Android应用中怎么监听手机GPS的打开状态

package com.yiba.core;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.location.LocationManager;

/**
 * Created by ${zhaoyanjun} on 2017/3/29.
 * GPS 开关监听
 */

public class GPS_Presenter {
  private Context mContext ;
  private Receiver receiver ;
  private GPS_Interface mInterface ;
  private String GPS_ACTION = "android.location.PROVIDERS_CHANGED" ;


  public GPS_Presenter(Context context , GPS_Interface mInterface ){
    this.mContext = context ;
    this.mInterface = mInterface ;

    observeWifiSwitch();
  }

  private void observeWifiSwitch(){
    IntentFilter filter = new IntentFilter();
    filter.addAction( GPS_ACTION );
    receiver = new Receiver() ;
    mContext.registerReceiver(receiver, filter);
  }

  /**
   * 释放资源
   */
  public void onDestroy(){
    if ( receiver != null ){
      mContext.unregisterReceiver( receiver );
    }
    if (mContext!=null){
      mContext = null;
    }
  }

  class Receiver extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {
      if (intent.getAction().matches( GPS_ACTION )) {
         if ( mInterface != null ){
           mInterface.gpsSwitchState( gpsIsOpen( context ));
         }
      }
    }
  }

  /**
   * 判断GPS是否开启，GPS或者AGPS开启一个就认为是开启的
   * @param context
   * @return true 表示开启
   */
  public boolean gpsIsOpen(final Context context) {
    LocationManager locationManager
        = (LocationManager) context.getApplicationContext().getSystemService(Context.LOCATION_SERVICE);
    // 通过GPS卫星定位，定位级别可以精确到街（通过24颗卫星定位，在室外和空旷的地方定位准确、速度快）
    boolean gps = locationManager.isProviderEnabled(LocationManager.GPS_PROVIDER);
    // 通过WLAN或移动网络(3G/2G)确定的位置（也称作AGPS，辅助GPS定位。主要用于在室内或遮盖物（建筑群或茂密的深林等）密集的地方定位）
    boolean network = locationManager.isProviderEnabled(LocationManager.NETWORK_PROVIDER);
    if (gps || network) {
      return true;
    }

    return false;
  }
}

package com.yiba.core;

/**
 * Created by ${zhaoyanjun} on 2017/3/29.
 * gps 开关监听
 */

public interface GPS_Interface {
  void gpsSwitchState( boolean gpsOpen );
}

package com.yiba.core;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity implements GPS_Interface {

  private GPS_Presenter gps_presenter ;

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    gps_presenter = new GPS_Presenter( this , this ) ;

  }

  @Override
  protected void onDestroy() {
    super.onDestroy();

    //释放资源
    if ( gps_presenter != null ){
      gps_presenter.onDestroy();
    }
  }

  @Override
  public void gpsSwitchState(boolean gpsOpen) {
    if ( gpsOpen ){
      Toast.makeText(this, " 手机GPS 打开", Toast.LENGTH_SHORT).show();
    }else {
      Toast.makeText(this, " 手机GPS 关闭", Toast.LENGTH_SHORT).show();
    }
  }
}