在开发中，有时候我们需要获取这些信息：
手机是否联网
当前网络是WiFi还是蜂窝
那么我总结一下具体的使用场景有哪些？肯定有遗漏：
聊天列表，需要实时监控当前的网络是不是可达的，如果不可达，则出现不能联网的提示
在线视屏播放，需要判断当前的网络状态，如果不是WiFi，应该给出流量播放的提示
对于比较重要的网络请求，在请求出错的情况下，判断网路状态，找出请求失败原因。
可以把请求进行缓存后，当监听到网络连接成功后发送。举个例子，每次进app都要把位置信息发给服务器，如果发送失败后，发现是网络不可达造成的失败，那么可以把这个请求放入到一个队列中，在网络可达的时候，开启队列任务。
当网络状态变化时，实时的给用户提示信息
获取某个节点或地址是不是可达的
但是，极其不建议在发请求前，先检测当前的网络是不是可达。因为手机的网络状态是经常变化
SCNetworkReachabilityFlags
SCNetworkReachabilityFlags是获取网络状态最核心的东西。我们来看看它有哪些内容：
作用
SCNetworkReachabilityFlags能够判断某个指定的网络节点名称或者地址是不是可达的，也能判断该节点或地址是不是需要先建立连接，也可以判断是不是需要用户手动去建立连接。
注意：这里所说的连接分为用编程手段连接和用手动建立连接两种
我们只列举出跟本类相关的一些选项：
(1)kSCNetworkReachabilityFlagsReachable 表明当前指定的节点或地址是可达的。注意：可达不是代表节点或地址接受到了数据，而是代表数据能够离开本地,因此。就算是可达的，也不一定能够发送成功
(2)kSCNetworkReachabilityFlagsConnectionRequired 表明要想和指定的节点或地址通信，需要先建立连接。比如说拨号上网。注意：对于手机来说，如果没有返回该标记，就说明手机正在使用蜂窝网路或者WiFi
(3)kSCNetworkReachabilityFlagsConnectionOnTraffic 表明要想和指定的节点或地址通信，必须先建立连接，但是在当前的网络配置下，目标是可达的。注意：任何连接到指定的节点或地址的请求都会触发该标记，举个例子，在很多地方需要输入手机，获取验证码后才能联网，就是这个原理
(4)kSCNetworkReachabilityFlagsConnectionOnDemand 表明要想和指定的节点或地址通信，必须先建立连接，但是在当前的网络配置下，目标是可达的。但是建立连接必须通过CFSocketStream APIs才行，其他的APIs不能建立连接
(5)kSCNetworkReachabilityFlagsInterventionRequired 表明要想和指定的节点或地址通信，必须先建立连接，但是在当前的网络配置下，目标是可达的。需要用户手动提供一些数据，比如密码或者token
(6)kSCNetworkReachabilityFlagsIsWWAN 表明是不是通过蜂窝网络连接
上边的这些选项，会在下边的一个核心方法中使用到，我们在下边的代码中在给出说明。
ConnectionType
/// Defines the various connection types detected by reachability flags.
///
/// - ethernetOrWiFi: The connection type is either over Ethernet or WiFi.
/// - wwan: The connection type is a WWAN connection.
public enum ConnectionType {
case ethernetOrWiFi
case wwan
}
对于手机而言，我们需要的连接类型就两种，一种是蜂窝网络，另一种是WiFi网络。因此在设计NetworkReachabilityManager的时候，通过上边的枚举获取当前的网络连接类型。
NetworkReachabilityStatus
/// Defines the various states of network reachability.
///
/// - unknown: It is unknown whether the network is reachable.
/// - notReachable: The network is not reachable.
/// - reachable: The network is reachable.
public enum NetworkReachabilityStatus {
case unknown
case notReachable
case reachable(ConnectionType)
}
网络状态明显要比网络类型范围更大，因此又增加了两个选项，一个表示当前的网络是未知的，另一个表示当前的网路不可达。
综上所述，我们的目的就是拿到这个NetworkReachabilityStatus，那么NetworkReachabilityManager是如何把NetworkReachabilityStatus传递出来的呢？ 答案就是闭包，
/// A closure executed when the network reachability status changes. The closure takes a single argument: the
/// network reachability status.
public typealias Listener = (NetworkReachabilityStatus) -> Void
swift的闭包，我们已经很熟悉了，在开发中，首先初始化NetworkReachabilityManager，然后设置Listener，第三部开启监控，这个开启监控的方法会在下边讲到。
Properties
在NetworkReachabilityManager中，属性分为public和private，我们先看public部分：
/// Whether the network is currently reachable.
public var isReachable: Bool { return isReachableOnWWAN || isReachableOnEthernetOrWiFi }
/// Whether the network is currently reachable over the WWAN interface.
