[英]Correct handling / cleanup / etc of CADisplayLink in Swift custom animation?
使用CADisplayLink
考慮這個簡單的同步動畫,
var link:CADisplayLink?
var startTime:Double = 0.0
let animTime:Double = 0.2
let animMaxVal:CGFloat = 0.4
private func yourAnim()
{
if ( link != nil )
{
link!.paused = true
//A:
link!.removeFromRunLoop(
NSRunLoop.mainRunLoop(), forMode:NSDefaultRunLoopMode)
link = nil
}
link = CADisplayLink(target: self, selector: #selector(doorStep) )
startTime = CACurrentMediaTime()
link!.addToRunLoop(
NSRunLoop.currentRunLoop(), forMode:NSDefaultRunLoopMode)
}
func doorStep()
{
let elapsed = CACurrentMediaTime() - startTime
var ping = elapsed
if (elapsed > (animTime / 2.0)) {ping = animTime - elapsed}
let frac = ping / (animTime / 2.0)
yourAnimFunction(CGFloat(frac) * animMaxVal)
if (elapsed > animTime)
{
//B:
link!.paused = true
link!.removeFromRunLoop(
NSRunLoop.mainRunLoop(), forMode:NSDefaultRunLoopMode)
link = nil
yourAnimFunction(0.0)
}
}
func killAnimation()
{
// for example if the cell disappears or is reused
//C:
????!!!!
}
似乎存在各種問題。
在(A :),即使link
不為null,也可能無法從運行循環中刪除它。 (例如,某人可能已使用link = link:CADisplayLink()
對其進行初始化 - 嘗試進行崩潰。)
其次在(B :)它似乎是一團糟...肯定有一個更好的(和更多的Swift)方式,如果它是零,即使時間剛剛過期怎么辦?
最后在(C :)如果你想打破這個目標...我感到沮喪並且不知道什么是最好的。
實際上A:和B:的代碼應該是相同的呼叫權限,是一種清理呼叫。
這是一個簡單的例子,展示了我如何實現CADisplayLink
(在Swift 3中):
class C { // your view class or whatever
private var displayLink: CADisplayLink?
private var startTime = 0.0
private let animLength = 5.0
func startDisplayLink() {
stopDisplayLink() // make sure to stop a previous running display link
startTime = CACurrentMediaTime() // reset start time
// create displayLink & add it to the run-loop
let displayLink = CADisplayLink(
target: self, selector: #selector(displayLinkDidFire)
)
displayLink.add(to: .main, forMode: .commonModes)
self.displayLink = displayLink
}
@objc func displayLinkDidFire(_ displayLink: CADisplayLink) {
var elapsed = CACurrentMediaTime() - startTime
if elapsed > animLength {
stopDisplayLink()
elapsed = animLength // clamp the elapsed time to the anim length
}
// do your animation logic here
}
// invalidate display link if it's non-nil, then set to nil
func stopDisplayLink() {
displayLink?.invalidate()
displayLink = nil
}
}
注意事項:
nil
來表示顯示鏈接未運行的狀態 - 因為沒有簡單的方法從無效的顯示鏈接獲取此信息。 invalidate()
,而不是使用removeFromRunLoop()
,如果顯示鏈接尚未添加到運行循環中,則不會崩潰。 但是,這種情況絕不應該首先出現 - 因為我們總是在創建后立即將顯示鏈接添加到運行循環中。 displayLink
私有,以防止外部類將其置於意外狀態(例如使其無效但不將其設置為nil
)。 stopDisplayLink()
方法,它既使顯示鏈接無效(如果它是非零)並將其設置為nil
- 而不是復制和粘貼此邏輯。 paused
設置為true
,因為這是多余的。 displayLink
之后,我們使用可選鏈接,例如displayLink?.invalidate()
(如果顯示鏈接不是nil則調用invalidate()
,而不是強制解displayLink
。 雖然力量展開在你給定的情況下可能是“安全的”(因為你正在檢查零) - 在未來的重構時它可能是不安全的,因為你可能會重新構造你的邏輯而不考慮它對力量展開的影響。 elapsed
時間鉗制到動畫持續時間,以確保后面的動畫邏輯不會產生超出預期范圍的值。 displayLinkDidFire(_:)
根據文檔的要求采用 CADisplayLink
類型的單個參數。 我意識到這個問題已經有了一個很好的答案,但這是另一種略有不同的方法,它有助於實現與顯示鏈接幀速率無關的平滑動畫。
