IOS-网络（监听网络状态）

 //
 //  BWNetWorkTool.h
 //  IOS_0131_检测网络状态
 //
 //  Created by ma c on 16/1/31.
 //  Copyright © 2016年 博文科技. All rights reserved.
 //

 #import <Foundation/Foundation.h>

 @interface BWNetWorkTool : NSObject
 ///是否是WiFi
 + (BOOL)isEnableWiFi;
 ///是否是3G
 + (BOOL)isEnable3G;

 @end

 //
 //  BWNetWorkTool.m
 //  IOS_0131_检测网络状态
 //
 //  Created by ma c on 16/1/31.
 //  Copyright © 2016年 博文科技. All rights reserved.
 //

 #import "BWNetWorkTool.h"
 #import "Reachability.h"

 @implementation BWNetWorkTool

 //是否是WiFi
 + (BOOL)isEnableWiFi
 {
     return [[Reachability reachabilityForLocalWiFi] currentReachabilityStatus] !=NotReachable;
 }
 //是否是3G
 + (BOOL)isEnable3G
 {
     return [[Reachability reachabilityForInternetConnection] currentReachabilityStatus] !=NotReachable;
 }

 @end

 //
 //  ViewController.m
 //  IOS_0131_检测网络状态
 //
 //  Created by ma c on 16/1/31.
 //  Copyright © 2016年 博文科技. All rights reserved.
 //

 #import "ViewController.h"
 #import "Reachability.h"
 #import "BWNetWorkTool.h"

 @interface ViewController ()

 @property (nonatomic, strong) Reachability *reachability;

 @end

 @implementation ViewController
 /*
  检测网络状态
  1.在网络应用中，需要对用户设备的网络状态进行实时监控，目的：
    a.让用户了解自己的网络状态，防止一些误会（怪应用无能）
    b.根据用户的网络状态进行智能处理，节省用户流量，提高用户体验
      WIFI/3G/4G网络：自动下载高清图片
             低速网络：只能下载缩略图
             没有网络：智能显示离线的缓存数据
    c.苹果官方提供了一个叫Reachability的示例程序，便于开发者检测网络状态
      https://developer.apple.com/library/ios/samplecode/Reachability/Reachability.zip

  2.Reachability的使用步骤
  1>添加框架SystemConfiguration.framework
  2>添加源代码
  3>包含头文件 - #import "Reachability.h"

  3.常见用法
  1>是否是WiFi
  + (BOOL)isEnableWiFi
  {
  return [[Reachability reachabilityForLocalWiFi] currentReachabilityStatus] !=NotReachable;
  }
  2>是否是3G
  + (BOOL)isEnable3G
  {
  return [[Reachability reachabilityForInternetConnection] currentReachabilityStatus] !=NotReachable;
  }
  */

 - (void)viewDidLoad {
     [super viewDidLoad];

     //监听网络状态发生改变通知
     [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(networkStateChange) name:kReachabilityChangedNotification object:nil];

     //获得Reachability对象
     self.reachability = [Reachability reachabilityForInternetConnection];

     //开始监控
     [self.reachability startNotifier];

 //    //获取Reachability对象
 //    Reachability *wifi = [Reachability reachabilityForLocalWiFi];
 //    //获取Reachability对象的当前网络状态
 //    NetworkStatus wifiStatus = wifi.currentReachabilityStatus;
 //
 //    if (wifiStatus !=NotReachable) {
 //        NSLog(@"wifi");
 //    }

 }

 - (void)networkStateChange
 {
     NSLog(@"网络状态改变了");
     [self changeNetworkState];
 }

 - (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
 {
     [self changeNetworkState];
 }

 - (void)changeNetworkState
 {
     if ([BWNetWorkTool isEnableWiFi]) {
         NSLog(@"WiFi环境");
     }else if ([BWNetWorkTool isEnable3G]){
         NSLog(@"手机自带网络");
     }else{
         NSLog(@"没有网络");
     }
 }

 - (void)dealloc
 {
     [self.reachability stopNotifier];
     [[NSNotificationCenter defaultCenter] removeObserver:self];
 }

 @end