Scheduling IOHIDManager with runloop in a GUI App - swift

Question

I am writing an app that is monitoring input from a gamepad in swift.
I managed to build a command-line application with the intended behavior :
import Foundation
import IOKit.hid
var valueCallback : IOHIDValueCallback = {
(context, result, sender, value) in
let element = IOHIDValueGetElement(value)
print(IOHIDElementGetUsage(element), IOHIDValueGetIntegerValue(value))
}
var attachCallback : IOHIDDeviceCallback = {
(context, result, sender, device) in
IOHIDDeviceOpen(device, IOOptionBits(kIOHIDOptionsTypeSeizeDevice))
IOHIDDeviceRegisterInputValueCallback(device, valueCallback, context)
print("Controller attached")
}
var detachCallback : IOHIDDeviceCallback = {
(context, result, sender, device) in
print("Controller detached")
}
class HID {
let manager = IOHIDManagerCreate(kCFAllocatorDefault, IOOptionBits(kIOHIDOptionsTypeNone))
let devices = [kIOHIDTransportKey: "Bluetooth"] as CFDictionary
init() {
IOHIDManagerSetDeviceMatching(self.manager, self.devices)
IOHIDManagerRegisterDeviceMatchingCallback(self.manager, attachCallback, nil)
IOHIDManagerRegisterDeviceRemovalCallback(self.manager, detachCallback, nil)
IOHIDManagerScheduleWithRunLoop(self.manager, CFRunLoopGetCurrent(), CFRunLoopMode.defaultMode.rawValue)
IOHIDManagerOpen(self.manager, IOOptionBits(kIOHIDOptionsTypeNone))
}
}
var hidTest = HID()
CFRunLoopRun()
I then want to use this inside an actual app, but it then doesn't work as intended. I used the same code for the class and callbacks, and tried this in the AppDelegate :
import Cocoa
import SwiftUI
import AppKit
import IOKit.hid
import Foundation
#main
class AppDelegate: NSObject, NSApplicationDelegate {
var window: NSWindow!
func applicationDidFinishLaunching(_ aNotification: Notification) {
let contentView = ContentView()
window = NSWindow(
contentRect: NSRect(x: 0, y: 0, width: 480, height: 300),
styleMask: [.titled, .closable, .miniaturizable, .resizable, .fullSizeContentView],
backing: .buffered, defer: false)
window.isReleasedWhenClosed = false
window.center()
window.setFrameAutosaveName("Main Window")
window.contentView = NSHostingView(rootView: contentView)
window.makeKeyAndOrderFront(nil)
let hidTest = HID()
CFRunLoopRun()
}
}
Everything compiles fine, but I am not able to get any value from the gamepad. I think the problem is there : IOHIDManagerScheduleWithRunLoop(self.manager, CFRunLoopGetCurrent(), CFRunLoopMode.defaultMode.rawValue) because the manager is probably not attached to the app's RunLoop.
Is there something specific I need to do to make this work ?
Thanks in advance !

Answer 1

I'm not a Swift expert, but I do know about IOKit and runloops, so I'll attempt an answer.
I think it's likely there is a problem with the call to CFRunLoopRun(). Cocoa apps already run in a runloop which is implicitly created and run by NSApplication. Don't explicitly run the runloop, just allow applicationDidFinishLaunching to return.
When you do this, you should probably make your HID object a member of your application object or similar, or it'll be destroyed. I'm not sure if the Swift bindings for IOKit perform any automatic resource destruction; if so, this would presumably destroy the HID manager object, which you probably want to stay alive for the duration of you application's lifetime.