How to implement IOServiceMatchingCallBack in Swift

Question

I would like to detect a specific USB is plugged in/removed in my application. For now, I can get the deviceName with this tutorial Working With USB Device Interfaces. But,

Answer 1

It works after I put the callback function out the class. However, I don't know why.

class IODetection {
    class func monitorUSBEvent(VendorID: Int, ProductID: Int) {


        var portIterator: io_iterator_t = 0
        var kr: kern_return_t = KERN_FAILURE
        let matchingDict = IOServiceMatching(kIOUSBDeviceClassName)

        // Add the VENDOR and PRODUCT IDs to the matching dictionary.
        let vendorIDString = kUSBVendorID as CFStringRef!
        let productIDString = kUSBProductID as CFStringRef!
        CFDictionarySetValue(matchingDict, unsafeAddressOf(vendorIDString), unsafeAddressOf(VendorID))
        CFDictionarySetValue(matchingDict, unsafeAddressOf(productIDString), unsafeAddressOf(ProductID))

        // To set up asynchronous notifications, create a notification port and add its run loop event source to the program’s run loop
        let gNotifyPort: IONotificationPortRef = IONotificationPortCreate(kIOMasterPortDefault)
        let runLoopSource: Unmanaged! = IONotificationPortGetRunLoopSource(gNotifyPort)
        let gRunLoop: CFRunLoop! = CFRunLoopGetCurrent()

        CFRunLoopAddSource(gRunLoop, runLoopSource.takeRetainedValue(), kCFRunLoopDefaultMode)

        // MARK: - USB in Notification
        let observer = UnsafeMutablePointer(unsafeAddressOf(self))
        kr = IOServiceAddMatchingNotification(gNotifyPort,
                                              kIOMatchedNotification,
                                              matchingDict,
                                              deviceAdded,
                                              observer,
                                              &portIterator)
        deviceAdded(nil, iterator: portIterator)


        // MARK: - USB remove Notification
        kr = IOServiceAddMatchingNotification(gNotifyPort,
                                              kIOTerminatedNotification,
                                              matchingDict,
                                              deviceRemoved,
                                              observer,
                                              &portIterator)
        deviceRemoved(nil, iterator: portIterator)

    }
}

func deviceAdded(refCon: UnsafeMutablePointer, iterator: io_iterator_t) -> Void {
    var kr: kern_return_t = KERN_FAILURE

    while case let usbDevice = IOIteratorNext(iterator) where usbDevice != 0 {
        let deviceNameAsCFString = UnsafeMutablePointer.alloc(1)
        defer {deviceNameAsCFString.dealloc(1)}
        kr = IORegistryEntryGetName(usbDevice, UnsafeMutablePointer(deviceNameAsCFString))
        if kr != KERN_SUCCESS {
            deviceNameAsCFString.memory.0 = 0
        }
        let deviceName = String.fromCString(UnsafePointer(deviceNameAsCFString))
        print("Device Added: \(deviceName!)")

        // Do something if I get the specific device
        if deviceName == "YOUR DEVICE" {
            /// Your Action HERE
        }

        IOObjectRelease(usbDevice)
    }
}