How do you use CGEventTapCreate in Swift?

Question

Has anyone managed to get this function to work in Swift?

Here is a reference SO post from last year: Using CGEventTapCreate Trouble with parameters in Swift

Apple Doc: https://developer.apple.com/library/prerelease/mac/documentation/Carbon/Reference/QuartzEventServicesRef/index.html#//apple_ref/c/func/CGEventTapCreate

Here is how the CGEventTapCallBack is defined:

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

Here is how I've written the block:

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

Then I've called CGEventTapCreate with the callback parameter like unsafeBitCast(eventTapCallBackBlock, CGEventTapCallBack.self)

I get a valid CFMachPortRef back, but at run time I get an access violation exception on first event. It would "seem" I'm close to a solution in swift in its current release state.

Using Xcode Version 6.4

Answer 1

The callback parameter of CGEventTapCreate() is a C function pointer, and in Swift 1.x it is not possible call it with a Swift function argument.

However, in Swift 2 (Xcode 7), C functions that take function pointer arguments can be called using closures or global functions (with the restriction that the closure must not capture any of its local context).

As an example, here is a complete translation of Receiving, Filtering, and Modifying Key Presses and Releases to Swift 3.

import Foundation
import CoreGraphics

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.passUnretained(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, eventTap, 0)
CFRunLoopAddSource(CFRunLoopGetCurrent(), runLoopSource, .commonModes)
CGEvent.tapEnable(tap: eventTap, enable: true)
CFRunLoopRun()