使用Apple的Reachability代码，我创建了一个函数，可以正确地检查这一点，而无需包含任何类。

在你的项目中包含SystemConfiguration.framework。

进行一些导入:

#import <sys/socket.h>
#import <netinet/in.h>
#import <SystemConfiguration/SystemConfiguration.h>

现在只需调用这个函数:

/*
Connectivity testing code pulled from Apple's Reachability Example: https://developer.apple.com/library/content/samplecode/Reachability
 */
+(BOOL)hasConnectivity {
    struct sockaddr_in zeroAddress;
    bzero(&zeroAddress, sizeof(zeroAddress));
    zeroAddress.sin_len = sizeof(zeroAddress);
    zeroAddress.sin_family = AF_INET;

    SCNetworkReachabilityRef reachability = SCNetworkReachabilityCreateWithAddress(kCFAllocatorDefault, (const struct sockaddr*)&zeroAddress);
    if (reachability != NULL) {
        //NetworkStatus retVal = NotReachable;
        SCNetworkReachabilityFlags flags;
        if (SCNetworkReachabilityGetFlags(reachability, &flags)) {
            if ((flags & kSCNetworkReachabilityFlagsReachable) == 0)
            {
                // If target host is not reachable
                return NO;
            }

            if ((flags & kSCNetworkReachabilityFlagsConnectionRequired) == 0)
            {
                // If target host is reachable and no connection is required
                //  then we'll assume (for now) that your on Wi-Fi
                return YES;
            }


            if ((((flags & kSCNetworkReachabilityFlagsConnectionOnDemand ) != 0) ||
                 (flags & kSCNetworkReachabilityFlagsConnectionOnTraffic) != 0))
            {
                // ... and the connection is on-demand (or on-traffic) if the
                //     calling application is using the CFSocketStream or higher APIs.

                if ((flags & kSCNetworkReachabilityFlagsInterventionRequired) == 0)
                {
                    // ... and no [user] intervention is needed
                    return YES;
                }
            }

            if ((flags & kSCNetworkReachabilityFlagsIsWWAN) == kSCNetworkReachabilityFlagsIsWWAN)
            {
                // ... but WWAN connections are OK if the calling application
                //     is using the CFNetwork (CFSocketStream?) APIs.
                return YES;
            }
        }
    }

    return NO;
}

这是为你测试的iOS 5。

我认为这是最好的答案。

“是”意味着有联系。“No”表示断开连接。

#import "Reachability.h"

 - (BOOL)canAccessInternet
{
    Reachability *IsReachable = [Reachability reachabilityForInternetConnection];
    NetworkStatus internetStats = [IsReachable currentReachabilityStatus];

    if (internetStats == NotReachable)
    {
        return NO;
    }
    else
    {
        return YES;
    }
}

创建一个AFNetworkReachabilityManager对象，并使用以下代码跟踪网络连通性

self.reachabilityManager = [AFNetworkReachabilityManager managerForDomain:@"yourDomain"];
[self.reachabilityManager startMonitoring];
[self.reachabilityManager setReachabilityStatusChangeBlock:^(AFNetworkReachabilityStatus status) {
        switch (status) {
            case AFNetworkReachabilityStatusReachableViaWWAN:
            case AFNetworkReachabilityStatusReachableViaWiFi:
                break;
            case AFNetworkReachabilityStatusNotReachable:
                break;
            default:
                break;
        }
    }];

这是Swift 3.0和异步的。大多数答案是同步解决方案，这将阻塞你的主线程，如果你有一个非常慢的连接。

这个解决方案更好，但并不完美，因为它依赖于谷歌来检查连接，所以可以随意使用另一个URL。

func checkInternetConnection(completionHandler:@escaping (Bool) -> Void)
{
    if let url = URL(string: "http://www.google.com/")
    {
        var request = URLRequest(url: url)
        request.httpMethod = "HEAD"
        request.cachePolicy = .reloadIgnoringLocalAndRemoteCacheData
        request.timeoutInterval = 5

        let tast = URLSession.shared.dataTask(with: request, completionHandler:
        {
            (data, response, error) in

            completionHandler(error == nil)
        })
        tast.resume()
    }
    else
    {
        completionHandler(true)
    }
}

Swift 3 / Swift 4

您必须首先导入

import SystemConfiguration

您可以通过以下方法检查Internet连接。

func isConnectedToNetwork() -> Bool {

    var zeroAddress = sockaddr_in()
    zeroAddress.sin_len = UInt8(MemoryLayout.size(ofValue: zeroAddress))
    zeroAddress.sin_family = sa_family_t(AF_INET)

    let defaultRouteReachability = withUnsafePointer(to: &zeroAddress) {
        $0.withMemoryRebound(to: sockaddr.self, capacity: 1) {zeroSockAddress in
            SCNetworkReachabilityCreateWithAddress(nil, zeroSockAddress)
        }
    }

    var flags = SCNetworkReachabilityFlags()
    if !SCNetworkReachabilityGetFlags(defaultRouteReachability!, &flags) {
        return false
    }
    let isReachable = (flags.rawValue & UInt32(kSCNetworkFlagsReachable)) != 0
    let needsConnection = (flags.rawValue & UInt32(kSCNetworkFlagsConnectionRequired)) != 0
    return (isReachable && !needsConnection)
}

这曾经是正确的答案，但现在已经过时了，因为你应该订阅通知以获得可访问性。这个方法同步检查:

你可以使用苹果的Reachability类。它还可以让你检查是否启用了Wi-Fi:

Reachability* reachability = [Reachability sharedReachability];
[reachability setHostName:@"www.example.com"];    // Set your host name here
NetworkStatus remoteHostStatus = [reachability remoteHostStatus];

if (remoteHostStatus == NotReachable) { }
else if (remoteHostStatus == ReachableViaWiFiNetwork) { }
else if (remoteHostStatus == ReachableViaCarrierDataNetwork) { }

Reachability类并没有随SDK一起发布，而是作为这个Apple示例应用程序的一部分。只需下载它，并复制Reachability.h/m到您的项目。另外，您必须将SystemConfiguration框架添加到您的项目中。