public var isReachableOnWWAN: Bool { return networkReachabilityStatus == .reachable(.wwan) }
/// Whether the network is currently reachable over Ethernet or WiFi interface.
public var isReachableOnEthernetOrWiFi: Bool { return networkReachabilityStatus == .reachable(.ethernetOrWiFi) }
/// The current network reachability status.
public var networkReachabilityStatus: NetworkReachabilityStatus {
guard let flags = self.flags else { return .unknown }
return networkReachabilityStatusForFlags(flags)
}
/// The dispatch queue to execute the `listener` closure on.
public var listenerQueue: DispatchQueue = DispatchQueue.main
/// A closure executed when the network reachability status changes.
public var listener: Listener?
public表明我们可以通过NetworkReachabilityManager实例直接获得的属性，能够让我们很方便的获取我们想要的数据。我们对这些属性做一些简单的说明：
(1)isReachable: Bool 当前网络是可达的，要么是蜂窝网络，要么是WiFi连接
(2)isReachableOnWWAN: Bool 表明当前网络是通过蜂窝网络连接
(3)isReachableOnEthernetOrWiFi: Bool 表明当前网络是通过WiFi连接
(4)networkReachabilityStatus: NetworkReachabilityStatus 返回当前的网络状态，这也是上边3个判断的基础
(5)listenerQueue 监听listener在那个队列中调用，默认的是主队列
listener: Listener 监听闭包，当网络状态发生变化时会调用
上边这些public属性有的是只读的，有的不是，我们在看看private属性：
(6)flags: SCNetworkReachabilityFlags? 主要目的是获取flags，在上边我们介绍过，网络状态就是根据flags判断出来的是通过下边的方法获取到的：
@available(iOS 2.0, *)
public func SCNetworkReachabilityGetFlags(_ target: SCNetworkReachability, _ flags: UnsafeMutablePointer<SCNetworkReachabilityFlags>) -> Bool
(7)reachability: SCNetworkReachability 必不可少的对象，有了它才能获取flags
(8)previousFlags: SCNetworkReachabilityFlags 用于记录当前的flags，在收到系统的callBack方法后，通过比较现在的flags和previousFlags来判断是不是要调用listener函数
Initialization
关于初始化，NetworkReachabilityManager提供了三种选择：
通过指定host
/// Creates a `NetworkReachabilityManager` instance with the specified host.
///
/// - parameter host: The host used to evaluate network reachability.
///
/// - returns: The new `NetworkReachabilityManager` instance.
public convenience init?(host: String) {
guard let reachability = SCNetworkReachabilityCreateWithName(nil, host) else { return nil }
self.init(reachability: reachability)
}
通过init方法会默认的设置为指向0.0.0.0
/// Creates a `NetworkReachabilityManager` instance that monitors the address 0.0.0.0.
///
/// Reachability treats the 0.0.0.0 address as a special token that causes it to monitor the general routing
/// status of the device, both IPv4 and IPv6.
///
/// - returns: The new `NetworkReachabilityManager` instance.
public convenience init?() {
var address = sockaddr_in()
address.sin_len = UInt8(MemoryLayout<sockaddr_in>.size)
address.sin_family = sa_family_t(AF_INET)
guard let reachability = withUnsafePointer(to: &address, { pointer in
return pointer.withMemoryRebound(to: sockaddr.self, capacity: MemoryLayout<sockaddr>.size) {
return SCNetworkReachabilityCreateWithAddress(nil, $0)
}
}) else { return nil }
self.init(reachability: reachability)
}
通过指定SCNetworkReachability
private init(reachability: SCNetworkReachability) {
self.reachability = reachability
self.previousFlags = SCNetworkReachabilityFlags()
}
deinit
deinit {
stopListening()
}
上边的代码表明，在NetworkReachabilityManager被销毁的时候，会停止监控，因此在开发中就要额外注意这一点，最好让控制器强引用它。
startListening
在开发中，对于开发某个功能，我有时候会称为开发某种能力类，我们可以采取自上而下的方法，我先定义出最基本的伪代码，对于网络监控我们的伪代码就应该是下边这样的
(1)创建一个监控者
(2)设置监控回调事件
(3)开始监控
(4)停止监控
在这里讲点额外的编程技巧，上边的4个伪代码我们可以成为子程序，每个子程序都应该有一定的内聚性要求，就是说每个子程序最好能够实现一个单一的功能。子程序会出现成对出现的情况，比如开始和停止，等等。那么我们现在要讲的就是第三步，开始监控。
@discardableResult
public func startListening() -> Bool {
var context = SCNetworkReachabilityContext(version: 0, info: nil, retain: nil, release: nil, copyDescription: nil)
context.info = Unmanaged.passUnretained(self).toOpaque()
let callbackEnabled = SCNetworkReachabilitySetCallback(
reachability,
{ (_, flags, info) in
let reachability = Unmanaged<NetworkReachabilityManager>.fromOpaque(info!).takeUnretainedValue()
reachability.notifyListener(flags)
},
&context
)
let queueEnabled = SCNetworkReachabilitySetDispatchQueue(reachability, listenerQueue)
listenerQueue.async {
self.previousFlags = SCNetworkReachabilityFlags()
self.notifyListener(self.flags ?? SCNetworkReachabilityFlags())
}
return callbackEnabled && queueEnabled
}
@discardableResult表明可以忽略返回值。其实开始监控网络状态就分为两部：
(1)设置Callback回调函数
(2)设置Callback回调队列
当然必要的前提是必须初始化了一个reachability。
这里有一些很有意思的东西，可能我们在swift中是不常见的。比如：Unmanaged.passUnretained(self).toOpaque(),比如:let reachability = Unmanaged<NetworkReachabilityManager>.fromOpaque(info!).takeUnretainedValue()
/// A type for propagating an unmanaged object reference.
