Swift 中是否有一个代理可以让我的类(class)知道何时通过计算机的 USB 插入了新设备？我想知道我的程序何时可以使用新设备。

最佳答案

Eric Aya 的回答已经很不错了，但这是 Swift 3 的改编版。我将大部分丑陋的东西包装在一个 USBWatcher 类中；将自己设置为该对象的代表以接收通知。

您可以将以下内容复制/粘贴到 playground 中以查看其工作情况——该示例只是在设备连接/断开连接时向控制台记录一条消息。

不幸的是，IOKit API 没有像其他一些 C API(例如 CoreGraphics)一样得到同样的 Swift 化处理。 io_name_t 是一个笨重的元组而不是一个合适的结构，C 结构通常被导入到 Swift 中； io_object_t 不是真正的引用类型，因此它不能利用 ARC。也许在未来这会改变——如果你想看到更好的 Swift API，你应该 file an enhancement request .

import Foundation
import IOKit
import IOKit.usb

public protocol USBWatcherDelegate: class {
    /// Called on the main thread when a device is connected.
    func deviceAdded(_ device: io_object_t)

    /// Called on the main thread when a device is disconnected.
    func deviceRemoved(_ device: io_object_t)
}

/// An object which observes USB devices added and removed from the system.
/// Abstracts away most of the ugliness of IOKit APIs.
public class USBWatcher {
    private weak var delegate: USBWatcherDelegate?
    private let notificationPort = IONotificationPortCreate(kIOMasterPortDefault)
    private var addedIterator: io_iterator_t = 0
    private var removedIterator: io_iterator_t = 0

    public init(delegate: USBWatcherDelegate) {
        self.delegate = delegate

        func handleNotification(instance: UnsafeMutableRawPointer?, _ iterator: io_iterator_t) {
            let watcher = Unmanaged<USBWatcher>.fromOpaque(instance!).takeUnretainedValue()
            let handler: ((io_iterator_t) -> Void)?
            switch iterator {
            case watcher.addedIterator: handler = watcher.delegate?.deviceAdded
            case watcher.removedIterator: handler = watcher.delegate?.deviceRemoved
            default: assertionFailure("received unexpected IOIterator"); return
            }
            while case let device = IOIteratorNext(iterator), device != IO_OBJECT_NULL {
                handler?(device)
                IOObjectRelease(device)
            }
        }

        let query = IOServiceMatching(kIOUSBDeviceClassName)
        let opaqueSelf = Unmanaged.passUnretained(self).toOpaque()

        // Watch for connected devices.
        IOServiceAddMatchingNotification(
            notificationPort, kIOMatchedNotification, query,
            handleNotification, opaqueSelf, &addedIterator)

        handleNotification(instance: opaqueSelf, addedIterator)

        // Watch for disconnected devices.
        IOServiceAddMatchingNotification(
            notificationPort, kIOTerminatedNotification, query,
            handleNotification, opaqueSelf, &removedIterator)

        handleNotification(instance: opaqueSelf, removedIterator)

        // Add the notification to the main run loop to receive future updates.
        CFRunLoopAddSource(
            CFRunLoopGetMain(),
            IONotificationPortGetRunLoopSource(notificationPort).takeUnretainedValue(),
            .commonModes)
    }

    deinit {
        IOObjectRelease(addedIterator)
        IOObjectRelease(removedIterator)
        IONotificationPortDestroy(notificationPort)
    }
}

extension io_object_t {
    /// - Returns: The device's name.
    func name() -> String? {
        let buf = UnsafeMutablePointer<io_name_t>.allocate(capacity: 1)
        defer { buf.deallocate(capacity: 1) }
        return buf.withMemoryRebound(to: CChar.self, capacity: MemoryLayout<io_name_t>.size) {
            if IORegistryEntryGetName(self, $0) == KERN_SUCCESS {
                return String(cString: $0)
            }
            return nil
        }
    }
}


import PlaygroundSupport
PlaygroundPage.current.needsIndefiniteExecution = true

class Example: USBWatcherDelegate {
    private var usbWatcher: USBWatcher!
    init() {
        usbWatcher = USBWatcher(delegate: self)
    }

    func deviceAdded(_ device: io_object_t) {
        print("device added: \(device.name() ?? "<unknown>")")
    }

    func deviceRemoved(_ device: io_object_t) {
        print("device removed: \(device.name() ?? "<unknown>")")
    }
}

let example = Example()

关于swift - Swift 上的 USB 连接委托(delegate)，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/39003986/