Simulate keypress using Swift

Question

I'm searching for a way to simulate keystrokes in OSX. I found another solution (Simulate keypress for system wide hotkeys) using Objective-C, but i need to do it with Swift. How can i adapt CGEventCreateKeyboardEvent?

Solution 1

The code on that linked answer is fairly readily convertible to Swift code, however there are a handful of gotchas you will need to take care of along the way:

CGEventSourceCreate takes a CGEventSourceStateID, which is a typealiase for a UInt32, but the constants such as kCGEventSourceStateHIDSystemState are defined as Int, so you’ll have to cast them i.e. CGEventSourceStateID(kCGEventSourceStateHIDSystemState). Likewise with CGEventFlags.

CGEventSourceCreate and CGEventCreateKeyboardEvent return an Unmanaged<CGEventSource> (or Unmanaged<CGEvent>). The auto-generated Swift API for Core Graphics doesn’t know whether the returned objects need to be released by you or not so you need to check the API docs for these calls and then use takeRetainedValue() or takeUnretainedValue() accordingly on the returned value, to convert them into the underlying type you want to work with.

Finally, they return implicitly unwrapped optionals, so you’ll need to decide if you want to check for nils or just live with the excitement of runtime explosions if they ever return one.

Given all that it’s pretty simple to turn the Objective-C in that answer demonstrating pressing Cmd-Space to Swift, I just tried pasting this into a scratch app and it worked fine:

(though I haven't checked the API docs for whether the retain is the correct thing to do or not)

let src = CGEventSourceCreate(CGEventSourceStateID(kCGEventSourceStateHIDSystemState)).takeRetainedValue()

let cmdd = CGEventCreateKeyboardEvent(src, 0x38, true).takeRetainedValue()
let cmdu = CGEventCreateKeyboardEvent(src, 0x38, false).takeRetainedValue()
let spcd = CGEventCreateKeyboardEvent(src, 0x31, true).takeRetainedValue()
let spcu = CGEventCreateKeyboardEvent(src, 0x31, false).takeRetainedValue()

CGEventSetFlags(spcd, CGEventFlags(kCGEventFlagMaskCommand));
CGEventSetFlags(spcd, CGEventFlags(kCGEventFlagMaskCommand));

let loc = CGEventTapLocation(kCGHIDEventTap)

CGEventPost(loc, cmdd)
CGEventPost(loc, spcd)
CGEventPost(loc, spcu)
CGEventPost(loc, cmdu)

Solution 2

Working with Swift 3

let src = CGEventSource(stateID: CGEventSourceStateID.hidSystemState)

let cmdd = CGEvent(keyboardEventSource: src, virtualKey: 0x38, keyDown: true)
let cmdu = CGEvent(keyboardEventSource: src, virtualKey: 0x38, keyDown: false)
let spcd = CGEvent(keyboardEventSource: src, virtualKey: 0x31, keyDown: true)
let spcu = CGEvent(keyboardEventSource: src, virtualKey: 0x31, keyDown: false)

spcd?.flags = CGEventFlags.maskCommand;

let loc = CGEventTapLocation.cghidEventTap

cmdd?.post(tap: loc)
spcd?.post(tap: loc)
spcu?.post(tap: loc)
cmdu?.post(tap: loc)

Solution 3

Swift 3

For me the hexadecimal key values like: 0x124 didn't work, but simple UInt 124 did the trick!

A nice collection of keycodes can be found here! This copy-paste code snippet simulates a right arrow keypress. Change the key number for whatever you want to simulate:

    // Simulate Right Arrow keypress
    let rightArrowKeyCode: UInt16 = 124

    let keyDownEvent = CGEvent(keyboardEventSource: nil, virtualKey: rightArrowKeyCode, keyDown: true)
    keyDownEvent?.flags = CGEventFlags.maskCommand
    keyDownEvent?.post(tap: CGEventTapLocation.cghidEventTap)

    let keyUpEvent = CGEvent(keyboardEventSource: nil, virtualKey: rightArrowKeyCode, keyDown: false)
    keyUpEvent?.flags = CGEventFlags.maskCommand
    keyUpEvent?.post(tap: CGEventTapLocation.cghidEventTap)

Update: For macOS Mojave and above you should allow your app to control your computer in System Preferences > Security & Privacy > Accessibility

Solution 4

I made this for a Swift 4 project, don't forget that App sandboxing will not allow an app to send keystrokes like this so it'll need to be turned off. This means your app would prohibited from the AppStore.

import Foundation

class FakeKey {
    static func send(_ keyCode: CGKeyCode, useCommandFlag: Bool) {
        let sourceRef = CGEventSource(stateID: .combinedSessionState)

        if sourceRef == nil {
            NSLog("FakeKey: No event source")
            return
        }

        let keyDownEvent = CGEvent(keyboardEventSource: sourceRef,
                                   virtualKey: keyCode,
                                   keyDown: true)
        if useCommandFlag {
            keyDownEvent?.flags = .maskCommand
        }

        let keyUpEvent = CGEvent(keyboardEventSource: sourceRef,
                                 virtualKey: keyCode,
                                 keyDown: false)

        keyDownEvent?.post(tap: .cghidEventTap)
        keyUpEvent?.post(tap: .cghidEventTap)
    }
}

View more solutions

Comments

[Kaunteya]

@Airspeed: nice answer. Although can we make the "hex key values" to something more readable like KVK_ANSI_A

[Nisba]

I have transalted, I post it in an answer

[ocodo]

There's a list of key symbols in Carbon.HIToolbox in the format kVK_... for example kVK_ANSI_M is the M key.

[ocodo]

Unfortunately I don't have Mojave installed, please post the fix that you find as a new answer. You may want to file a bug with Apple. (This code is basically using the same APIs as the other answers.)

[mike]

The issue seems related to the "accessibility" API. You need to grant it permission in order to use it. In my case it failed "silently" b/c I denied the permission prompt once.

[ocodo]

That's "good" news, There's no problem, it's just the way Apple designed it.

[Duck]

it is amazing how we have to relate on other developers posting this kind of info. Apple shoud fire satan from running the documentation department and hire some competent people. Their docs stink.

[Jason Denney]

In my case (Swift 5), I had to use: let src = CGEventSource(stateID: .privateState)

[Leo Dabus]

It does work under Mojave but you need to allow your app to control your computer in the system preferences > security & privacy > accessibility

[ocodo]

Hi Sam, this is close enough to my Swift 4 version that it makes sense to just paste them together merging the diff. Happy to do it for you, but I figured I'd give you the opportunity to do the edit first.

[ocodo]

A version I keep updated for cutbox/CutBox gist.github.com/jasonm23/3d2c4040a5f879a945264d1bd0a630ad

[Anoop Vaidya]

hi, if you can help me on this stackoverflow.com/questions/68902254/…

[Dominik Bucher]

This seems like it is not working with macOS Mojave. Can anyone confirm? It waw working perfectly fine before..