Swift 5解决方案:

下载ashleymills的Reachability类 https://github.com/ashleymills/Reachability.swift。 将Reachability类添加到项目中。 将以下代码放入维护连接状态的类中

class ConnectionManager {

    static let shared = ConnectionManager()
    private init () {}

    func hasConnectivity() -> Bool {
        do {
            let reachability: Reachability = try Reachability()
            let networkStatus = reachability.connection
            
            switch networkStatus {
            case .unavailable:
                return false
            case .wifi, .cellular:
                return true
            }
        }
        catch {
            return false
        }
    }
}

像下面这样使用它:

ConnectionManager.shared.hasConnectivity()

这是我自己发现的。

Xcode: 7.3.1, iOS 9.3.3

在我的项目中使用ashleymills/Reachability.swift作为Reachability.swift，我创建了以下函数:

func hasConnectivity() -> Bool {
    do {
        let reachability: Reachability = try Reachability.reachabilityForInternetConnection()
        let networkStatus: Int = reachability.currentReachabilityStatus.hashValue

        return (networkStatus != 0)
    }
    catch {
        // Handle error however you please
        return false
    }
}

只要在需要检查连接的地方调用hasConnectivity()即可。这适用于Wifi和蜂窝网络。

添加ashleyymills的reacbility .swift，这样人们就不必在不同的网站之间切换了:

Copyright (c) 2014, Ashley Mills
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice, this
list of conditions and the following disclaimer.

2. Redistributions in binary form must reproduce the above copyright notice,
this list of conditions and the following disclaimer in the documentation
and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.
*/

// Reachability.swift version 2.2beta2

import SystemConfiguration
import Foundation

public enum ReachabilityError: ErrorType {
    case FailedToCreateWithAddress(sockaddr_in)
    case FailedToCreateWithHostname(String)
    case UnableToSetCallback
    case UnableToSetDispatchQueue
}

public let ReachabilityChangedNotification = "ReachabilityChangedNotification"

func callback(reachability:SCNetworkReachability, flags: SCNetworkReachabilityFlags, info: UnsafeMutablePointer<Void>) {
    let reachability = Unmanaged<Reachability>.fromOpaque(COpaquePointer(info)).takeUnretainedValue()

    dispatch_async(dispatch_get_main_queue()) {
        reachability.reachabilityChanged(flags)
    }
}


public class Reachability: NSObject {

    public typealias NetworkReachable = (Reachability) -> ()
    public typealias NetworkUnreachable = (Reachability) -> ()

    public enum NetworkStatus: CustomStringConvertible {

        case NotReachable, ReachableViaWiFi, ReachableViaWWAN

        public var description: String {
            switch self {
            case .ReachableViaWWAN:
                return "Cellular"
            case .ReachableViaWiFi:
                return "WiFi"
            case .NotReachable:
                return "No Connection"
            }
        }
    }

    // MARK: - *** Public properties ***
    public var whenReachable: NetworkReachable?
    public var whenUnreachable: NetworkUnreachable?
    public var reachableOnWWAN: Bool
    public var notificationCenter = NSNotificationCenter.defaultCenter()

    public var currentReachabilityStatus: NetworkStatus {
        if isReachable() {
            if isReachableViaWiFi() {
                return .ReachableViaWiFi
            }
            if isRunningOnDevice {
                return .ReachableViaWWAN
            }
        }
        return .NotReachable
    }

    public var currentReachabilityString: String {
        return "\(currentReachabilityStatus)"
    }

    private var previousFlags: SCNetworkReachabilityFlags?

    // MARK: - *** Initialisation methods ***

    required public init(reachabilityRef: SCNetworkReachability) {
        reachableOnWWAN = true
        self.reachabilityRef = reachabilityRef
    }

    public convenience init(hostname: String) throws {

        let nodename = (hostname as NSString).UTF8String
        guard let ref = SCNetworkReachabilityCreateWithName(nil, nodename) else { throw ReachabilityError.FailedToCreateWithHostname(hostname) }

        self.init(reachabilityRef: ref)
    }

    public class func reachabilityForInternetConnection() throws -> Reachability {

        var zeroAddress = sockaddr_in()
        zeroAddress.sin_len = UInt8(sizeofValue(zeroAddress))
        zeroAddress.sin_family = sa_family_t(AF_INET)

        guard let ref = withUnsafePointer(&zeroAddress, {
            SCNetworkReachabilityCreateWithAddress(nil, UnsafePointer($0))
        }) else { throw ReachabilityError.FailedToCreateWithAddress(zeroAddress) }

        return Reachability(reachabilityRef: ref)
    }

    public class func reachabilityForLocalWiFi() throws -> Reachability {

        var localWifiAddress: sockaddr_in = sockaddr_in(sin_len: __uint8_t(0), sin_family: sa_family_t(0), sin_port: in_port_t(0), sin_addr: in_addr(s_addr: 0), sin_zero: (0, 0, 0, 0, 0, 0, 0, 0))
        localWifiAddress.sin_len = UInt8(sizeofValue(localWifiAddress))
        localWifiAddress.sin_family = sa_family_t(AF_INET)

