斯威夫特5

import SystemConfiguration    

protocol Utilities {}
extension NSObject: Utilities {
    enum ReachabilityStatus {
        case notReachable
        case reachableViaWWAN
        case reachableViaWiFi
    }
    
    var currentReachabilityStatus: ReachabilityStatus {
        
        var zeroAddress = sockaddr_in()
        zeroAddress.sin_len = UInt8(MemoryLayout<sockaddr_in>.size)
        zeroAddress.sin_family = sa_family_t(AF_INET)
        guard let defaultRouteReachability = withUnsafePointer(to: &zeroAddress, {
            $0.withMemoryRebound(to: sockaddr.self, capacity: 1) {
                SCNetworkReachabilityCreateWithAddress(nil, $0)
            }
        }) else {
            return .notReachable
        }
        
        var flags: SCNetworkReachabilityFlags = []
        if !SCNetworkReachabilityGetFlags(defaultRouteReachability, &flags) {
            return .notReachable
        }
        
        if flags.contains(.reachable) == false {
            // The target host is not reachable.
            return .notReachable
        }
        else if flags.contains(.isWWAN) == true {
            // WWAN connections are OK if the calling application is using the CFNetwork APIs.
            return .reachableViaWWAN
        }
        else if flags.contains(.connectionRequired) == false {
            // If the target host is reachable and no connection is required then we'll assume that you're on Wi-Fi...
            return .reachableViaWiFi
        }
        else if (flags.contains(.connectionOnDemand) == true || flags.contains(.connectionOnTraffic) == true) && flags.contains(.interventionRequired) == false {
            // The connection is on-demand (or on-traffic) if the calling application is using the CFSocketStream or higher APIs and no [user] intervention is needed
            return .reachableViaWiFi
        }
        else {
            return .notReachable
        }
    }
}

在任何方法中使用下面的条件

if currentReachabilityStatus == .notReachable {
    // Network Unavailable
} else {
    // Network Available
}

我改进了莱科斯的例子。我添加了一些额外的控件来解决双重触发问题，还添加了通知支持来侦听状态更改。

我为防止双重触发问题而添加的控件还显示了设备主要使用哪个连接源来访问互联网。

例如，即使设备同时连接到蜂窝网络和Wi-Fi，“状态”返回为“connectedViaWiFi”，以指示当前的互联网访问是通过Wi-Fi。

import Foundation
import Network

class Reachability {

    enum StatusFlag {
        case unknow
        case noConnection
        case connectedViaWiFi
        case connectedViaCellular
    }

    static let connectionStatusHasChangedNotification = NSNotification.Name("Reachability.connectionStatusHasChangedNotification")
    static let shared = Reachability()

    private var monitorForWifi: NWPathMonitor?
    private var monitorForCellular: NWPathMonitor?
    private var wifiStatus: NWPath.Status = .requiresConnection
    private var cellularStatus: NWPath.Status = .requiresConnection
    private var ignoreInitialWiFiStatusUpdate: Bool = true
    private var ignoreInitialCelluluarStatusUpdate: Bool = true
    private var isReachableOnCellular: Bool { cellularStatus == .satisfied }
    private var isReachableOnWiFi: Bool { wifiStatus == .satisfied }
    var status: StatusFlag = .unknow {
        didSet {
            guard status != oldValue else { return }
            DispatchQueue.main.async { [weak self] in
                NotificationCenter.default.post(name: Self.connectionStatusHasChangedNotification,
                                                object: self?.status)
            }
        }
    }

    func startMonitoring() {
        monitorForWifi = NWPathMonitor(requiredInterfaceType: .wifi)
        monitorForWifi?.pathUpdateHandler = { [weak self] path in
            self?.wifiStatus = path.status
            self?.ignoreInitialWiFiStatusUpdate = false
            self?.updateStatus()
        }
        monitorForCellular = NWPathMonitor(requiredInterfaceType: .cellular)
        monitorForCellular?.pathUpdateHandler = { [weak self] path in
            self?.cellularStatus = path.status
            self?.ignoreInitialCelluluarStatusUpdate = false
            self?.updateStatus()
        }
        let queue = DispatchQueue.global(qos: .background)
        monitorForCellular?.start(queue: queue)
        monitorForWifi?.start(queue: queue)
    }