///
/// When you use this type, you become partially responsible for
/// keeping the object alive.
public struct Unmanaged<Instance : AnyObject> {
/// Unsafely turns an opaque C pointer into an unmanaged class reference.
///
/// This operation does not change reference counts.
///
/// let str: CFString = Unmanaged.fromOpaque(ptr).takeUnretainedValue()
///
/// - Parameter value: An opaque C pointer.
/// - Returns: An unmanaged class reference to `value`.
public static func fromOpaque(_ value: UnsafeRawPointer) -> Unmanaged<Instance>
/// Unsafely converts an unmanaged class reference to a pointer.
///
/// This operation does not change reference counts.
///
/// let str0: CFString = "boxcar"
/// let bits = Unmanaged.passUnretained(str0)
/// let ptr = bits.toOpaque()
///
/// - Returns: An opaque pointer to the value of this unmanaged reference.
public func toOpaque() -> UnsafeMutableRawPointer
/// Creates an unmanaged reference with an unbalanced retain.
///
/// The instance passed as `value` will leak if nothing eventually balances
/// the retain.
///
/// This is useful when passing an object to an API which Swift does not know
/// the ownership rules for, but you know that the API expects you to pass
/// the object at +1.
///
/// - Parameter value: A class instance.
/// - Returns: An unmanaged reference to the object passed as `value`.
public static func passRetained(_ value: Instance) -> Unmanaged<Instance>
/// Creates an unmanaged reference without performing an unbalanced
/// retain.
///
/// This is useful when passing a reference to an API which Swift
/// does not know the ownership rules for, but you know that the
/// API expects you to pass the object at +0.
///
/// CFArraySetValueAtIndex(.passUnretained(array), i,
/// .passUnretained(object))
///
/// - Parameter value: A class instance.
/// - Returns: An unmanaged reference to the object passed as `value`.
public static func passUnretained(_ value: Instance) -> Unmanaged<Instance>
/// Gets the value of this unmanaged reference as a managed
/// reference without consuming an unbalanced retain of it.
///
/// This is useful when a function returns an unmanaged reference
/// and you know that you're not responsible for releasing the result.
///
/// - Returns: The object referenced by this `Unmanaged` instance.
public func takeUnretainedValue() -> Instance
/// Gets the value of this unmanaged reference as a managed
/// reference and consumes an unbalanced retain of it.
///
/// This is useful when a function returns an unmanaged reference
/// and you know that you're responsible for releasing the result.
///
/// - Returns: The object referenced by this `Unmanaged` instance.
public func takeRetainedValue() -> Instance
/// Performs an unbalanced retain of the object.
public func retain() -> Unmanaged<Instance>
/// Performs an unbalanced release of the object.
public func release()
/// Performs an unbalanced autorelease of the object.
public func autorelease() -> Unmanaged<Instance>
}
这里提供一个文章地址[HandyJSON] 设计思路简析,关于swift中指针的使用可以参考这篇文章。很强大啊。
在上边的开始监控中有一个函数：notifyListener
，这个函数的目的就是通知监听者，也就是触发回调函数。
func notifyListener(_ flags: SCNetworkReachabilityFlags) {
guard previousFlags != flags else { return }
previousFlags = flags
listener?(networkReachabilityStatusForFlags(flags))
}
networkReachabilityStatusForFlags
这个函数是根据flags获取状态的核心函数，但是我觉得没什么好说的，在开发中用的也不多，我们把代码粘一下，然后重点来说说swift中运算符==重载
func networkReachabilityStatusForFlags(_ flags: SCNetworkReachabilityFlags) -> NetworkReachabilityStatus {
/// 这里的contains函数要传递的值是OptionSet自身，因此.reachable换成SCNetworkReachabilityFlags.reachable也是可以的,reachable是一个静态方法
/// flags.contains(.reachable)如果是true，就代表有网络连接
guard flags.contains(.reachable) else { return .notReachable }
var networkStatus: NetworkReachabilityStatus = .notReachable
if !flags.contains(.connectionRequired) { networkStatus = .reachable(.ethernetOrWiFi) }
if flags.contains(.connectionOnDemand) || flags.contains(.connectionOnTraffic) {
if !flags.contains(.interventionRequired) { networkStatus = .reachable(.ethernetOrWiFi) }
}
#if os(iOS)
if flags.contains(.isWWAN) { networkStatus = .reachable(.wwan) }
#endif
return networkStatus
}
运算符重载
要想重载==,需要实现Equatable协议：
public protocol Equatable {
/// Returns a Boolean value indicating whether two values are equal.
