ios - 如何使用viewdidload()中的回调函数？

Question

我得到了一个带有函数(requestSitesData)的类(Client)，它可以从服务器获取数据，并且其中有@escaping:

func requestSitesData(response: @escaping (_ data: Data?, _ error: Error?) -> Void) {
        DispatchQueue.global(qos: .default).asyncAfter(deadline: .now() + randomTimeDelay()) {
            guard self.isRequestSuccessful() else {
                response(nil, ClientError.requestFailed)

                return
            }
            guard let fileURL = Bundle.main.url(forResource: self.responseFilename, withExtension: "json") else {
                response(nil, ClientError.noFile)
                return 
            }
            do {
                let data = try Data(contentsOf: fileURL)
                let _ = try JSONSerialization.jsonObject(with: data)
                response(data, nil)
            } catch let error {
                response(nil, error)
            }
        }
    }

所以我认为这里的响应函数是一个回调函数。在我的项目中，我有一个全局变量来存储来自服务器的数据，并希望将其显示在我的 View Controller 上。但似乎无论我将 call_back 函数放在 viewcontroller 类中的哪个位置，回调函数都会在所有函数之后调用(应该如此)，所以我无法在 viewdidload() 中获取数据。

func call_back(data: Data?, error: Error?) -> Void {
        print("call_back called")
        if let file_data = data {
            if let sites_map = try? JSONSerialization.jsonObject(with: file_data, options: .mutableLeaves) as! [String: [Dictionary<String, Any>]] {
                if let sites = sites_map["sites"] {
                    for site in sites {
                        if let name = site["name"] as? String,
                        let slogan = site["slogan"] as? String,
                        let url = site["url"] as? String,
                        let description = site["description"] as? String,
                        let color = site["color"] as? String {
                            let single_site: Site = Site(name: name, slogan: slogan, url: url, description: description, color: color)
                            sites_res.append(single_site)
                        }
                    }
                }
            }
        }
    }

override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        let c = Client()
        c.requestSitesData { (response_data, response_error) in
            self.call_back(data: response_data, error: response_error)
            print("ddd")
        }

    }

我不知道viewdidload()中如何获取数据，是不是因为我调用这个call_back函数的方式不对？谁能帮忙？

Answer 1

修改函数如下:

func call_back(data: Data?, error: Error?) -> [String: [Dictionary<String, Any>]]? {
            print("call_back called")
            if let file_data = data {
                if let sites_map = try? JSONSerialization.jsonObject(with: file_data, options: .mutableLeaves) as? [String: [Dictionary<String, Any>]] {
                    return sites_map
                }
            }
            return nil
        }


override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        let c = Client()
        c.requestSitesData { (response_data, response_error) in
            if let sites_map = self.call_back(data: response_data, error: response_error){
        if let sites = sites_map["sites"] {
            for site in sites {
                if let name = site["name"] as? String,
                    let slogan = site["slogan"] as? String,
                    let url = site["url"] as? String,
                    let description = site["description"] as? String,
                    let color = site["color"] as? String {
                    let single_site: Site = Site(name: name, slogan: slogan, url: url, description: description, color: color)
                    sites_res.append(single_site)
                }
            }
        }
    }
  }
}