延迟循环（倒数计时功能） [英] Delaying the loop (countdown func)

问题描述

我看了很多文章，没有一个答案是正确的。我知道这些方法有效，但是在for循环中却无效。如何创建倒计时功能-在其中可以延迟一秒打印数组。

I've looked at many articles, none of the answers are correct. I know that these methods work, but inside a for-loop they don't. How can I create a countdown func - where I can print an array with a one second delay in between.

let array = [9, 8, 7, 6, 5, 4, 3, 2, 1]

我尝试过：

for n in array {
            DispatchQueue.main.asyncAfter(deadline: .now() + 1) {
                print(n)
            }
        }

它会打印1秒后所有数字。因此，我尝试了以下操作：

And it prints all the numbers after 1 second. So I tried this:

override func viewDidLoad() {
    super.viewDidLoad()
let timer = Timer.scheduledTimer(timeInterval: 2, target: self, selector: (#selector(printer)), userInfo: nil, repeats: true)
}

@objc func printer() {
    for n in array {
       print(n)
        }
    }

相同的结果。我猜这些是好的方法，但是出了点问题。

Same result. I guess these are good methods, but something's wrong.

推荐答案

为计时器创建一个计数器变量和另一个变量

Create a counter variable and another variable for the timer

var counter = 0
var timer : Timer?

在 viewDidLoad 中创建计时器

override func viewDidLoad() {
    super.viewDidLoad()
    timer = Timer.scheduledTimer(timeInterval: 1.0, target: self, selector: #selector(printer), userInfo: nil, repeats: true)
}

在操作方法中，增加 counter 变量，如果达到数组中的项目数，则使计时器无效。

In the action method increment the counter variable and invalidate the timer if the number of items in the array is reached.

@objc func printer() {

    print(array[counter])
    counter += 1
    if counter == array.count {
       timer?.invalidate()
       timer = nil
    }
}

另一种方法是 DispatchSourceTimer ，它避免了 @objc 运行时

Another way is DispatchSourceTimer, it avoids the @objc runtime

var timer : DispatchSourceTimer?

let interval : DispatchTime = .now() + .seconds(1)

timer = DispatchSource.makeTimerSource(queue: DispatchQueue.global())
timer!.schedule(deadline:interval, repeating: 1)
var index = 0
timer!.setEventHandler {
    // DispatchQueue.main.async {
       print(array[index])
    }
    index += 1
    if index == array.count {
        timer!.cancel()
        timer = nil
    }
}
timer!.resume()

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