需要注意的地方：在获取完网络之后，需要Reachability移除这个对象，[self removeNetworkListener], 不然会一直加载

1.下载苹果官方工具类：https://developer.apple.com/library/ios/samplecode/Reachability/Reachability.zip

2.有用的文件只有两个，Reachability.h，Reachability.m

3.在需要检测的地方导入头文件 #import "Reachability.h"

引入成员变量 @property (nonatomic) Reachability *reachability;

4.代码：

-(void)listenNetwork{

    //注册网络状态通知

    [[NSNotificationCenter defaultCenter]addObserver:self selector:@selector(networkStatusChanged:) name:kReachabilityChangedNotification object:nil];

    //获取Reachability对象

    self.reachability = [Reachability reachabilityForInternetConnection];

    //开始监听网络变化

    [self.reachability startNotifier];

    // 立即进行一次初始的网络状态检测

    NetworkStatus networkStatus = [self.reachability currentReachabilityStatus];

    [self networkStatusChangedWithNetworkStatus:networkStatus];

}

- (void)networkStatusChanged:(NSNotification*)notification {

    Reachability*reachability = (Reachability*)notification.object;

    NetworkStatusnetworkStatus = [reachabilitycurrentReachabilityStatus];

    [self networkStatusChangedWithNetworkStatus:networkStatus];

}

- (void)networkStatusChangedWithNetworkStatus:(NetworkStatus)networkStatus {

    // 判断是否有网络连接

    if(networkStatus ==NotReachable) {

        NSLog(@"无网络连接");

    }else{

//这里调用自己加载数据的方法

        NSLog(@"有网络连接");

    }

}- (void)dealloc{

    [self removeNetworkListener];

}

-(void)removeNetworkListener{

    [self.reachability stopNotifier];

    [[NSNotificationCenter defaultCenter] removeObserver:self name:kReachabilityChangedNotification object:nil];

    self.reachability = nil;

}