**(鏈接到本答案底部的演示項目 - 更新:演示項目源代碼現已更新為Swift 4)
對於我的實現,我選擇將顯示鏈接包裝在它自己的類中,並設置一個委托引用,它將使用增量時間(最后一次顯示鏈接調用和當前調用之間的時間)調用,這樣我們就可以再執行一次動畫了順利。
我目前正在使用這種方法在游戲中同時圍繞屏幕制作約60個視圖。
首先,我們將定義我們的包裝器將調用以通知更新事件的委托協議。
// defines an interface for receiving display update notifications
protocol DisplayUpdateReceiver: class {
func displayWillUpdate(deltaTime: CFTimeInterval)
}
接下來我們將定義我們的顯示鏈接包裝類。 該類將在初始化時采用委托引用。 初始化時,它將自動啟動我們的顯示鏈接,並在deinit上清理它。
import UIKit
class DisplayUpdateNotifier {
// **********************************************
// MARK: Variables
// **********************************************
/// A weak reference to the delegate/listener that will be notified/called on display updates
weak var listener: DisplayUpdateReceiver?
/// The display link that will be initiating our updates
internal var displayLink: CADisplayLink? = nil
/// Tracks the timestamp from the previous displayLink call
internal var lastTime: CFTimeInterval = 0.0
// **********************************************
// MARK: Setup & Tear Down
// **********************************************
deinit {
stopDisplayLink()
}
init(listener: DisplayUpdateReceiver) {
// setup our delegate listener reference
self.listener = listener
// setup & kick off the display link
startDisplayLink()
}
// **********************************************
// MARK: CADisplay Link
// **********************************************
/// Creates a new display link if one is not already running
private func startDisplayLink() {
guard displayLink == nil else {
return
}
displayLink = CADisplayLink(target: self, selector: #selector(linkUpdate))
displayLink?.add(to: .main, forMode: .commonModes)
lastTime = 0.0
}
/// Invalidates and destroys the current display link. Resets timestamp var to zero
private func stopDisplayLink() {
displayLink?.invalidate()
displayLink = nil
lastTime = 0.0
}
/// Notifier function called by display link. Calculates the delta time and passes it in the delegate call.
@objc private func linkUpdate() {
// bail if our display link is no longer valid
guard let displayLink = displayLink else {
return
}
// get the current time
let currentTime = displayLink.timestamp
// calculate delta (
let delta: CFTimeInterval = currentTime - lastTime
// store as previous
lastTime = currentTime
// call delegate
listener?.displayWillUpdate(deltaTime: delta)
}
}
要使用它,只需初始化包裝器的實例,傳入委托偵聽器引用,然后根據增量時間更新動畫。 在此示例中,委托將更新調用傳遞給可動畫視圖(這樣,您可以跟蹤多個動畫視圖,並通過此調用更新每個位置)。
class ViewController: UIViewController, DisplayUpdateReceiver {
var displayLinker: DisplayUpdateNotifier?
var animView: MoveableView?
override func viewDidLoad() {
super.viewDidLoad()
// setup our animatable view and add as subview
animView = MoveableView.init(frame: CGRect.init(x: 150.0, y: 400.0, width: 20.0, height: 20.0))
animView?.configureMovement()
animView?.backgroundColor = .blue
view.addSubview(animView!)
