swift - Alamofire for 循环在 Playgrounds 中返回空数组

Question

我搜索了最后一个小时，但似乎无法弄清楚。我认输并询问。

我在下面有以下 playground 脚本，它打印了一个空数组。

我想在函数被调用时返回一个自定义对象数组。我读到 Alamofire 是异步的，但我现在真的不知道该怎么做。

提前致谢!

//: Playground - noun: a place where people can play

import UIKit
import Alamofire
import SWXMLHash
import PlaygroundSupport
import Foundation


PlaygroundPage.current.needsIndefiniteExecution = true
URLCache.shared = URLCache(memoryCapacity: 0, diskCapacity: 0, diskPath: nil)

class Tram {

    var arrivalInMinutes: Int?
    var tramDestinationEnglish: String?

    init(destination: String, arrivalTime: Int) {
        tramDestinationEnglish = destination
        arrivalInMinutes = arrivalTime

    }
}

func retrieveListOfTrams() -> [Tram] {

    var anyArray = [Tram]()

    Alamofire.request("https://hktramways.com/nextTram/geteat.php?stop_code=08W")
        .response { (response) in

            let xmlData = SWXMLHash.parse(response.data!)

            for elem in xmlData["root"]["metadata"].all {
                let tramArrival = elem.element!.attribute(by: "arrive_in_minute")!.text
                let tramDestination = elem.element!.attribute(by: "tram_dest_en")!.text
                anyArray.append(Tram(destination: tramDestination, arrivalTime: Int(tramArrival)!))

                }

            }
    return anyArray


}

print(retrieveListOfTrams())

Answer 1

问题是您在请求返回结果之前返回了数组，因为当您阅读 Alamofire 时，它​​具有异步行为。解决这个问题的一种方法是使用一个完成 block ，它只会在结果到达后返回数组:

func retrieveListOfTrams(completion: @escaping ([Tram]) -> Void) {

    var anyArray = [Tram]()

    Alamofire.request("https://hktramways.com/nextTram/geteat.php?stop_code=08W")
        .response { (response) in

            let xmlData = SWXMLHash.parse(response.data!)

            for elem in xmlData["root"]["metadata"].all {
                let tramArrival = elem.element!.attribute(by: "arrive_in_minute")!.text
                let tramDestination = elem.element!.attribute(by: "tram_dest_en")!.text
                anyArray.append(Tram(destination: tramDestination, arrivalTime: Int(tramArrival)!))

                }


            completion(anyArray)
            }   

}

然后就可以调用函数了:

retrieveListOfTrams(completion: { anyArray in
    print(anyArray.description)
})