How to detect if a key is pressed on OS X?

Question

I'm writing a game in Spritekit for OSX. How to check if a key is currently being pressed? Consider this example:

//some code. this could be e.g. inside a game loop

if (/*is key 'w' pressed*/) {
    // move forward
}

//some more code

Both Swift and Objective-C solutions are useful.

Note: I am not interested in receiving or dealing with the event, so I'd like to avoid that if possible. I only need to check whether a specific key is currently pressed or not.

Note #2: This question is not a duplicate of the linked question, as it only addresses the issue from the perspective of receiving the 'keyPressed' event (as a parameter to a method call), not from the perspective of performing a check elsewhere to find out whether a key is currently being pressed. In other words, it does not help me fill in the condition in the if-statement above.

I'm thinking I may have to end up maintaining an Array of booleans, one for each keycode, and updating its contents as I receive keyDown and keyUp events. But I was hoping for a more elegant solution as this seems pretty trivial functionality.

Answer 1

If it's more convenient to poll instead of receiving notifications, you could use the Quartz Event Services function CGEventSourceKeyState.