Swift class 内的计时器未按预期工作

Question

我很难理解为什么 Timer 在 class 之外工作，但在内部却不行。我认为它与范围有关，但找不到任何有助于我理解问题的资源。

这是我的游乐场代码：

import UIKit
import Dispatch

// Timer inside a class
print ("\nStarting Class based Timer Section\n")

class mytest {
    
    init () {
        print ("mytest Classs init()")
    }
    
    func starttimer(){
        print ("mytest Classs starttimer()")
        let timer = DispatchSource.makeTimerSource()
        timer.setEventHandler() {
            self.doIt()
            print ("y")
        }
        timer.schedule(deadline: .now(), repeating: 1, leeway: .nanoseconds(1))
        timer.activate()
    }
        
    func doIt() {
        let wherefrom = "Inside"
        print( "\(wherefrom) of Class")
    }
}

var tst = mytest()
tst.starttimer()




// Stand alone timer works outside of a class
print ("\nStarting Stand alone Timer Section\n")

func doIt(){
    let wherefrom = "Outside"
    print( "\(wherefrom) of Class")
}

let timer = DispatchSource.makeTimerSource()
timer.setEventHandler() {
    doIt()
    print ("x")
}
timer.schedule(deadline: .now(), repeating: 1, leeway: .nanoseconds(1))
timer.activate()

Answer 1

计时器仅作为局部变量存在，因此一旦 starttimer 函数完成，计时器就会消失。

将它作为属性添加到 class 以保留它

class mytest {
    var timer: DispatchSourceTimer?
    init () {
        print ("mytest Classs init()")
    }

    func starttimer(){
        print ("mytest Classs starttimer()")
        timer = DispatchSource.makeTimerSource()
        timer?.setEventHandler() {
            self.doIt()
            print ("y")
        }
        timer?.schedule(deadline: .now(), repeating: 1, leeway: .nanoseconds(1))
        timer?.activate()
    }

    func doIt() {
        let wherefrom = "Inside"
        print( "\(wherefrom) of Class")
    }
}

Swift class 内的计时器未按预期工作

Swift Timer inside class not working as expected

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