How to set CADisplayLink in Swift with weak reference between target and CADisplayLink instance

Question

In Objective-C, we can init CADisplayLink with Proxy Pattern to break strong reference:

WeakProxy *weakProxy = [WeakProxy weakProxyForObject:self];
self.displayL         


        

Answer 1

Another solution, this one hides the proxy / objc runtime from its external API. The DisplayLink stays alive for as long as it is referenced by variable. Once the variable goes out of scope or is set to nil, the CADisplayLink is invalidated so that the target can be deinited also.

import Foundation
import UIKit

/// DisplayLink provides a block based interface for CADisplayLink.
/// The CADisplayLink is invalidated upon DisplayLink deinit.
///
/// Usage:
/// ```
/// let displayLink = DisplayLink { caDisplayLink in print("Next frame scheduled \(caDisplayLink.targetTimestamp)") }
/// ```
///
/// Note: Keep a reference to the DisplayLink.
final class DisplayLink {
    let displayLink: CADisplayLink

    init(runloop: RunLoop? = .main, prepareNextFrame: @escaping (CADisplayLink) -> ()) {
        displayLink = CADisplayLink(
            target: DisplayLinkTarget(prepareNextFrame),
            selector: #selector(DisplayLinkTarget.prepareNextFrame))

        if let runloop = runloop {
            displayLink.add(to: runloop, forMode: .default)
        }
    }

    deinit {
        displayLink.invalidate()
    }
}

private class DisplayLinkTarget {
    let callback: (CADisplayLink) -> ()

    init(_ callback: @escaping (CADisplayLink) -> ()) {
        self.callback = callback
    }

    @objc func prepareNextFrame(displaylink: CADisplayLink) {
        callback(displaylink)
    }
}