Question

以下代码在延迟后不会打印你好。

有什么不对吗？

 func delay(seconds delay:Int, closure:@escaping ()->()) {

    DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + .seconds(delay)) {
        closure()
    }
}

delay(seconds: 5) { 
    print("hello")
}

Answer 1

我通过创建一个runloop来实现它，否则程序只是退出而不调用异步块。如果您正在为iOS应用程序开发，则不应该这样做。

var keepAlive = true

   func delay(seconds delay:Int, closure:@escaping ()->()) {

        DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + .seconds(delay)) {
        closure()
        }
    }


   delay(seconds: 5) { 
        print("hello")
        keepAlive = false
    }

let runLoop = RunLoop.current
while keepAlive && runLoop.run(mode: .defaultRunLoopMode, before: Date(timeIntervalSinceNow: 0.1)) {}

Answer 2

let delayInSeconds = 5.0

DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + delayInSeconds) {

print("hello")

}

在swift 3中创建代码块的延迟

2 个答案: