状态切换剖析之IDLE_PENDING–>SENSING的最后部分提到了从SENSING状态向LOCATION切换的一个入口，这篇将接上文来继续阐述SENSING状态是如何切换到LOCATION的。
在SENSING状态下最后所做的一件事就是启动了MotionDector来监测是否设备是否有位移发生，监测的结果会通过回调函数返回。如果状态是RESULT_STATIONARY并且当前状态为SENSING那么将调用stepIdleStateLocked来开始切换。
@Override
public void onAnyMotionResult(int result) {
if (DEBUG) Slog.d(TAG, "onAnyMotionResult(" + result + ")");
if (result == AnyMotionDetector.RESULT_MOVED) {
if (DEBUG) Slog.d(TAG, "RESULT_MOVED received.");
synchronized (this) {
handleMotionDetectedLocked(mConstants.INACTIVE_TIMEOUT, "sense_motion");
}
} else if (result == AnyMotionDetector.RESULT_STATIONARY) {
if (DEBUG) Slog.d(TAG, "RESULT_STATIONARY received.");
if (mState == STATE_SENSING) {
// If we are currently sensing, it is time to move to locating.
synchronized (this) {
mNotMoving = true;
stepIdleStateLocked();
}
} else if (mState == STATE_LOCATING) {
// If we are currently locating, note that we are not moving and step
// if we have located the position.
synchronized (this) {
mNotMoving = true;
if (mLocated) {
stepIdleStateLocked();
}
}
}
}
}
在stepIdleStateLocked方法中判断当前为SENSING的状态，然后做了几件事：1）修改当前状态；2）设置Alarm；3）设置位置监听
case STATE_SENSING:
mState = STATE_LOCATING;
if (DEBUG) Slog.d(TAG, "Moved from STATE_SENSING to STATE_LOCATING.");
EventLogTags.writeDeviceIdle(mState, "step");
cancelSensingAlarmLocked();
scheduleSensingAlarmLocked(mConstants.LOCATING_TIMEOUT);
mLocating = true;
mLocationManager.requestLocationUpdates(mLocationRequest, mGenericLocationListener,
mHandler.getLooper());
if (mLocationManager.getProvider(LocationManager.GPS_PROVIDER) != null) {
mHaveGps = true;
mLocationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 1000, 5,
mGpsLocationListener, mHandler.getLooper());
} else {
mHaveGps = false;
}
break;
第一点，也就是简单的将变量mState的值赋值为了STATE_LOCATING。第二点做的事一如前面几种状态中做过的一样，设置一个Alarm来作为下个状态切换的触发器。在设置之前首先要cancel以前的Alarm，这个被取消的广播类型就是ACTION_STEP_IDLE_STATE，也就是触发状态切换的广播。然后调用scheduleSensingAlarmLocked(mConstants.LOCATING_TIMEOUT)方法来重新设置Alarm，这个Alarm的deley时间就是LOCATING_TIMEOUT。
LOCATING_TIMEOUT = mParser.getLong(KEY_LOCATING_TIMEOUT,
!DEBUG ? 30 * 1000L : 15 * 1000L);
默认DEBUG为false，所以这个timeout默认为30秒，后面也会介绍到在这30秒的时间内用来检测设备的运动状态而在scheduleSensingAlarmLocked方法中看到又进行了一次取消alarm的操作，这里是不是多余的呢？之前刚进行过一次取消。
void scheduleSensingAlarmLocked(long delay) {
if (DEBUG) Slog.d(TAG, "scheduleSensingAlarmLocked(" + delay + ")");
cancelSensingAlarmLocked();
mNextAlarmTime = SystemClock.elapsedRealtime() + delay;
mAlarmManager.set(AlarmManager.ELAPSED_REALTIME_WAKEUP,
mNextAlarmTime, mSensingAlarmIntent);
mSensing = true;
}
第三点就是设置位置监听，首先将mLocating标志位置为true，也就是标示注册了位置监听服务，在后面的取消位置监听时作为标志位来判断。然后通过LocationManager了请求了位置监听服务，先是申请了通过手机本身传感器精度为ACCURACY_FINE的定位服务
mLocationRequest = new LocationRequest()
.setQuality(LocationRequest.ACCURACY_FINE)
.setInterval(0)
.setFastestInterval(0)
.setNumUpdates(1);
而监听器的定义如下
private final LocationListener mGenericLocationListener = new LocationListener() {
@Override
public void onLocationChanged(Location location) {
synchronized (DeviceIdleController.this) {
receivedGenericLocationLocked(location);
}
}
@Override
public void onStatusChanged(String provider, int status, Bundle extras) {
}
@Override
public void onProviderEnabled(String provider) {
}
@Override
public void onProviderDisabled(String provider) {
}
};
在触发位置变化时去调用receivedGenericLocationLocked(location)
void receivedGenericLocationLocked(Location location) {
if (mState != STATE_LOCATING) {
cancelLocatingLocked();
return;
}
if (DEBUG) Slog.d(TAG, "Generic location: " + location);
mLastGenericLocation = new Location(location);
if (location.getAccuracy() > mConstants.LOCATION_ACCURACY && mHaveGps) {
return;
}
mLocated = true;
if (mNotMoving) {
stepIdleStateLocked();
}
}
如果开启了Gps的定位监测，并且精度大于LOCATION_ACCURACY，那么这里的监测就忽略(用更精确的GPS数据)，用Gps的监测数据，在后面会讲到。否则,如果监测数据为Not move，那么就调用StepIdleStateLocked来进行下一步。在此同时，也去检测了是否支持GPS
mLocationManager.requestLocationUpdates(mLocationRequest, mGenericLocationListener,
mHandler.getLooper());
if (mLocationManager.getProvider(LocationManager.GPS_PROVIDER) != null) {
mHaveGps = true;
mLocationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 1000, 5,
mGpsLocationListener, mHandler.getLooper());
} else {
mHaveGps = false;
}
如果支持的话就申请注册GPS的位置监测服务，以提供准确度。同时前面ACCURACY_FINE的定位服务实际上就被架空了。来看下这个监听器的定义。
private final LocationListener mGpsLocationListener = new LocationListener() {
@Override
public void onLocationChanged(Location location) {
synchronized (DeviceIdleController.this) {
receivedGpsLocationLocked(location);
}
}
重点还是onLocationChanged时调用的receivedGpsLocationLocked方法，和receivedGenericLocationLocked类似
void receivedGpsLocationLocked(Location location) {
if (mState != STATE_LOCATING) {
cancelLocatingLocked();
return;
}
if (DEBUG) Slog.d(TAG, "GPS location: " + location);
mLastGpsLocation = new Location(location);
if (location.getAccuracy() > mConstants.LOCATION_ACCURACY) {
return;
}
mLocated = true;
if (mNotMoving) {
stepIdleStateLocked();
}
}
和前面的类似，在结果为not move的时候调用stepIdleStateLocked来进入下一步操作。
至此从SENSING状态切换到LOCATION状态的动作就完成了。