// setup our display link notifier wrapper class
displayLinker = DisplayUpdateNotifier.init(listener: self)
}
// implement DisplayUpdateReceiver function to receive updates from display link wrapper class
func displayWillUpdate(deltaTime: CFTimeInterval) {
// pass the update call off to our animating view or views
_ = animView?.update(deltaTime: deltaTime)
// in this example, the animatable view will remove itself from its superview when its animation is complete and set a flag
// that it's ready to be used. We simply check if it's ready to be recycled, if so we reset its position and add it to
// our view again
if animView?.isReadyForReuse == true {
animView?.reset(center: CGPoint.init(x: CGFloat.random(low: 20.0, high: 300.0), y: CGFloat.random(low: 20.0, high: 700.0)))
view.addSubview(animView!)
}
}
}
我們的可移動視圖更新功能如下所示:
func update(deltaTime: CFTimeInterval) -> Bool {
guard canAnimate == true, isReadyForReuse == false else {
return false
}
// by multiplying our x/y values by the delta time new values are generated that will generate a smooth animation independent of the framerate.
let smoothVel = CGPoint(x: CGFloat(Double(velocity.x)*deltaTime), y: CGFloat(Double(velocity.y)*deltaTime))
let smoothAccel = CGPoint(x: CGFloat(Double(acceleration.x)*deltaTime), y: CGFloat(Double(acceleration.y)*deltaTime))
// update velocity with smoothed acceleration
velocity.adding(point: smoothAccel)
// update center with smoothed velocity
center.adding(point: smoothVel)
currentTime += 0.01
if currentTime >= timeLimit {
canAnimate = false
endAnimation()
return false
}
return true
}
如果您想查看完整的演示項目,可以從GitHub下載: CADisplayLink演示項目
以上是如何有效使用CADisplayLink的最佳示例。 感謝@Fattie和@digitalHound
我無法抗拒使用WKWebView在PdfViewer中使用'digitalHound'添加我對CADisplayLink和DisplayUpdater類的使用。 我的要求是繼續以用戶可選擇的速度自動滾動pdf。
可能這里答案不正確的地方,但我打算在這里展示CADisplayLink的用法。 (對於像我這樣的人,他們可以實現他們的要求。)
//
// PdfViewController.swift
//
import UIKit
import WebKit
class PdfViewController: UIViewController, DisplayUpdateReceiver {
@IBOutlet var mySpeedScrollSlider: UISlider! // UISlider in storyboard
var displayLinker: DisplayUpdateNotifier?
var myPdfFileName = ""
var myPdfFolderPath = ""
var myViewTitle = "Pdf View"
var myCanAnimate = false
var mySlowSkip = 0.0
// 0.125<=slow, 0.25=normal, 0.5=fast, 0.75>=faster
var cuScrollSpeed = 0.25
fileprivate var myPdfWKWebView = WKWebView(frame: CGRect.zero)
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
self.title = myViewTitle
let leftItem = UIBarButtonItem(title: "Back", style: .plain, target: self, action: #selector(PdfViewController.PdfBackClick))
navigationItem.leftBarButtonItem = leftItem
self.view.backgroundColor = UIColor.white.cgColor
mySpeedScrollSlider.minimumValue = 0.05
mySpeedScrollSlider.maximumValue = 4.0
mySpeedScrollSlider.isContinuous = true
mySpeedScrollSlider.addTarget(self, action: #selector(PdfViewController.updateSlider), for: [.valueChanged])
mySpeedScrollSlider.setValue(Float(cuScrollSpeed), animated: false)
mySpeedScrollSlider.backgroundColor = UIColor.white.cgColor
self.configureWebView()
let folderUrl = URL(fileURLWithPath: myPdfFolderPath)
let url = URL(fileURLWithPath: myPdfFolderPath + myPdfFileName)
myPdfWKWebView.loadFileURL(url, allowingReadAccessTo: folderUrl)