    func stopMonitoring() {
        monitorForWifi?.cancel()
        monitorForWifi = nil
        monitorForCellular?.cancel()
        monitorForCellular = nil
        wifiStatus = .requiresConnection
        cellularStatus = .requiresConnection
        status = .unknow
        ignoreInitialWiFiStatusUpdate = true
        ignoreInitialCelluluarStatusUpdate = true
    }

    private func updateStatus() {
        if ignoreInitialWiFiStatusUpdate || ignoreInitialCelluluarStatusUpdate {
            return
        }
        if !(isReachableOnCellular && isReachableOnWiFi) {
            if isReachableOnCellular && !isReachableOnWiFi {
                status = .connectedViaCellular
            } else if isReachableOnWiFi && !isReachableOnCellular {
                status = .connectedViaWiFi
            } else {
                status = .noConnection
            }
        } else {
            status = .connectedViaWiFi
        }
    }

    static func isConnectedToNetwork() -> Bool {
        return shared.isReachableOnCellular || shared.isReachableOnWiFi
    }
}

示例使用

    override func viewDidLoad() {
        super.viewDidLoad()
        NotificationCenter.default.addObserver(self, selector: #selector(reachabilityChanged(_:)), name: Reachability.connectionStatusHasChangedNotification, object: nil)
        Reachability.shared.startMonitoring()
    }

    @objc func reachabilityChanged(_ sender: Notification) {
        guard let statusFlag = sender.object as? Reachability.StatusFlag else { return }
        print("TEST -> statusFlag: \(statusFlag)")
    }

为了解决评论中提到的4G问题，我使用@AshleyMills的可达性实现作为参考，重写了Swift 3.1的可达性:

更新:Xcode 10.1•Swift 4或更高版本

Reachability.swift文件

import Foundation
import SystemConfiguration

class Reachability {
    var hostname: String?
    var isRunning = false
    var isReachableOnWWAN: Bool
    var reachability: SCNetworkReachability?
    var reachabilityFlags = SCNetworkReachabilityFlags()
    let reachabilitySerialQueue = DispatchQueue(label: "ReachabilityQueue")
    init(hostname: String) throws {
        guard let reachability = SCNetworkReachabilityCreateWithName(nil, hostname) else {
            throw Network.Error.failedToCreateWith(hostname)
        }
        self.reachability = reachability
        self.hostname = hostname
        isReachableOnWWAN = true
        try start()
    }
    init() throws {
        var zeroAddress = sockaddr_in()
        zeroAddress.sin_len = UInt8(MemoryLayout<sockaddr_in>.size)
        zeroAddress.sin_family = sa_family_t(AF_INET)
        guard let reachability = withUnsafePointer(to: &zeroAddress, {
            $0.withMemoryRebound(to: sockaddr.self, capacity: 1) {
                SCNetworkReachabilityCreateWithAddress(nil, $0)
            }
        }) else {
            throw Network.Error.failedToInitializeWith(zeroAddress)
        }
        self.reachability = reachability
        isReachableOnWWAN = true
        try start()
    }
    var status: Network.Status {
        return  !isConnectedToNetwork ? .unreachable :
                isReachableViaWiFi    ? .wifi :
                isRunningOnDevice     ? .wwan : .unreachable
    }
    var isRunningOnDevice: Bool = {
        #if targetEnvironment(simulator)
            return false
        #else
            return true
        #endif
    }()
    deinit { stop() }
}

extension Reachability {

    func start() throws {
        guard let reachability = reachability, !isRunning else { return }
        var context = SCNetworkReachabilityContext(version: 0, info: nil, retain: nil, release: nil, copyDescription: nil)
        context.info = Unmanaged<Reachability>.passUnretained(self).toOpaque()
        guard SCNetworkReachabilitySetCallback(reachability, callout, &context) else { stop()
            throw Network.Error.failedToSetCallout
        }
        guard SCNetworkReachabilitySetDispatchQueue(reachability, reachabilitySerialQueue) else { stop()
            throw Network.Error.failedToSetDispatchQueue
        }
        reachabilitySerialQueue.async { self.flagsChanged() }
        isRunning = true
    }

    func stop() {
        defer { isRunning = false }
        guard let reachability = reachability else { return }
        SCNetworkReachabilitySetCallback(reachability, nil, nil)
        SCNetworkReachabilitySetDispatchQueue(reachability, nil)
        self.reachability = nil
    }

    var isConnectedToNetwork: Bool {
        return isReachable &&
               !isConnectionRequiredAndTransientConnection &&
               !(isRunningOnDevice && isWWAN && !isReachableOnWWAN)
    }

    var isReachableViaWiFi: Bool {
        return isReachable && isRunningOnDevice && !isWWAN
    }

