requestLocationUpdates为空无法获取当前位置
LocationManager lm = (LocationManager) context.getSystemService(Context.LOCATION_SERVICE);
Criteria c = new Criteria();
c.setAccuracy(Criteria.ACCURACY_COARSE);
c.setSpeedRequired(false);
c.setCostAllowed(false);
c.setBearingRequired(false);
c.setAltitudeRequired(false);
c.setPowerRequirement(Criteria.POWER_LOW);
String bestProvider = lm.getBestProvider(c, true);
Location location = lm.getLastKnownLocation(bestProvider);
location 返回null求助