}
//MARK: - Button Action
@objc func PdfBackClick()
{
_ = self.navigationController?.popViewController(animated: true)
}
@objc func updateSlider()
{
if ( mySpeedScrollSlider.value <= mySpeedScrollSlider.minimumValue ) {
myCanAnimate = false
} else {
myCanAnimate = true
}
cuScrollSpeed = Double(mySpeedScrollSlider.value)
}
fileprivate func configureWebView() {
myPdfWKWebView.frame = view.bounds
myPdfWKWebView.translatesAutoresizingMaskIntoConstraints = false
myPdfWKWebView.navigationDelegate = self
myPdfWKWebView.isMultipleTouchEnabled = true
myPdfWKWebView.scrollView.alwaysBounceVertical = true
myPdfWKWebView.layer.backgroundColor = UIColor.red.cgColor //test
view.addSubview(myPdfWKWebView)
myPdfWKWebView.topAnchor.constraint(equalTo: topLayoutGuide.bottomAnchor ).isActive = true
myPdfWKWebView.rightAnchor.constraint(equalTo: view.rightAnchor).isActive = true
myPdfWKWebView.leftAnchor.constraint(equalTo: view.leftAnchor).isActive = true
myPdfWKWebView.bottomAnchor.constraint(equalTo: mySpeedScrollSlider.topAnchor).isActive = true
}
//MARK: - DisplayUpdateReceiver delegate
func displayWillUpdate(deltaTime: CFTimeInterval) {
guard myCanAnimate == true else {
return
}
var maxSpeed = 0.0
if cuScrollSpeed < 0.5 {
if mySlowSkip > 0.25 {
mySlowSkip = 0.0
} else {
mySlowSkip += cuScrollSpeed
return
}
maxSpeed = 0.5
} else {
maxSpeed = cuScrollSpeed
}
let scrollViewHeight = self.myPdfWKWebView.scrollView.frame.size.height
let scrollContentSizeHeight = self.myPdfWKWebView.scrollView.contentSize.height
let scrollOffset = self.myPdfWKWebView.scrollView.contentOffset.y
let xOffset = self.myPdfWKWebView.scrollView.contentOffset.x
if (scrollOffset + scrollViewHeight >= scrollContentSizeHeight)
{
return
}
let newYOffset = CGFloat( max( min( deltaTime , 1 ), maxSpeed ) )
self.myPdfWKWebView.scrollView.setContentOffset(CGPoint(x: xOffset, y: scrollOffset+newYOffset), animated: false)
}
}
extension PdfViewController: WKNavigationDelegate {
// MARK: - WKNavigationDelegate
public func webView(_ webView: WKWebView, didStartProvisionalNavigation navigation: WKNavigation!) {
//print("didStartProvisionalNavigation")
}
public func webView(_ webView: WKWebView, didFinish navigation: WKNavigation!) {
//print("didFinish")
displayLinker = DisplayUpdateNotifier.init(listener: self)
myCanAnimate = true
}
public func webView(_ webView: WKWebView, didFailProvisionalNavigation navigation: WKNavigation!, withError error: Error) {
//print("didFailProvisionalNavigation error:\(error)")
}
public func webView(_ webView: WKWebView, didFail navigation: WKNavigation!, withError error: Error) {
//print("didFail")
}
}
示例從另一個視圖調用如下。
從Document文件夾加載PDF文件。
func callPdfViewController( theFileName:String, theFileParentPath:String){
if ( !theFileName.isEmpty && !theFileParentPath.isEmpty ) {
let pdfViewController = self.storyboard!.instantiateViewController(withIdentifier: "PdfViewController") as? PdfViewController
pdfViewController?.myPdfFileName = theFileName
pdfViewController?.myPdfFolderPath = theFileParentPath
self.navigationController!.pushViewController(pdfViewController!, animated: true)
} else {
// Show error.
}
}
可以“修改”此示例以加載網頁並以用戶選擇的速度自動滾動它們。
問候
桑傑。
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