How to convert Swift array into CFArray? - objective-c

Question

I'm trying to capture a window list in a Mac OS X app using Swift. The CGWindowListCreateImageFromArray function requires a CFArray. I've tried several things and this is the closest I've got. Or is there a better way to convert the array?
import Cocoa
// Example swift array of CGWindowID's
var windowIDs = [CGWindowID]();
windowIDs.append(1);
windowIDs.append(2);
// Convert to CFArray using CFArrayCreate
let allocator = kCFAllocatorDefault
let numValues = windowIDs.count as CFIndex
let callbacks: UnsafePointer<CFArrayCallBacks> = nil
var values: UnsafeMutablePointer<UnsafePointer<Void>> = nil
/* how do I convert windowIDs to UnsafeMutablePointer<UnsafePointer<Void>> for the values? */
let windowIDsCFArray = CFArrayCreate(allocator, values, numValues, callbacks);
let capture = CGWindowListCreateImageFromArray(CGRectInfinite, windowIDsCFArray, CGWindowImageOption(kCGWindowListOptionOnScreenOnly));

Answer 1

You can initialize your UnsafeMutablePointer with your array so long as you set your CGWindowIDs to CFTypeRef:
var windows: [CFTypeRef] = [1, 2]
var windowsPointer = UnsafeMutablePointer<UnsafePointer<Void>>(windows)
var cfArray = CFArrayCreate(nil, windowsPointer, windows.count, nil)

Answer 2

Converted Ian's answer to Swift 4:
let windows = [CGWindowID(17), CGWindowID(50), CGWindowID(59)]
let pointer = UnsafeMutablePointer<UnsafeRawPointer?>.allocate(capacity: windows.count)
for (index, window) in windows.enumerated() {
pointer[index] = UnsafeRawPointer(bitPattern: UInt(window))
}
let array: CFArray = CFArrayCreate(kCFAllocatorDefault, pointer, windows.count, nil)
let capture = CGImage(windowListFromArrayScreenBounds: CGRect.infinite, windowArray: array, imageOption: [])!
let image: NSImage = NSImage(cgImage: capture, size: NSSize.zero)
Swift.print(image)

Answer 3

Arrays in Swift are bridged to NSArray, given they contain objects, e.g., conform to [AnyObject] type. Since CGWindowID is a UInt32, you need to convert it to NS family, array's map() method is an elegant approach.
var windows: [CGWindowID] = [CGWindowID(1), CGWindowID(2)]
var array: CFArray = windows.map({NSNumber(unsignedInt: $0)}) as CFArray
This, however, doesn't reflect on the actual CGWindowListCreateImageFromArray problem. Here's the working solution for that:
let windows: [CGWindowID] = [CGWindowID(17), CGWindowID(50), CGWindowID(59)]
let pointer: UnsafeMutablePointer<UnsafePointer<Void>> = UnsafeMutablePointer<UnsafePointer<Void>>.alloc(windows.count)
for var i: Int = 0, n = windows.count; i < n; i++ {
pointer[i] = UnsafePointer<Void>(bitPattern: UInt(windows[i]))
}
let array: CFArray = CFArrayCreate(kCFAllocatorDefault, pointer, windows.count, nil)
let capture: CGImage = CGWindowListCreateImageFromArray(CGRectInfinite, array, CGWindowImageOption.Default)!
let image: NSImage = NSImage(CGImage: capture, size: NSZeroSize)
Swift.print(image) // <NSImage 0x7f83a3d16920 Size={1440, 900} Reps=("<NSCGImageSnapshotRep:0x7f83a3d2dea0 cgImage=<CGImage 0x7f83a3d16840>>")>
I'm not great at ObjC, please correct if wrong, but from what I understand by playing with the SonOfGrab example and particular piece of code below is that the final pointer structure contains window ids (UInt32) not inside the memory cell (memory property of UnsafePointer instance), but inside memory address (hashValue property).
const void *windowIDs[2];
windowIDs[0] = 10;
windowIDs[1] = 20;
It's interesting, since values aren't stored in the memory, but inside the address descriptors, with oldest architectures being 32-bit UInt32 values fit perfectly into address pointers. Perhaps back in the days when the memory was a limiting factor this made a lot of sense and was a great approach. Discovering this all night in Swift in 2016 made me suicidal.
What's worse it fails in Xcode 7.2 playground with certain window ids, probably because of the way it handles memory, but works in the actual app.