快速计时器滞后

Question

我知道Timer 不能保证完全按照您要求的速度运行。 但是，我刚刚开始了一个全新的项目：

class ViewController: NSViewController {

    var timer = Timer()
    var count: Double = 0.0
    var timeStamp: Date = Date()

override func viewDidLoad() {
    super.viewDidLoad()
    self.timer = Timer.scheduledTimer(timeInterval: 0.1,
                                      target: self,
                                      selector: #selector(self.updateCounting),
                                      userInfo: nil,
                                      repeats: true)
}

@objc func updateCounting(){
    let duration = self.timeStamp.distance(to: Date())
    print("Counting \(self.count) vs. Real life \(duration)")
    self.count = self.count + 0.1
}

}

我希望在 count 和 duration 之间得到大致相同的结果，但我看到了这样奇怪的事情：

Counting 60.50000000000059 vs. Real life 60.64057409763336
Counting 60.60000000000059 vs. Real life 60.741435050964355
Counting 60.70000000000059 vs. Real life 70.84065008163452
Counting 60.800000000000594 vs. Real life 80.94094407558441
Counting 60.900000000000595 vs. Real life 82.99448704719543

在 Xcode 11.5、iMac 和 MacBook Pro 上测试。 我在这里做错了吗？

Answer 1

没错，但您错过了Mac 应用程序的能源效率指南：

• Prioritize Work at the App Level
• Prioritize Work at the Task Level
• Best Practices

你的应用只是在打盹。

检查ProcessInfo 并搜索管理活动。一个例子（不好的）是将您的AppDelegate.swift 更改为：

@NSApplicationMain
class AppDelegate: NSObject, NSApplicationDelegate {
    private var activity: NSObjectProtocol!

    func applicationDidFinishLaunching(_ aNotification: Notification) {
        let options: ProcessInfo.ActivityOptions = [.userInitiatedAllowingIdleSystemSleep]
        let reason = "No napping!"
        self.activity = ProcessInfo.processInfo.beginActivity(options: options, reason: reason)
    }

    func applicationWillTerminate(_ aNotification: Notification) {
        ProcessInfo.processInfo.endActivity(activity)
    }
}

但不要这样做，这对用户、MacBook Pro 电池寿命等都是不利的。