问题
What I want to do is to get the location latitude and longitude each time a function is called. As I have understood the best way to do that is to leave the location update for a few seconds to get the correct fix and then disable it, but I can't make it work in my app.
What I have managed until now is to get the last known location of the phone, every time the displayData function is called, but I have not been able to get over all the errors that appear when I'm trying to change to requestLocationUpdates. What exactly I am doing here is to call the displayData function, when there is incoming data from a bluetooth device, in order to get the location and write the data + location in a file.
Can someone help me because all the guides show how to trigger something when location updates but I don't want to do that. I just want a correct location periodically...
private void displayData(final byte[] byteArray) {
try {
mFusedLocationClient.getLastLocation()
.addOnSuccessListener(this, new OnSuccessListener<Location>() {
@Override
public void onSuccess(Location location) {
// Got last known location. In some rare situations this can be null.
if (byteArray != null) {
String data = new String(byteArray);
tv.setText(n/2 + " measurements since startup...");
n += 1;
if (location != null) {
double lat = location.getLatitude();
double lng = location.getLongitude();
latitude = String.valueOf(lat);
longitude = String.valueOf(lng);
}
try
{
FileWriter fw = new FileWriter(textfile,true); //the true will append the new data
if (writeDate()) {
fw.write("\n");
fw.write(stringDate);
fw.write(data); //appends the string to the file
}
else {
fw.write(data); //appends the string to the file
fw.write(" - ");
fw.write(latitude);
fw.write(",");
fw.write(longitude);
}
fw.close();
}
catch(IOException ioe)
{
System.err.println("IOException: " + ioe.getMessage());
}
// find the amount we need to scroll. This works by
// asking the TextView's internal layout for the position
// of the final line and then subtracting the TextView's height
final int scrollAmount = tv.getLayout().getLineTop(
tv.getLineCount())
- tv.getHeight();
// if there is no need to scroll, scrollAmount will be <=0
if (scrollAmount > 0)
tv.scrollTo(0, scrollAmount);
else
tv.scrollTo(0, 0);
}
}
});
} catch (SecurityException e) {
// lets the user know there is a problem with the gps
}
}
回答1:
Here's what I understand of your problem:
- You want GPS location on demand, but:
- You don't want the GPS to run constantly, and:
- You accept that the GPS will have to be run for a short period of time
Try not to think in terms of a "function that returns the phone's current location", because that implies that it's a simple, synchronous operation that provides an answer without blocking. We can't do that here.
Instead, I suggest you think of this more as an FSM, since you need an arbitrary amount of time (perhaps a few seconds, perhaps more) between the time you call displayData() and the time you start getting real-time GPS fixes. In other words, displayData() will not produce a location, directly; it'll set into motion a chain of events which eventually results in you obtaining a location.
You'll have to commit to using requestLocationUpdates() (or a similar method):
private void displayData(final byte[] byteArray) {
//This call turns the GPS on, and returns immediately:
locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, new LocationListener() {
//This function gets called some time after displayData() returns (possibly
//*way* after). It executes on the UI thread.
public void onLocationChanged(Location location) {
locationManager.removeUpdates(this); //Shut down the GPS
//(Execute the remainder of your onSuccess() logic here.)
//Now our state machine is complete, and everything is cleaned up.
//We are ready for the next call to displayData().
}
public void onStatusChanged(String provider, int status, Bundle extras) {}
public void onProviderEnabled(String provider) {}
public void onProviderDisabled(String provider) {}
);
}
That way,
- We don't block the UI thread (
displayData()returns immediately) - The state machine eventually converges to an answer (provided the GPS is functional)
- GPS turns off once we have the information we need
Some improvements to this scheme you might want to consider:
- A way to avoid a repeat call to
requestLocationUpdates()ifdisplayData()gets called before the previous request has resolved - Handling the case where the UI elements referred to in your
onSuccess()method are no longer available b/c the Activity hasonDestroy()'dduring the time the GPS request was "in progress" - Cancelling the request-in-progress if you need to clean up, etc.
回答2:
I followed Markus Kauppinen's approach requesting for location updates at a time interval that suits my app and then just using the get last known location when there is incoming data from bluetooth. So I just added the following in my activity:
LocationRequest mLocationRequest = new LocationRequest();
mLocationRequest.setInterval(30000);
mLocationRequest.setFastestInterval(10000);
mLocationRequest.setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY);
LocationCallback mLocationCallback = new LocationCallback();
// Register the listener with the Location Manager to receive location updates
try {
mFusedLocationClient.requestLocationUpdates(mLocationRequest,
mLocationCallback,
null /* Looper */);
}
catch (SecurityException e) {
// lets the user know there is a problem with the gps
}
来源：https://stackoverflow.com/questions/53614643/how-can-i-get-the-current-gps-location-every-time-a-function-is-called