        // IN_LINKLOCALNETNUM is defined in <netinet/in.h> as 169.254.0.0
        let address: UInt32 = 0xA9FE0000
        localWifiAddress.sin_addr.s_addr = in_addr_t(address.bigEndian)

        guard let ref = withUnsafePointer(&localWifiAddress, {
            SCNetworkReachabilityCreateWithAddress(nil, UnsafePointer($0))
        }) else { throw ReachabilityError.FailedToCreateWithAddress(localWifiAddress) }

        return Reachability(reachabilityRef: ref)
    }

    // MARK: - *** Notifier methods ***
    public func startNotifier() throws {

        guard !notifierRunning else { return }

        var context = SCNetworkReachabilityContext(version: 0, info: nil, retain: nil, release: nil, copyDescription: nil)
        context.info = UnsafeMutablePointer(Unmanaged.passUnretained(self).toOpaque())

        if !SCNetworkReachabilitySetCallback(reachabilityRef!, callback, &context) {
            stopNotifier()
            throw ReachabilityError.UnableToSetCallback
        }

        if !SCNetworkReachabilitySetDispatchQueue(reachabilityRef!, reachabilitySerialQueue) {
            stopNotifier()
            throw ReachabilityError.UnableToSetDispatchQueue
        }

        // Perform an intial check
        dispatch_async(reachabilitySerialQueue) { () -> Void in
            let flags = self.reachabilityFlags
            self.reachabilityChanged(flags)
        }

        notifierRunning = true
    }

    public func stopNotifier() {
        defer { notifierRunning = false }
        guard let reachabilityRef = reachabilityRef else { return }

        SCNetworkReachabilitySetCallback(reachabilityRef, nil, nil)
        SCNetworkReachabilitySetDispatchQueue(reachabilityRef, nil)
    }

    // MARK: - *** Connection test methods ***
    public func isReachable() -> Bool {
        let flags = reachabilityFlags
        return isReachableWithFlags(flags)
    }

    public func isReachableViaWWAN() -> Bool {

        let flags = reachabilityFlags

        // Check we're not on the simulator, we're REACHABLE and check we're on WWAN
        return isRunningOnDevice && isReachable(flags) && isOnWWAN(flags)
    }

    public func isReachableViaWiFi() -> Bool {

        let flags = reachabilityFlags

        // Check we're reachable
        if !isReachable(flags) {
            return false
        }

        // Must be on WiFi if reachable but not on an iOS device (i.e. simulator)
        if !isRunningOnDevice {
            return true
        }

        // Check we're NOT on WWAN
        return !isOnWWAN(flags)
    }

    // MARK: - *** Private methods ***
    private var isRunningOnDevice: Bool = {
        #if (arch(i386) || arch(x86_64)) && os(iOS)
            return false
        #else
            return true
        #endif
    }()

    private var notifierRunning = false
    private var reachabilityRef: SCNetworkReachability?
    private let reachabilitySerialQueue = dispatch_queue_create("uk.co.ashleymills.reachability", DISPATCH_QUEUE_SERIAL)

    private func reachabilityChanged(flags: SCNetworkReachabilityFlags) {

        guard previousFlags != flags else { return }

        if isReachableWithFlags(flags) {
            if let block = whenReachable {
                block(self)
            }
        } else {
            if let block = whenUnreachable {
                block(self)
            }
        }

        notificationCenter.postNotificationName(ReachabilityChangedNotification, object:self)

        previousFlags = flags
    }

    private func isReachableWithFlags(flags: SCNetworkReachabilityFlags) -> Bool {

        if !isReachable(flags) {
            return false
        }

        if isConnectionRequiredOrTransient(flags) {
            return false
        }

        if isRunningOnDevice {
            if isOnWWAN(flags) && !reachableOnWWAN {
                // We don't want to connect when on 3G.
                return false
            }
        }

        return true
    }

    // WWAN may be available, but not active until a connection has been established.
    // WiFi may require a connection for VPN on Demand.
    private func isConnectionRequired() -> Bool {
        return connectionRequired()
    }

    private func connectionRequired() -> Bool {
        let flags = reachabilityFlags
        return isConnectionRequired(flags)
    }

    // Dynamic, on demand connection?
    private func isConnectionOnDemand() -> Bool {
        let flags = reachabilityFlags
        return isConnectionRequired(flags) && isConnectionOnTrafficOrDemand(flags)
    }

