这些答案中有许多已经不再适用。

原因是使用vpn(因为冠状病毒，我们现在通过vpn而不是公司的wifi进行测试)

使用苹果的网络框架，并基于这里的代码https://medium.com/@udaykiran.munaga/swift-check-for-internet-connectivity-14e355fa10c5，我能够分别检测到wifi和蜂窝网络。由于使用vpn，路径通常保持满意，因此isConnectedToNetwork()总是返回true。

下面的代码使用了apple Network框架，但重新编写，以便在现有代码中仍然使用Reachability.isConnectedToNetwork()。

    import Network

class Reachability {
    static let shared = Reachability()

    let monitorForWifi = NWPathMonitor(requiredInterfaceType: .wifi)
    let monitorForCellular = NWPathMonitor(requiredInterfaceType: .cellular)
    private var wifiStatus: NWPath.Status = .requiresConnection
    private var cellularStatus: NWPath.Status = .requiresConnection
    var isReachable: Bool { wifiStatus == .satisfied || isReachableOnCellular }
    var isReachableOnCellular: Bool { cellularStatus == .satisfied }

    func startMonitoring() {
        monitorForWifi.pathUpdateHandler = { [weak self] path in
            self?.wifiStatus = path.status

            if path.status == .satisfied {
                DLog.message("Wifi is connected!")
                // post connected notification
            } else {
                DLog.message("No wifi connection.")
                // post disconnected notification
            }
        }
        monitorForCellular.pathUpdateHandler = { [weak self] path in
            self?.cellularStatus = path.status

            if path.status == .satisfied {
                DLog.message("Cellular connection is connected!")
                // post connected notification
            } else {
                DLog.message("No cellular connection.")
                // post disconnected notification
            }
        }

        let queue = DispatchQueue(label: "NetworkMonitor")
        monitorForCellular.start(queue: queue)
        monitorForWifi.start(queue: queue)
    }

    func stopMonitoring() {
        monitorForWifi.cancel()
        monitorForCellular.cancel()
    }
    
    class func isConnectedToNetwork() -> Bool {
        return shared.isReachable
    }
}

然后在你的Appdelegate中didFinishLaunchingWithOptions: start monitoring。

Reachability.shared.startMonitoring()

iOS12 Swift 4和Swift 5

如果你只是想检查连接，你的最低目标是iOS12，那么你可以使用NWPathMonitor

import Network

它需要一些属性的设置。

let internetMonitor = NWPathMonitor()
let internetQueue = DispatchQueue(label: "InternetMonitor")
private var hasConnectionPath = false

我创建了一个函数来启动它。你可以在viewdidload或其他地方做这个。我派了个保镖，你想怎么打就怎么打。

func startInternetTracking() {
    // only fires once
    guard internetMonitor.pathUpdateHandler == nil else {
        return
    }
    internetMonitor.pathUpdateHandler = { update in
        if update.status == .satisfied {
            print("Internet connection on.")
            self.hasConnectionPath = true
        } else {
            print("no internet connection.")
            self.hasConnectionPath = false
        }
    }
    internetMonitor.start(queue: internetQueue)
}

/// will tell you if the device has an Internet connection
/// - Returns: true if there is some kind of connection
func hasInternet() -> Bool {
    return hasConnectionPath
}

现在只需调用helper函数hasInternet()来查看是否有。它实时更新。请参阅Apple文档中的NWPathMonitor。它有更多的功能，如取消()，如果你需要停止跟踪连接，你正在寻找的互联网类型等。 https://developer.apple.com/documentation/network/nwpathmonitor

要在一个实例中检查互联网，可以使用Swift 5

import Foundation
import Alamofire

struct NetworkState {
    var isInternetAvailable:Bool
    {
        return NetworkReachabilityManager()!.isReachable
    }
}

并使用它:

if (NetworkState().isInternetAvailable) {
        //connected to internet
}

这是我的版本。本质上，它没有带来任何新东西。我把它绑定到UIDevice。

import UIKit
import SystemConfiguration

extension UIDevice {

    open class var isConnectedToNetwork: Bool {
        get {
            var zeroAddress = sockaddr_in()
            zeroAddress.sin_len = UInt8(MemoryLayout.size(ofValue: zeroAddress))
            zeroAddress.sin_family = sa_family_t(AF_INET)

            guard
                let defaultRouteReachability: SCNetworkReachability = withUnsafePointer(to: &zeroAddress, {
                    $0.withMemoryRebound(to: sockaddr.self, capacity: 1) {
                        SCNetworkReachabilityCreateWithAddress(nil, $0)
                    }
                }),
                var flags: SCNetworkReachabilityFlags = SCNetworkReachabilityFlags() as SCNetworkReachabilityFlags?,
                SCNetworkReachabilityGetFlags(defaultRouteReachability, &flags)
                else { return false }

            return flags.contains(.reachable) && !flags.contains(.connectionRequired)
        }
    }

}

print("Network status availability: " + ( UIDevice.isConnectedToNetwork ? "true" : "false" ))

struct Connectivity {
    static let sharedInstance = NetworkReachabilityManager()!
    static var isConnectedToInternet:Bool {
        return self.sharedInstance.isReachable
    }
}

现在叫它

if Connectivity.isConnectedToInternet{
    call_your_methods_here()
} else{
    show_alert_for_noInternet()
}

对于Swift 3, Swift 4(使用蜂窝和Wi-Fi):

import SystemConfiguration

public class Reachability {

    class func isConnectedToNetwork() -> Bool {

        var zeroAddress = sockaddr_in(sin_len: 0, sin_family: 0, sin_port: 0, sin_addr: in_addr(s_addr: 0), sin_zero: (0, 0, 0, 0, 0, 0, 0, 0))
        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 = SCNetworkReachabilityFlags(rawValue: 0)
        if SCNetworkReachabilityGetFlags(defaultRouteReachability!, &flags) == false {
            return false
        }

        /* Only Working for WIFI
        let isReachable = flags == .reachable
        let needsConnection = flags == .connectionRequired

        return isReachable && !needsConnection
        */

        // Working for Cellular and WIFI
        let isReachable = (flags.rawValue & UInt32(kSCNetworkFlagsReachable)) != 0
        let needsConnection = (flags.rawValue & UInt32(kSCNetworkFlagsConnectionRequired)) != 0
        let ret = (isReachable && !needsConnection)

        return ret

    }
}

用法:

if Reachability.isConnectedToNetwork(){
    print("Internet Connection Available!")
}else{
    print("Internet Connection not Available!")
}