App内网络监测 当链接到网络时及时通知页面请求数据

#检测网络状态 在你的工程里引入

pod 'Reachability', '~> 3.2'

 在AppDelegate 

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {

 [self performSelector:@selector(networkCheckUp) withObject:nil afterDelay:0.5];//网络监听

}
#pragma mark网络监听
-(void)networkCheckUp{
    //开启网络状况的监听
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(reachabilityChanged:) name: kReachabilityChangedNotification object: nil];
    hostReach = [Reachability reachabilityWithHostName:@"http://www.baidu.com"];//可以以多种形式初始化
    [hostReach startNotifier];  //开始监听,会启动一个run loop
    [self updateInterfaceWithReachability: hostReach];

}

//监听到网络状态改变
- (void) reachabilityChanged: (NSNotification* )note {
    Reachability* curReach = [note object];
    NSParameterAssert([curReach isKindOfClass: [Reachability class]]);
    [self updateInterfaceWithReachability: curReach];
}


//处理连接改变后的情况
- (void) updateInterfaceWithReachability: (Reachability*) curReach {
    //对连接改变做出响应的处理动作。
    NetworkStatus status = [curReach currentReachabilityStatus];
    if(status == ReachableViaWWAN ||status == ReachableViaWiFi)//3g 4g 2g wifi
    {//NETWORKING
        [[NSNotificationCenter defaultCenter]postNotificationName:NETWORKING object:nil];//有网的时候通知页面刷新数据
    
    } else {
         NSLog(@"
---无网络
");
    }
}

　　检查当前网络环境
    程序启动时，如果想检测可用的网络环境，可以像这样
    // 是否wifi
    + (BOOL) IsEnableWIFI {
        return ([[Reachability reachabilityForLocalWiFi] currentReachabilityStatus] != NotReachable);
    }

    // 是否3G
    + (BOOL) IsEnable3G {
        return ([[Reachability reachabilityForInternetConnection] currentReachabilityStatus] != NotReachable);
    }
    例子：
    - (void)viewWillAppear:(BOOL)animated {    
    if (([Reachability reachabilityForInternetConnection].currentReachabilityStatus == NotReachable) && 
            ([Reachability reachabilityForLocalWiFi].currentReachabilityStatus == NotReachable)) {
            self.navigationItem.hidesBackButton = YES;
            [self.navigationItem setLeftBarButtonItem:nil animated:NO];
        }
    }

其他类似问题可以参考  http://blog.csdn.net/xbiii3s/article/details/6612139