Timer vs CADisplayLink

Timer schedules a callback on a run loop at an interval you choose, once or repeating. Firing is approximate, because a busy run loop delays ticks, and it has no relationship to the display's refresh. Use it for periodic work that doesn't need to run once per frame: polling, debouncing input, and housekeeping that runs every few seconds.

CADisplayLink is driven by the display, firing in sync with screen updates, typically once per frame at the current refresh rate (60 Hz, or up to 120 Hz on ProMotion). Each tick gives you timestamp, targetTimestamp, and duration for frame timing. Use it when output must track the screen: custom per-frame drawing, smooth progress, or sampling a value every frame.

Pick Timer when the schedule is wall-clock or coarse and not tied to drawing. Pick CADisplayLink when work should line up with frames. For most animations, prefer UIViewPropertyAnimator, Core Animation, or SwiftUI's animation system over driving transforms by hand from either one.

Both retain their target when you create them with a target and selector, so prefer the block-based Timer with [weak self]. Invalidate either one when the work is done, such as in viewDidDisappear. Don't wait for deinit, because a timer that retains its target keeps deinit from ever running, so you leak the owner and burn CPU.

let timer = Timer(timeInterval: 0.25, repeats: true) { [weak self] _ in
    self?.tick()
}
RunLoop.main.add(timer, forMode: .common)

private var lastFrameTimestamp: CFTimeInterval?

displayLink = CADisplayLink(target: self, selector: #selector(step(_:)))
displayLink?.add(to: .main, forMode: .common)

@objc func step(_ link: CADisplayLink) {
    let previous = lastFrameTimestamp ?? link.timestamp
    let dt = link.timestamp - previous
    lastFrameTimestamp = link.timestamp
    advanceAnimation(by: dt)
}