///
/// Equality is the inverse of inequality. For any values `a` and `b`,
/// `a == b` implies that `a != b` is `false`.
///
/// - Parameters:
/// - lhs: A value to compare.
/// - rhs: Another value to compare.
public static func ==(lhs: Self, rhs: Self) -> Bool
}
其实，这种思想还是很重要的，在开发中可以通过这种方式来判断两个模型是不是相同，等等很多种使用场景。我简单的把Apple文档中的注释说明部分翻译一下。
==和!=是对立统一的关系，我们自定义了==,同理，!=也就支持了。在swift中，很多基本的数据类型都支持了Equatable协议。
Equatable协议的一个典型的应用场景就是判断一个集合中是否包含某个值。在swift中，如果集合中的值都实现了Equatable协议，那么就可以通过contains(:)方法来判断是不是包含该值。这也说明了contains(:)内部实现应该是通过==来实现的。使用contains(_:)方法的好处就是省去了我们遍历数据，然后再进行判断的繁琐步骤。我们看个例子：
/// let students = ["Nora", "Fern", "Ryan", "Rainer"]
///
/// let nameToCheck = "Ryan"
/// if students.contains(nameToCheck) {
/// print("\(nameToCheck) is signed up!")
/// } else {
/// print("No record of \(nameToCheck).")
/// }
/// // Prints "Ryan is signed up!"
需要把==声明成为自定义类型的静态方法
假如说我们有一个街道地址的结构体：
/// struct StreetAddress {
/// let number: String
/// let street: String
/// let unit: String?
///
/// init(_ number: String, _ street: String, unit: String? = nil) {
/// self.number = number
/// self.street = street
/// self.unit = unit
/// }
/// }
我们让StreetAddress实现Equatable协议：
///
/// extension StreetAddress: Equatable {
/// static func == (lhs: StreetAddress, rhs: StreetAddress) -> Bool {
/// return
/// lhs.number == rhs.number &&
/// lhs.street == rhs.street &&
/// lhs.unit == rhs.unit
/// }
/// }
///
接下来我们就能使用系统的contains(_:)方法来判断一个集合中是不是包含摸个街道地址了。
///
/// let addresses = [StreetAddress("1490", "Grove Street"),
/// StreetAddress("2119", "Maple Avenue"),
/// StreetAddress("1400", "16th Street")]
/// let home = StreetAddress("1400", "16th Street")
///
/// print(addresses[0] == home)
/// // Prints "false"
/// print(addresses.contains(home))
/// // Prints "true"
///
有了上边的知识，我们在看看NetworkReachabilityManager是怎么用的：
extension NetworkReachabilityManager.NetworkReachabilityStatus: Equatable {}
/// Returns whether the two network reachability status values are equal.
///
/// - parameter lhs: The left-hand side value to compare.
/// - parameter rhs: The right-hand side value to compare.
///
/// - returns: `true` if the two values are equal, `false` otherwise.
public func ==(
lhs: NetworkReachabilityManager.NetworkReachabilityStatus,
rhs: NetworkReachabilityManager.NetworkReachabilityStatus)
-> Bool
{
switch (lhs, rhs) {
case (.unknown, .unknown):
return true
case (.notReachable, .notReachable):
return true
case let (.reachable(lhsConnectionType), .reachable(rhsConnectionType)):
return lhsConnectionType == rhsConnectionType
default:
return false
}
}
在swift中，static函数还可以像上边这么用，把函数写到类的代码块之外，当然，上边的代码也可以这么写：
extension NetworkReachabilityManager.NetworkReachabilityStatus: Equatable {
public static func ==(
lhs: NetworkReachabilityManager.NetworkReachabilityStatus,
rhs: NetworkReachabilityManager.NetworkReachabilityStatus)
-> Bool
{
switch (lhs, rhs) {
case (.unknown, .unknown):
return true
case (.notReachable, .notReachable):
return true
case let (.reachable(lhsConnectionType), .reachable(rhsConnectionType)):
return lhsConnectionType == rhsConnectionType
default:
return false
}
}
}
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