在项目中创建一个新的Swift文件，命名为Reachability.swift。将以下代码剪切并粘贴到其中以创建您的类。

import Foundation
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(sizeofValue(zeroAddress))
        zeroAddress.sin_family = sa_family_t(AF_INET)

        let defaultRouteReachability = withUnsafePointer(&zeroAddress) {
            SCNetworkReachabilityCreateWithAddress(kCFAllocatorDefault, UnsafePointer($0))
        }

        var flags: SCNetworkReachabilityFlags = SCNetworkReachabilityFlags(rawValue: 0)
        if SCNetworkReachabilityGetFlags(defaultRouteReachability!, &flags) == false {
             return false
        }

        let isReachable = flags == .Reachable
        let needsConnection = flags == .ConnectionRequired

        return isReachable && !needsConnection

    }
}

你可以使用下面的代码检查项目中的任何地方的互联网连接:

if Reachability.isConnectedToNetwork() {
    println("Internet connection OK")
} else {
    println("Internet connection FAILED")
}

如果用户没有连接到互联网，您可能希望向他们显示一个警告对话框来通知他们。

if Reachability.isConnectedToNetwork() {
    println("Internet connection OK")
} else {
    println("Internet connection FAILED")
    var alert = UIAlertView(title: "No Internet Connection", message: "Make sure your device is connected to the internet.", delegate: nil, cancelButtonTitle: "OK")
    alert.show()
}

解释:

我们正在制作一个可重用的公共类和方法，可以在项目的任何地方使用，以检查互联网连接。我们需要添加基础和系统配置框架。

在公共类Reachability中，方法isConnectedToNetwork() -> Bool{}将返回一个关于互联网连接的Bool值。我们使用if循环对case执行所需的操作。我希望这足够了。干杯!

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" ))

虽然没有直接回答你的问题，但我想提一下苹果公司最近有这样一个谈话:

https://developer.apple.com/videos/play/wwdc2018/714/

大约在9点55分，他谈到了做你正在问的事情:

检查连接 如果连接->做点什么 如果没有连接->执行其他操作(等待?重试?)

然而，这有一些陷阱:

如果在第二步中，它说它有连接，但0.5秒后他就没有了呢? 如果用户在代理的后面呢 最后但并非最不重要的是，如果这里的一些答案不能确定连通性呢?(我敢肯定，如果你快速切换你的连接，去wi-fi，然后关掉它(只是让它变得复杂)，它几乎永远不能正确地判断我是否获得了连接)。 视频中说:“没有办法保证未来的行动是否会成功。”

以下是苹果公司的一些最佳实践:

设置waitsForConnectivity为true (https://developer.apple.com/documentation/foundation/urlsessionconfiguration/2908812-waitsforconnectivity) 响应委托方法taskIsWaitingForConnectivity (https://developer.apple.com/documentation/foundation/urlsessiontaskdelegate/2908819-urlsession)。这是苹果推荐的检查连接的方法，正如33:25的视频中提到的那样。

根据谈话，不应该有任何理由预先检查你是否有互联网连接，因为在你向服务器发送请求时，它可能并不准确。

从iOS 12开始，NWPathMonitor取代了Reachability。用这个:

import Network


struct Internet {
 
 private static let monitor = NWPathMonitor()
 
 static var active = false
 static var expensive = false
 
 /// Monitors internet connectivity changes. Updates with every change in connectivity.
 /// Updates variables for availability and if it's expensive (cellular).
 static func start() {
  guard monitor.pathUpdateHandler == nil else { return }
  
  monitor.pathUpdateHandler = { update in
   Internet.active = update.status == .satisfied ? true : false
   Internet.expensive = update.isExpensive ? true : false
  }
  
  monitor.start(queue: DispatchQueue(label: "InternetMonitor"))
 }
 
}

在使用:

Internet.start()

if Internet.active {
 // do something
}
  
if Internet.expensive {
 // device is using Cellular data or WiFi hotspot
}

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!")
}