    // Is user intervention required?
    private func isInterventionRequired() -> Bool {
        let flags = reachabilityFlags
        return isConnectionRequired(flags) && isInterventionRequired(flags)
    }

    private func isOnWWAN(flags: SCNetworkReachabilityFlags) -> Bool {
        #if os(iOS)
            return flags.contains(.IsWWAN)
        #else
            return false
        #endif
    }
    private func isReachable(flags: SCNetworkReachabilityFlags) -> Bool {
        return flags.contains(.Reachable)
    }
    private func isConnectionRequired(flags: SCNetworkReachabilityFlags) -> Bool {
        return flags.contains(.ConnectionRequired)
    }
    private func isInterventionRequired(flags: SCNetworkReachabilityFlags) -> Bool {
        return flags.contains(.InterventionRequired)
    }
    private func isConnectionOnTraffic(flags: SCNetworkReachabilityFlags) -> Bool {
        return flags.contains(.ConnectionOnTraffic)
    }
    private func isConnectionOnDemand(flags: SCNetworkReachabilityFlags) -> Bool {
        return flags.contains(.ConnectionOnDemand)
    }
    func isConnectionOnTrafficOrDemand(flags: SCNetworkReachabilityFlags) -> Bool {
        return !flags.intersect([.ConnectionOnTraffic, .ConnectionOnDemand]).isEmpty
    }
    private func isTransientConnection(flags: SCNetworkReachabilityFlags) -> Bool {
        return flags.contains(.TransientConnection)
    }
    private func isLocalAddress(flags: SCNetworkReachabilityFlags) -> Bool {
        return flags.contains(.IsLocalAddress)
    }
    private func isDirect(flags: SCNetworkReachabilityFlags) -> Bool {
        return flags.contains(.IsDirect)
    }
    private func isConnectionRequiredOrTransient(flags: SCNetworkReachabilityFlags) -> Bool {
        let testcase:SCNetworkReachabilityFlags = [.ConnectionRequired, .TransientConnection]
        return flags.intersect(testcase) == testcase
    }

    private var reachabilityFlags: SCNetworkReachabilityFlags {

        guard let reachabilityRef = reachabilityRef else { return SCNetworkReachabilityFlags() }

        var flags = SCNetworkReachabilityFlags()
        let gotFlags = withUnsafeMutablePointer(&flags) {
            SCNetworkReachabilityGetFlags(reachabilityRef, UnsafeMutablePointer($0))
        }

        if gotFlags {
            return flags
        } else {
            return SCNetworkReachabilityFlags()
        }
    }

    override public var description: String {

        var W: String
        if isRunningOnDevice {
            W = isOnWWAN(reachabilityFlags) ? "W" : "-"
        } else {
            W = "X"
        }
        let R = isReachable(reachabilityFlags) ? "R" : "-"
        let c = isConnectionRequired(reachabilityFlags) ? "c" : "-"
        let t = isTransientConnection(reachabilityFlags) ? "t" : "-"
        let i = isInterventionRequired(reachabilityFlags) ? "i" : "-"
        let C = isConnectionOnTraffic(reachabilityFlags) ? "C" : "-"
        let D = isConnectionOnDemand(reachabilityFlags) ? "D" : "-"
        let l = isLocalAddress(reachabilityFlags) ? "l" : "-"
        let d = isDirect(reachabilityFlags) ? "d" : "-"

        return "\(W)\(R) \(c)\(t)\(i)\(C)\(D)\(l)\(d)"
    }

    deinit {
        stopNotifier()

        reachabilityRef = nil
        whenReachable = nil
        whenUnreachable = nil
    }
}

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!")
}

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
}

虽然它可能不能直接确定手机是否连接到网络，但最简单的解决方案是“ping”谷歌或其他服务器(除非手机连接到网络，否则这是不可能的):

private var urlSession:URLSession = {
    var newConfiguration:URLSessionConfiguration = .default
    newConfiguration.waitsForConnectivity = false
    newConfiguration.allowsCellularAccess = true
    return URLSession(configuration: newConfiguration)
}()

public func canReachGoogle() -> Bool
{
    let url = URL(string: "https://8.8.8.8")
    let semaphore = DispatchSemaphore(value: 0)
    var success = false
    let task = urlSession.dataTask(with: url!)
    { data, response, error in
        if error != nil
        {
            success = false
        }
        else
        {
            success = true
        }
        semaphore.signal()
    }

    task.resume()
    semaphore.wait()

    return success
}

如果您担心服务器可能宕机或阻塞您的IP，您总是可以以类似的方式ping多个服务器，并返回它们中的任何一个是否可达。或者让别人专门为这个目的设置一个专用服务器。

在以下代码的帮助下，您可以检查网络连接的蜂窝网络以及wifi。 Swift 3.0

import UIKit
import Foundation
import SystemConfiguration

class NetworkConnection: UIViewController {

  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)

    guard let defaultRouteReachability = withUnsafePointer(to: &zeroAddress, {
      $0.withMemoryRebound(to: sockaddr.self, capacity: 1) {
        SCNetworkReachabilityCreateWithAddress(nil, $0)
      }
    }) else {
      return false
    }

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

  class func checkConnection(sender:UIViewController){
    if NetworkConnection.isConnectedToNetwork() == true {
      print("Connected to the internet")
      //  Do something
    } else {
      print("No internet connection")
      let alertController = UIAlertController(title: "No Internet Available", message: "", preferredStyle: UIAlertControllerStyle.alert)
      let okAction = UIAlertAction(title: "Ok", style: UIAlertActionStyle.default){(result:UIAlertAction) -> Void in
        return
      }
      alertController.addAction(okAction)
      sender.present(alertController, animated: true, completion: nil)
      //  Do something
    }
  }

}