.Global.AUTO_TIME 及Settings.Global.AUTO_TIME_ZONE 存储值
另外。RIL中mLastNITZTimeInfo值的设定在RadioIndication.java中
public void nitzTimeReceived(int indicationType, String nitzTime, long receivedTime) {
mRil.processIndication(indicationType);
if (RIL.RILJ_LOGD) mRil.unsljLogRet(RIL_UNSOL_NITZ_TIME_RECEIVED, nitzTime);
// todo: Clean this up with a parcelable class for better self-documentation
Object[] result = new Object[2];
result[0] = nitzTime;
result[1] = receivedTime;
boolean ignoreNitz = SystemProperties.getBoolean(
TelephonyProperties.PROPERTY_IGNORE_NITZ, false);
if (ignoreNitz) {
if (RIL.RILJ_LOGD) mRil.riljLog("ignoring UNSOL_NITZ_TIME_RECEIVED");
} else {
if (mRil.mNITZTimeRegistrant != null) {
mRil.mNITZTimeRegistrant.notifyRegistrant(new AsyncResult (null, result, null));
}
// in case NITZ time registrant isn't registered yet, or a new registrant
// registers later
mRil.mLastNITZTimeInfo = result;
}
}
该方法是HAL层，获取nitz
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