Swift，在返回列表之前等待两个完成 block 完成

Question

我试图调出两个返回一些 json 的独立 api 端点，这两个调用将对象添加到列表中...我如何等待两个函数完成，然后再将列表返回给 View Controller

import Alamofire
import SwiftyJSON

class SearchService {

var searchItemList = [SearchItem]()

func performFetch(keyword: String, count: Int, completion:(items: [SearchItem]?) -> ()){
    >>>// NEED TO WAIT FOR THE fetchItemsA AND fetchItemsB TO FINISH THEM RETURN ‘searchItemList’
}

func fetchItemsA(keyword: String, count: Int, completion:(error:NSError?) -> ())  {
    guard let url = self.searchUrl else {
        return
    }

    let manager = Manager.sharedInstance
        manager.request(.GET, url, parameters: ["keywords": keyword, "count": count], encoding: ParameterEncoding.URL)
            .validate()
            .responseJSON {response in

        …

        for item in items {
            self.searchItemList.append(SearchItem(json: item)!)
        }

        …
        completion(error: resultError)
}

func fetchItemsB(keyword: String, count: Int, completion:(error:NSError?) -> ())  {
    guard let url = self.searchUrl else {
        return
    }

        let manager = Manager.sharedInstance
            manager.request(.GET, url, parameters: ["keywords": keyword, "count": count], encoding: ParameterEncoding.URL)
            .validate()
            .responseJSON {response in

    …

    for item in items {
        self.searchItemList.append(SearchItem(json: item)!)
    }

    …
            completion(error: resultError)
    }
}

感谢任何帮助

Answer 1

如果 API 不同，您可以尝试 this answer .如果您想执行两个异步请求，最简单的解决方案是对请求进行计数并检查已完成的请求数(答案中的第一个解决方案)。请记住，响应可能是成功或错误。