Reachability(判断网络是否连接)

类似于一个网络状况的探针。
　　[[NSNotificationCenter defaultCenter] addObserver: self selector: @selector(reachabilityChanged:) name: kReachabilityChangedNotification object: nil];

    hostReach = [[Reachability reachabilityWithHostName: @"hubj.cnblogs.com"] retain];
    [hostReach startNotifier];

    wifiReach=[[Reachability reachabilityForLocalWiFi]retain];
    [wifiReach startNotifier];

- (void)reachabilityChanged: (NSNotification* )note {
    Reachability* curReach = [note object];
    NSParameterAssert([curReach isKindOfClass: [Reachability class]]);

    NetworkStatus netStatus = [curReach currentReachabilityStatus];

    switch (netStatus)
    {
        case NotReachable:
        {
            NSLog(@"Access Not Available");
            break;
        }

        case ReachableViaWWAN:
        {
            NSLog(@"Reachable WWAN");
            break;
        }
        case ReachableViaWiFi:
        {
            NSLog(@"Reachable WiFi");
            break;
        }
    }

}

判断网络是否连接
/***
* 此函数用来判断是否网络连接服务器正常
* 需要导入Reachability类
*/
+ (BOOL)isExistenceNetwork
{
    BOOL isExistenceNetwork;
    Reachability *reachability = [Reachability reachabilityWithHostName:@""];  // 测试服务器状态

     switch([reachability currentReachabilityStatus]) {
            case NotReachable:
                  isExistenceNetwork = FALSE;
                  break;
             case ReachableViaWWAN:
                   isExistenceNetwork = TRUE;
                   break;
              case ReachableViaWiFi:
                    isExistenceNetwork = TRUE;
                    break;
     }
     return  isExistenceNetwork;
}

实时通知网络状况
/*
* 在应用委托的方法didFinishLaunchingWithOptions中添加
*/

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(reachabilityChanged:) name:kReachabilityChangedNotification object:nil];
reachability = [[Reachability reachabilityWithHostName:@"www.baidu.com"] retain];
[reachability startNotifier];
........
return YES;

/**
*此函数通过判断联网方式，通知给用户
*/
- (void)reachabilityChanged:(NSNotification *)notification
{
      Reachability *curReachability = [notification object];
      NSParameterAssert([curReachability isKindOfClass:[Reachability class]]);
      NetworkStatus curStatus = [curReachability currentReachabilityStatus];
      if(curStatus == NotReachable) {
          [DOIN_Util logFax:@"连接失败"];
      }
}