使用 Alamofire 的同步请求答案

【问题标题】：Synchronous request using Alamofire使用 Alamofire 的同步请求
【发布时间】：2018-08-17 16:45:59
【问题描述】：

我检查了其他解决方案，例如 How to make a synchronous request using Alamofire?，我按照所有说明进行操作，但我无法完成请求并使用这些信息。

我需要从谷歌地图中检索距离和路线点，然后使用该信息完成一个数组。这是函数：

func getGoogleMapsInfo(startLocation: CLLocationCoordinate2D, restaurant: Customer, completion: @escaping (_ distance: Int, _ routePoints: String)  -> ()){

    let endLocation = CLLocationCoordinate2D(latitude: restaurant.latitude, longitude: restaurant.longitude)
    let origin = "\(startLocation.latitude),\(startLocation.longitude)"
    let destination = "\(endLocation.latitude),\(endLocation.longitude)"
    var distance = 0
    var routePoints = ""

    let url = "https://maps.googleapis.com/maps/api/directions/json?origin=\(origin)&destination=\(destination)&mode=walking"
    Alamofire.request(url).responseJSON { response in

        switch response.result {
        case .success:

            do {
                self.json = try JSON(data: response.data!)

                distance = Int(truncating: self.json["routes"][0]["legs"][0]["distance"]["value"].numberValue)


                let route = self.json["routes"].arrayValue.first
                let routeOverviewPolyline = route!["overview_polyline"].dictionary
                routePoints = (routeOverviewPolyline?["points"]?.stringValue)!
                completion(distance, routePoints)
                break
            } catch {
                print("error JSON")
            }


        case .failure(let error):
            print(error)
            completion(distance, routePoints)
            break
        }

    }


}

这就是我所说的：

    for index in 0...nearbyRestaurants.count - 1 {

        getGoogleMapsInfo(startLocation: currentLocation, restaurant: nearbyRestaurants[index]) { (distance, routePoints) in
            nearbyRestaurants[index].distance = distance
            nearbyRestaurants[index].routePoints = routePoints
        }

    }

如果有人可以帮助我，我将不胜感激。

【问题讨论】：

"检查了其他解决方案，例如如何使用 Alamofire 发出同步请求？"不要检查它们。永远永远永远永远不会同步网络。绝不。我有没有提到过？
@matt 同步网络请求可以来自后台线程。
@Cristik 我有没有提到“除非你已经在后台线程上”？
@matt 我可能在某处看到过 :)

标签： swift alamofire

【解决方案1】：

不要尝试使异步请求同步

改为使用DispatchGroup,notify 在所有网络请求完成后调用。

let group = DispatchGroup()
for index in 0..<nearbyRestaurants.count {
    group.enter()
    getGoogleMapsInfo(startLocation: currentLocation, restaurant: nearbyRestaurants[index]) { (distance, routePoints) in
        nearbyRestaurants[index].distance = distance
        nearbyRestaurants[index].routePoints = routePoints
        group.leave()
    }
}
group.notify(queue: DispatchQueue.main) {
        print("all info data has been received")
}

【讨论】：