你如何在Swift中使用CGEventTapCreate？

typealias CGEventTapCallBACk = CFunctionPointer<((CGEventTapProxy,CGEventType,CGEvent!,UnsafeMutablePointer<Void>) -> Unmanaged<CGEvent>!)>

let eventTapCallBACkBlock : @objc_block
(CGEventTapProxy,CGEventRef,UnsafeMutablePointer<Void>) -> CGEventRef =
{ (eventTapProxy: CGEventTapProxy,eventType: CGEventType,event: CGEventRef,refcon: UnsafeMutablePointer<Void>) in
  return event
}

CGEventTapCreate()的回调参数是一个C函数指针,
在Swift 1.x中,不可能使用Swift函数参数调用它.

但是,在Swift 2(Xcode 7)中,C函数接受函数指针参数
可以使用闭包或全局函数调用(具有限制
闭包不得捕获任何本地语境).

作为一个例子,这里是一个完整的翻译
Receiving,Filtering,and Modifying Key Presses and Releases
到斯威夫特：

import Foundation

func myCGEventCallBACk(proxy : CGEventTapProxy,type : CGEventType,event : CGEvent,refcon : UnsafeMutablePointer<Void>) -> Unmanaged<CGEvent>? {

    if [.KeyDown,.KeyUp].contains(typE) {
        var keyCode = CGEventGetIntegerValueField(event,.KeyboardEventKeycodE)
        if keyCode == 0 {
            keyCode = 6
        } else if keyCode == 6 {
            keyCode = 0
        }
        CGEventSetIntegerValueField(event,.KeyboardEventKeycode,keyCodE)
    }
    return Unmanaged.passRetained(event)
}

let eventMask = (1 << CGEventType.KeyDown.rawvalue) | (1 << CGEventType.KeyUp.rawvalue)
guard let eventTap = CGEventTapCreate(.CGSessionEventTap,.HeadInsertEventTap,.Default,CGEventMask(eventMask),myCGEventCallBACk,nil) else {
        print("Failed to create event tap")
        exit(1)
}

let runLoopsource = CFMachPortCreateRunLoopsource(kcfAllocatorDefault,eventTap,0)
CFRunLoopAddsource(CFRunLoopGetCurrent(),runLoopsource,kcfRunLoopCommonModes)
CGEventTapEnable(eventTap,truE)
CFRunLoopRun()

Swift 3更新：

import Foundation

func myCGEventCallBACk(proxy: CGEventTapProxy,type: CGEventType,event: CGEvent,refcon: UnsafeMutableRawPointer?) -> Unmanaged<CGEvent>? {

    if [.keyDown,.keyUp].contains(typE) {
        var keyCode = event.getIntegerValueField(.keyboardEventKeycodE)
        if keyCode == 0 {
            keyCode = 6
        } else if keyCode == 6 {
            keyCode = 0
        }
        event.setIntegerValueField(.keyboardEventKeycode,value: keyCodE)
    }
    return Unmanaged.passRetained(event)
}

let eventMask = (1 << CGEventType.keyDown.rawvalue) | (1 << CGEventType.keyUp.rawvalue)
guard let eventTap = CGEvent.tapCreate(tap: .cgSessionEventTap,place: .headInsertEventTap,options: .defaultTap,eventsOfInterest: CGEventMask(eventMask),callBACk: myCGEventCallBACk,userInfo: nil) else {
                                        print("Failed to create event tap")
                                        exit(1)
}

let runLoopsource = CFMachPortCreateRunLoopsource(kcfAllocatorDefault,.commonModes)
CGEvent.tapEnable(tap: eventTap,enable: truE)
CFRunLoopRun()