    /// Flags that indicate the reachability of a network node name or address, including whether a connection is required, and whether some user intervention might be required when establishing a connection.
    var flags: SCNetworkReachabilityFlags? {
        guard let reachability = reachability else { return nil }
        var flags = SCNetworkReachabilityFlags()
        return withUnsafeMutablePointer(to: &flags) {
            SCNetworkReachabilityGetFlags(reachability, UnsafeMutablePointer($0))
            } ? flags : nil
    }

    /// compares the current flags with the previous flags and if changed posts a flagsChanged notification
    func flagsChanged() {
        guard let flags = flags, flags != reachabilityFlags else { return }
        reachabilityFlags = flags
        NotificationCenter.default.post(name: .flagsChanged, object: self)
    }

    /// The specified node name or address can be reached via a transient connection, such as PPP.
    var transientConnection: Bool { return flags?.contains(.transientConnection) == true }

    /// The specified node name or address can be reached using the current network configuration.
    var isReachable: Bool { return flags?.contains(.reachable) == true }

    /// The specified node name or address can be reached using the current network configuration, but a connection must first be established. If this flag is set, the kSCNetworkReachabilityFlagsConnectionOnTraffic flag, kSCNetworkReachabilityFlagsConnectionOnDemand flag, or kSCNetworkReachabilityFlagsIsWWAN flag is also typically set to indicate the type of connection required. If the user must manually make the connection, the kSCNetworkReachabilityFlagsInterventionRequired flag is also set.
    var connectionRequired: Bool { return flags?.contains(.connectionRequired) == true }

    /// The specified node name or address can be reached using the current network configuration, but a connection must first be established. Any traffic directed to the specified name or address will initiate the connection.
    var connectionOnTraffic: Bool { return flags?.contains(.connectionOnTraffic) == true }

    /// The specified node name or address can be reached using the current network configuration, but a connection must first be established.
    var interventionRequired: Bool { return flags?.contains(.interventionRequired) == true }

    /// The specified node name or address can be reached using the current network configuration, but a connection must first be established. The connection will be established "On Demand" by the CFSocketStream programming interface (see CFStream Socket Additions for information on this). Other functions will not establish the connection.
    var connectionOnDemand: Bool { return flags?.contains(.connectionOnDemand) == true }

    /// The specified node name or address is one that is associated with a network interface on the current system.
    var isLocalAddress: Bool { return flags?.contains(.isLocalAddress) == true }

    /// Network traffic to the specified node name or address will not go through a gateway, but is routed directly to one of the interfaces in the system.
    var isDirect: Bool { return flags?.contains(.isDirect) == true }

    /// The specified node name or address can be reached via a cellular connection, such as EDGE or GPRS.
    var isWWAN: Bool { return flags?.contains(.isWWAN) == true }

    /// The specified node name or address can be reached using the current network configuration, but a connection must first be established. If this flag is set
    /// The specified node name or address can be reached via a transient connection, such as PPP.
    var isConnectionRequiredAndTransientConnection: Bool {
        return (flags?.intersection([.connectionRequired, .transientConnection]) == [.connectionRequired, .transientConnection]) == true
    }
}

func callout(reachability: SCNetworkReachability, flags: SCNetworkReachabilityFlags, info: UnsafeMutableRawPointer?) {
    guard let info = info else { return }
    DispatchQueue.main.async {
        Unmanaged<Reachability>
            .fromOpaque(info)
            .takeUnretainedValue()
            .flagsChanged()
    }
}

extension Notification.Name {
    static let flagsChanged = Notification.Name("FlagsChanged")
}

struct Network {
    static var reachability: Reachability!
    enum Status: String {
        case unreachable, wifi, wwan
    }
    enum Error: Swift.Error {
        case failedToSetCallout
        case failedToSetDispatchQueue
        case failedToCreateWith(String)
        case failedToInitializeWith(sockaddr_in)
    }
}

