如何在Swift中进行异步/等待? [英] How to make async / await in Swift?

问题描述

我想模拟从Javascript到Swift 4的异步和等待请求.我搜索了很多有关如何做的方法，我以为我找到了DispatchQueue的答案，但我不知道它是如何工作的.

I would like to simulate async and await request from Javascript to Swift 4. I searched a lot on how to do it, and I thought I found the answer with DispatchQueue, but I don't understand how it works.

我想做一个简单的事情:

I want to do a simple stuff:

if let items = result.value {
    var availableBornes = [MGLPointFeature]()

    for item in items {
        guard let id = item.id else { continue }

        let coordinate = CLLocationCoordinate2D(latitude: Double(coor.x), longitude: Double(coor.y))

        // ...

        // This is an asynchronous request I want to wait
        await _ = directions.calculate(options) { (waypoints, routes, error) in
            guard error == nil else {
                print("Error calculating directions: \(error!)")
                return
            }

            // ...

            if let route = routes?.first {
                let distanceFormatter = LengthFormatter()
                let formattedDistance = distanceFormatter.string(fromMeters: route.distance)
                item.distance = formattedDistance

                // Save feature
                let feature = MGLPointFeature()

                feature.attributes = [
                    "id": id,
                    "distance": formattedDistance
                ]

                availableBornes.append(feature)

            }
        }
    }

    // This should be called after waiting for the async requests
    self.addItemsToMap(availableBornes: availableBornes)
}

我该怎么办?

推荐答案

感谢 vadian 的评论，我发现我所期望的，而且非常容易.我使用DispatchGroup()，group.enter()，group.leave()和group.notify(queue: .main){}.

Thanks to vadian's comment, I found what I expected, and it's pretty easy. I use DispatchGroup(), group.enter(), group.leave() and group.notify(queue: .main){}.

func myFunction() {
    let array = [Object]()
    let group = DispatchGroup() // initialize

    array.forEach { obj in

        // Here is an example of an asynchronous request which use a callback
        group.enter() // wait
        LogoRequest.init().downloadImage(url: obj.url) { (data) in
            if (data) {
                group.leave() // continue the loop
            }
        }
    }

    group.notify(queue: .main) {
        // do something here when loop finished
    }
}

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