Check and prompt user to enable GPS

To check if the GPS have been enabled or not, the following code can be used:

String provider = Settings.Secure.getString(getContentResolver(), Settings.Secure.LOCATION_PROVIDERS_ALLOWED);

If it's empty, means the GPS have not been enabled. You can start activity with intent Settings.ACTION_SECURITY_SETTINGS, to switch to GPS setting page.

package com.exercise.AndroidEnableGPS;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.provider.Settings;
import android.widget.Toast;

public class AndroidEnableGPS extends Activity {
   /** Called when the activity is first created. */
   @Override
   public void onCreate(Bundle savedInstanceState) {
       super.onCreate(savedInstanceState);
       setContentView(R.layout.main);
      
       CheckEnableGPS();
   }
  
   private void CheckEnableGPS(){
    String provider = Settings.Secure.getString(getContentResolver(),
      Settings.Secure.LOCATION_PROVIDERS_ALLOWED);
       if(!provider.equals("")){
           //GPS Enabled
        Toast.makeText(AndroidEnableGPS.this, "GPS Enabled: " + provider,
          Toast.LENGTH_LONG).show();
       }else{
        Intent intent = new Intent(Settings.ACTION_SECURITY_SETTINGS);
           startActivity(intent);
       }

   }
}

Download the files.