1、判断手机是否连接到网络，iOS提供了一个SCNetworkReachabilityRef类，方便我们的使用。
2、创建一个工具类，方便全局调用
.h

import <Foundation/Foundation.h>

@interface NetworkUtil : NSObject

• (BOOL)isNetworkReachable;

@end

.m

import "NetworkUtil.h"

import <SystemConfiguration/SCNetworkReachability.h>

import <netdb.h>

@implementation NetworkUtil

// networkチェック

• (BOOL)isNetworkReachable
  {
  // Create zero addy
  //创建零地址，0.0.0.0的地址表示查询本机的网络连接状态
  struct sockaddr_in zeroAddress;
  bzero(&zeroAddress, sizeof(zeroAddress));
  zeroAddress.sin_len = sizeof(zeroAddress);
  zeroAddress.sin_family = AF_INET;

  // Recover reachability flags
  // SCNetworkReachabilityFlags：保存返回的测试连接状态
  // 其中常用的状态有：
  // kSCNetworkReachabilityFlagsReachable：能够连接网络
  // kSCNetworkReachabilityFlagsConnectionRequired：能够连接网络，但是首先得建立连接过程
  // kSCNetworkReachabilityFlagsIsWWAN：判断是否通过蜂窝网覆盖的连接，比如EDGE，GPRS或者目前的3G.主要是区别通过WiFi的连接。
  SCNetworkReachabilityRef defaultRouteReachability = SCNetworkReachabilityCreateWithAddress(NULL,
  (struct sockaddr*)&zeroAddress);
  SCNetworkReachabilityFlags flags;

  BOOL didRetrieveFlags = SCNetworkReachabilityGetFlags(defaultRouteReachability, &flags);
  CFRelease(defaultRouteReachability);

  if (!didRetrieveFlags) {
  return NO;
  }

  BOOL isReachable = flags & kSCNetworkFlagsReachable;
  BOOL needsConnection = flags & kSCNetworkFlagsConnectionRequired;
  return (isReachable && !needsConnection) ? YES : NO;
  }

@end

使用

import "ViewController.h"

import "NetworkUtil.h"

@interface ViewController ()

@end

@implementation ViewController

• (void)viewDidLoad {
  [super viewDidLoad];

  BOOL result = [NetworkUtil isNetworkReachable];

  NSLog(@"是否可以联网：%@",result?@"YES":@"NO");

}

@end