A block-based CADisplayLink for Swift

DisplayLink.swift

import QuartzCore

/// A block-based CADisplayLink wrapper.
/// You are expected to retain this until you no longer need it.
/// To prevent a retain cycle, you must use [unowned self] in the callback you pass.
public class DisplayLink {

  public init (_ callback: Void -> Void) {
    _callback = callback
    _link = CADisplayLink(target: _DisplayTarget(self), selector: "_callback")
    _link.addToRunLoop(NSRunLoop.mainRunLoop(), forMode: NSRunLoopCommonModes)
  }

  private let _callback: Void -> Void

  private let _link: CADisplayLink!

  deinit {
    _link.invalidate()
  }
}

/// Retained by CADisplayLink.
private class _DisplayTarget {

  init (_ link: DisplayLink) {
    _link = link
  }

  weak var _link: DisplayLink!

  @objc func _callback () {
    _link?._callback()
  }
}

Swift 5

public class DisplayLink {
    
    public init (_ callback: @escaping () -> Void) {
        _callback = callback
        _link = CADisplayLink(target: _DisplayTarget(self), selector: #selector(_DisplayTarget._callback))
        _link.add(to: RunLoop.main, forMode: RunLoop.Mode.common)
    }
    
    fileprivate let _callback: () -> Void
    
    private var _link: CADisplayLink!
    
    deinit {
        _link.invalidate()
    }

    func pause() {
        _link.isPaused = true
    }
    func resume() {
        _link.isPaused = false
    }
}

/// Retained by CADisplayLink.
fileprivate class _DisplayTarget {
    
    init (_ link: DisplayLink) {
        _link = link
    }
    
    weak var _link: DisplayLink!
    
    @objc func _callback () {
        _link?._callback()
    }
}