使用

在你的AppDelegate.swift didFinishLaunchingWithOptions方法中初始化它，并处理任何可能发生的错误:

import UIKit
@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
    var window: UIWindow?
    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        do {
            try Network.reachability = Reachability(hostname: "www.google.com")
        }
        catch {
            switch error as? Network.Error {
            case let .failedToCreateWith(hostname)?:
                print("Network error:\nFailed to create reachability object With host named:", hostname)
            case let .failedToInitializeWith(address)?:
                print("Network error:\nFailed to initialize reachability object With address:", address)
            case .failedToSetCallout?:
                print("Network error:\nFailed to set callout")
            case .failedToSetDispatchQueue?:
                print("Network error:\nFailed to set DispatchQueue")
            case .none:
                print(error)
            }
        }
        return true
    }
}

和一个视图控制器示例:

import UIKit
class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        NotificationCenter.default
            .addObserver(self,
                         selector: #selector(statusManager),
                         name: .flagsChanged,
                         object: nil)
        updateUserInterface()
    }
    func updateUserInterface() {
        switch Network.reachability.status {
        case .unreachable:
            view.backgroundColor = .red
        case .wwan:
            view.backgroundColor = .yellow
        case .wifi:
            view.backgroundColor = .green
        }
        print("Reachability Summary")
        print("Status:", Network.reachability.status)
        print("HostName:", Network.reachability.hostname ?? "nil")
        print("Reachable:", Network.reachability.isReachable)
        print("Wifi:", Network.reachability.isReachableViaWiFi)
    }
    @objc func statusManager(_ notification: Notification) {
        updateUserInterface()
    }
}

示例项目

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

open class Reachability {
    
    class 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)
    }
}

你可以在代码的任何地方调用Reachability，就像

if Reachability.isConnectedToNetwork() {
    print("Network is connected")
} else {
    print("Network is not connected")
}

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。

如果你的项目有一个高于或等于iOS 12的目标，并使用组合，你可以使用这一小段代码。

import Combine
import Network

enum NerworkType {
    case wifi
    case cellular
    case loopBack
    case wired
    case other
}

protocol ReachabilityServiceContract {
    var reachabilityInfos: PassthroughSubject<NWPath, Never> { get set }
    var isNetworkAvailable: CurrentValueSubject<Bool, Never> { get set }
    var typeOfCurrentConnection: PassthroughSubject<NerworkType, Never> { get set }
}

final class ReachabilityService: ReachabilityServiceContract {
    var reachabilityInfos: PassthroughSubject<NWPath, Never> = .init()
    var isNetworkAvailable: CurrentValueSubject<Bool, Never> = .init(false)
    var typeOfCurrentConnection: PassthroughSubject<NerworkType, Never> = .init()

    private let monitor: NWPathMonitor
    private let backgroudQueue = DispatchQueue.global(qos: .background)

    init() {
        monitor = NWPathMonitor()
        setUp()
    }

    init(with interFaceType: NWInterface.InterfaceType) {
        monitor = NWPathMonitor(requiredInterfaceType: interFaceType)
        setUp()
    }

    deinit {
        monitor.cancel()
    }
}

private extension ReachabilityService {
    func setUp() {
    
        monitor.pathUpdateHandler = { [weak self] path in
            self?.reachabilityInfos.send(path)
            switch path.status {
            case .satisfied:
                self?.isNetworkAvailable.send(true)
            case .unsatisfied, .requiresConnection:
                self?.isNetworkAvailable.send(false)
            @unknown default:
                self?.isNetworkAvailable.send(false)
            }
            if path.usesInterfaceType(.wifi) {
                self?.typeOfCurrentConnection.send(.wifi)
            } else if path.usesInterfaceType(.cellular) {
                self?.typeOfCurrentConnection.send(.cellular)
            } else if path.usesInterfaceType(.loopback) {
                self?.typeOfCurrentConnection.send(.loopBack)
            } else if path.usesInterfaceType(.wiredEthernet) {
                self?.typeOfCurrentConnection.send(.wired)
            } else if path.usesInterfaceType(.other) {
                self?.typeOfCurrentConnection.send(.other)
            }
        }
    
        monitor.start(queue: backgroudQueue)
    }
}

只要订阅你想要跟踪的变量，你就会得到任何变化的更新。