[英]How to set CADisplayLink in Swift with weak reference between target and CADisplayLink instance
在 Objective-C 中,我們可以使用代理模式初始化 CADisplayLink 來打破強引用:
WeakProxy *weakProxy = [WeakProxy weakProxyForObject:self];
self.displayLink = [CADisplayLink displayLinkWithTarget:weakProxy selector:@selector(displayDidRefresh:)];
然后,只需使dealloc
的 displayLink 無效:
- (void)dealloc
{
[_displayLink invalidate];
}
但是,NSProxy 似乎無法在 Swift 中繼承: https : //bugs.swift.org/browse/SR-1715
我試着這樣寫:
weak var weakSelf = self
displayLink = CADisplayLink(target: weakSelf!, selector: #selector(displayDidRefresh(dpLink:)))
它沒有用。
我想知道是否有任何方法可以像在 Objective-C 中那樣實現這一目標。
更好的方法可能是使viewWill/DidDisappear
的顯示鏈接無效,另見
有用的信息。
如果這不是一個選項:使代理對象繼承自NSObject
而不是NSProxy
。 例如,這里給出了一個 Objective-C 解決方案
並且可以輕松轉換為 Swift 3:
class JAWeakProxy: NSObject {
weak var target: NSObjectProtocol?
init(target: NSObjectProtocol) {
self.target = target
super.init()
}
override func responds(to aSelector: Selector!) -> Bool {
return (target?.responds(to: aSelector) ?? false) || super.responds(to: aSelector)
}
override func forwardingTarget(for aSelector: Selector!) -> Any? {
return target
}
}
然后可以用作
displayLink = CADisplayLink(target: JAWeakProxy(target: self),
selector: #selector(didRefresh(dpLink:)))
你的方法
weak var weakSelf = self
displayLink = CADisplayLink(target: weakSelf!, selector: #selector(displayDidRefresh(dpLink:)))
不工作,因為它解開weakSelf
當CADisplayLink
被初始化並傳遞一個強有力的參考self
為目標。
這個代理類應該可以正常工作。 不要忘記在 dealloc 之前失效。
import UIKit
class CADisplayLinkProxy {
var displaylink: CADisplayLink?
var handle: (() -> Void)?
init(handle: (() -> Void)?) {
self.handle = handle
displaylink = CADisplayLink(target: self, selector: #selector(updateHandle))
displaylink?.add(to: RunLoop.current, forMode: .common)
}
@objc func updateHandle() {
handle?()
}
func invalidate() {
displaylink?.remove(from: RunLoop.current, forMode: .common)
displaylink?.invalidate()
displaylink = nil
}
}
用法:
class ViewController: UIViewController {
var displaylinkProxy: CADisplayLinkProxy?
override func viewDidLoad() {
super.viewDidLoad()
displaylinkProxy = CADisplayLinkProxy(handle: { [weak self] in
self?.updateAnything()
})
}
@objc func updateAnything() {
print(Date())
}
}
另一種解決方案,這個解決方案對它的外部 API 隱藏了代理/objc 運行時。 只要它被變量引用, DisplayLink
保持活動狀態。 一旦變量超出范圍或設置為 nil,CADisplayLink 將失效,以便也可以取消目標。
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)
}
}
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