Android 应用中怎么监听WiFi的开关状态

package com.yiba.wifi.sdk.lib.presenter;import android.content.BroadcastReceiver;import android.content.Context;import android.content.Intent;import android.content.IntentFilter;import android.net.wifi.WifiManager;public class WifiSwitch_Presenter {  private Context mContext ;  private Receiver receiver ;  private WifiSwitch_Interface mInterface ;  public WifiSwitch_Presenter( Context context , WifiSwitch_Interface mInterface ){    this.mContext = context ;    this.mInterface = mInterface ;    observeWifiSwitch();  }  private void observeWifiSwitch(){    IntentFilter filter = new IntentFilter();    filter.addAction(WifiManager.WIFI_STATE_CHANGED_ACTION);    receiver = new Receiver() ;    mContext.registerReceiver(receiver, filter);  }    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) {      int wifiState = intent.getIntExtra(WifiManager.EXTRA_WIFI_STATE, 0);      switch (wifiState) {        case WifiManager.WIFI_STATE_DISABLED:          if (mInterface != null){            mInterface.wifiSwitchState(WifiSwitch_Interface.WIFI_STATE_DISABLED);          }          break;        case WifiManager.WIFI_STATE_DISABLING:          if (mInterface != null){            mInterface.wifiSwitchState(WifiSwitch_Interface.WIFI_STATE_DISABLING);          }          break;        case WifiManager.WIFI_STATE_ENABLED:          if (mInterface != null){            mInterface.wifiSwitchState(WifiSwitch_Interface.WIFI_STATE_ENABLED);          }          break;        case WifiManager.WIFI_STATE_ENABLING:          if ( mInterface != null ) {            mInterface.wifiSwitchState(WifiSwitch_Interface.WIFI_STATE_ENABLING);          }          break;        case WifiManager.WIFI_STATE_UNKNOWN:          if ( mInterface != null ){            mInterface.wifiSwitchState( WifiSwitch_Interface.WIFI_STATE_UNKNOWN );          }          break;      }    }  }}