Swift 停止在主线程上运行的DispatchQueue

我有一段代码：

    DispatchQueue.main.asyncAfter(deadline: .now() + (delay * Double(isDelayAccounted.hashValue)) + extraDelay) {
        self.isShootingOnHold = false
        self.shoot()
        self.shootingEngine = Timer.scheduledTimer(timeInterval: (Double(60)/Double(self.ratePerMinute)), target: self, selector: #selector(ShootingEnemy.shoot), userInfo: nil, repeats: true)   
    }

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现在，我希望能够阻止这个线程执行。我怎样才能阻止它被执行？例如，3秒钟后，我决定不再执行它，所以我想停止它。

您可以使用

DispatchWorkItem

s。它们可以在调度队列上调度，并在执行之前取消

let work = DispatchWorkItem(block: {
    self.isShootingOnHold = false
    self.shoot()
    self.shootingEngine = Timer.scheduledTimer(timeInterval: (Double(60)/Double(self.ratePerMinute)), target: self, selector: #selector(ShootingEnemy.shoot), userInfo: nil, repeats: true)
})
DispatchQueue.main.asyncAfter(deadline: .now() + (delay * Double(isDelayAccounted.hashValue)) + extraDelay, execute: work)
work.cancel()

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您可以使用一次性的

DispatchSourceTimer

而不是

asyncAfter

var oneShot : DispatchSourceTimer!

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并用

oneShot?.cancel()
oneShot = nil

可以使块无效

oneShot?.cancel()
oneShot = nil