简短回答:使用 CADisplayLink 每 n 帧调用一次.示例代码:

Short answer: use CADisplayLink to get called every n frames. Sample code:

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)
    let displayLink = CADisplayLink(target: self, selector: #selector(animationDidUpdate))
    displayLink.preferredFramesPerSecond = 50
    displayLink.add(to: .main, forMode: .defaultRunLoopMode)
    updateValues()
}

var animationComplete = false
var lastUpdateTime = CACurrentMediaTime()
func updateValues() {
    self.emaxView.animate(0);
    lastUpdateTime = CACurrentMediaTime()
    animationComplete = false
}

func animationDidUpdate(displayLink: CADisplayLink) {

    if(!animationComplete) {
        let now = CACurrentMediaTime()
        let interval = (CACurrentMediaTime() - lastUpdateTime)/animationDuration
        self.emaxView.animate(min(CGFloat(interval), 1))
        animationComplete = interval >= 1.0
    }
}

}

代码可以改进和概括，但它正在做我需要的工作.

The code could be refined and generalised but it's doing the job I needed.