I use this one:

LocationManager.requestLocationUpdates(String provider, long minTime, float minDistance, LocationListener listener)

For example, using a 1s interval:

locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER,1000,0,this);

the time is in milliseconds, the distance is in meters.

This automatically calls:

public void onLocationChanged(Location location) {
    //Code here, location.getAccuracy(), location.getLongitude() etc...
}

I also had these included in the script but didnt actually use them:

public void onStatusChanged(String provider, int status, Bundle extras) {}
public void onProviderEnabled(String provider) {}
public void onProviderDisabled(String provider) {}

In short:

public class GPSClass implements LocationListener {

    public void onLocationChanged(Location location) {
        // Called when a new location is found by the network location provider.
        Log.i("Message: ","Location changed, " + location.getAccuracy() + " , " + location.getLatitude()+ "," + location.getLongitude());
    }

    public void onStatusChanged(String provider, int status, Bundle extras) {}
    public void onProviderEnabled(String provider) {}
    public void onProviderDisabled(String provider) {}

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        locationManager = (LocationManager)getSystemService(Context.LOCATION_SERVICE);
        locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER,1000,0,this);
    }
}

For the getLastKnownLocation method, it is said in the documentation :

If the provider is currently disabled, null is returned.

Which means your GPS is disabled.

For the requestLocationUpdates, you are requesting a location every 20 seconds, try to decrease this number so you know at least if your program is working.

You can try this :

LocationManager locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, this);

Also I really advise you to use the new API to request location updates : https://developer.android.com/training/location/receive-location-updates.html

It is very fast and accurate, but you need to create a google developer account (for free) and create an api key. All needed information should be in the link.

It happens with emulators, try rebooting the emulator.

Or, close both eclipse and emulator and start both again

You could register it multiple times. see my code below.

package com.test.locationmanager;

import android.app.Activity;
import android.content.Context;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.location.LocationProvider;
import android.os.Bundle;
import android.widget.TextView;

public class LocationManagerStatus extends Activity {

private LocationManager locationManager;
private TextView textView;
private final LocationListener gpsLocationListener =new LocationListener(){

    @Override
    public void onStatusChanged(String provider, int status, Bundle extras) {
        final String tvTxt = textView.getText().toString();
        switch (status) {
        case LocationProvider.AVAILABLE:
            textView.setText(tvTxt + "GPS available again\n");
            break;
        case LocationProvider.OUT_OF_SERVICE:
            textView.setText(tvTxt + "GPS out of service\n");
            break;
        case LocationProvider.TEMPORARILY_UNAVAILABLE:
            textView.setText(tvTxt + "GPS temporarily unavailable\n");
            break;
        }
    }

    @Override
    public void onProviderEnabled(String provider) {
        textView.setText(textView.getText().toString()
                + "GPS Provider Enabled\n");
    }

    @Override
    public void onProviderDisabled(String provider) {
        textView.setText(textView.getText().toString()
                + "GPS Provider Disabled\n");
    }

    @Override
    public void onLocationChanged(Location location) {
        locationManager.removeUpdates(networkLocationListener);
        textView.setText(textView.getText().toString()
                + "New GPS location: "
                + String.format("%9.6f", location.getLatitude()) + ", "
                + String.format("%9.6f", location.getLongitude()) + "\n");
    }
};
private final LocationListener networkLocationListener =
                                                    new LocationListener(){

    @Override
    public void onStatusChanged(String provider, int status, Bundle extras){
        final String tvTxt = textView.getText().toString();
        switch (status) {
        case LocationProvider.AVAILABLE:
            textView.setText(tvTxt + "Network location available again\n");
            break;
        case LocationProvider.OUT_OF_SERVICE:
            textView.setText(tvTxt + "Network location out of service\n");
            break;
        case LocationProvider.TEMPORARILY_UNAVAILABLE:
            textView.setText(tvTxt
                    + "Network location temporarily unavailable\n");
            break;
        }
    }

    @Override
    public void onProviderEnabled(String provider) {
        textView.setText(textView.getText().toString()
                + "Network Provider Enabled\n");
    }

    @Override
    public void onProviderDisabled(String provider) {
        textView.setText(textView.getText().toString()
                + "Network Provider Disabled\n");
    }

    @Override
    public void onLocationChanged(Location location) {
        textView.setText(textView.getText().toString()
                + "New network location: "
                + String.format("%9.6f", location.getLatitude()) + ", "
                + String.format("%9.6f", location.getLongitude()) + "\n");
    }
};

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    textView = (TextView) findViewById(R.id.textview);
    locationManager = (LocationManager) 
            getSystemService(Context.LOCATION_SERVICE);
}

@Override
protected void onResume() {
    super.onResume();
    locationManager.requestLocationUpdates(
            LocationManager.NETWORK_PROVIDER, 5000, 0,
            networkLocationListener);
    locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER,
            3000, 0, gpsLocationListener);
}

@Override
protected void onPause() {
    super.onPause();
    locationManager.removeUpdates(networkLocationListener);
    locationManager.removeUpdates(gpsLocationListener);
}
}

Don't store Location class in shared preferences In my case this was the problem

As per my understanding it should be OR. Read this blog for more info.

Keep in mind that GPS has an accuracy of 10 to 50 meters itself.

The best way to do this is not through requestLocationUpdates, but rather through using a timer to start updates periodically. That should spare you from wearing out your battery needlessly. So I end up doing something like this:

1. I have some checks to see if I like the GPS value.
2. If I'm satisfied with the GPS, then I remove updates, and start a timer to start getting updates again.
3. I always get updates upon resuming the application.

Code to restart the GPS updates might look like this:

Timer mTimer;
private void sendFinalGps() {
    mLocationManager.removeUpdates(this);
    mTimer = new Timer();
    mTimer.schedule(new findGpsTime(), getTimeBetweenUpdates());
}