swift - 发布日期倒计时器

Question

您好，我正在尝试处理此代码，但我的问题出在代码的一部分上:

countdownTimer = Timer.scheduledTimer(timeInterval: 1, target: (Any).self, selector: #selector(updateTime), userInfo: nil, repeats: true)

这是 Xcode 中的错误消息

Argument of '#selector' cannot refer to global function 'updateTime()'

我无法处理这个问题。可能出什么问题了？谢谢你

import UIKit
import Foundation
var releaseDate: NSDate?
var countdownTimer = Timer()

func startTimer() {

    let releaseDateString = "2019-02-23 08:00:00"
    let releaseDateFormatter = DateFormatter()
    releaseDateFormatter.dateFormat = "yyyy-MM-dd HH:mm:ss"
    releaseDate = releaseDateFormatter.date(from: releaseDateString)! as NSDate

    countdownTimer = Timer.scheduledTimer(timeInterval: 1, target: (Any).self, selector: #selector(updateTime), userInfo: nil, repeats: true)
}

func updateTime() {

    let currentDate = Date()
    let calendar = Calendar.current

    let diffDateComponents = calendar.dateComponents([.day, .hour, .minute, .second], from: currentDate, to: releaseDate! as Date)

    let countdown = "Days \(diffDateComponents.day ?? 0), Hours \(diffDateComponents.hour ?? 0), Minutes \(diffDateComponents.minute ?? 0), Seconds \(diffDateComponents.second ?? 0)"

    print(countdown)
}

Answer 1

您不能在#selector中使用全局函数。所以把它移到一个类中。另外，如果您要使用基于选择器的计时器，则 updateTime 必须标记为 @objc。

或者，如果您确实想使用全局函数，只需使用基于 block 的计时器:

var releaseDate: Date?
var countdownTimer = Timer()

func startTimer() {
    let releaseDateString = "2019-02-23 08:00:00"
    let releaseDateFormatter = DateFormatter()
    releaseDateFormatter.dateFormat = "yyyy-MM-dd HH:mm:ss"
    releaseDate = releaseDateFormatter.date(from: releaseDateString)

    countdownTimer = Timer.scheduledTimer(withTimeInterval: 1, repeats: true) { _ in
        updateTime()
    }
}

func updateTime() {
    let currentDate = Date()
    let calendar = Calendar.current

    let diffDateComponents = calendar.dateComponents([.day, .hour, .minute, .second], from: currentDate, to: releaseDate!)

    let countdown = "Days \(diffDateComponents.day ?? 0), Hours \(diffDateComponents.hour ?? 0), Minutes \(diffDateComponents.minute ?? 0), Seconds \(diffDateComponents.second ?? 0)"

    print(countdown)
}

但最好将其放入 struct 或 class 中以避免污染全局命名空间。

(另外，我不确定你为什么使用 NSDate ...我建议保留 Date 对象。)

<小时/>

就我个人而言，我会做这样的事情:

class TimerManager {
    var releaseDate: Date?

    private weak var countdownTimer: Timer?

    private let formatter: DateComponentsFormatter = {
        let formatter = DateComponentsFormatter()
        formatter.unitsStyle = .full
        formatter.allowedUnits = [.day, .hour, .minute, .second]
        return formatter
    }()

    deinit {
        countdownTimer?.invalidate()
    }

    func startTimer() {
        releaseDate = DateComponents(calendar: .current, year: 2019, month: 2, day: 23, hour: 8).date

        countdownTimer = Timer.scheduledTimer(withTimeInterval: 1, repeats: true) { [weak self] _ in
            self?.updateTime()
        }
    }

    private func updateTime() {
        guard let releaseDate = releaseDate,
            let string = formatter.string(from: Date(), to: releaseDate) else { return }
        print(string)
    }
}

这不仅可以解决Timer问题，还可以让您摆脱手动构建日期差异组件的格式化字符串的麻烦。