如何异步调用api并在成功时更新UI？

Question

我想知道什么是正确的设计：

1. 进行API调用
2. 创建结果模型
3. 加载模型的图像
4. 等待加载所有内容..然后更新ui

我使用（嵌套）委派和 dispatch_group 。但我相信，你可能会有一些提示如何做到这一点，不是吗？

这是我的工作代码：

查看控制器

@IBAction func loadLoaction(sender: AnyObject) {
    placeManager.loadRandomLoaction(lat, longitude: long)
}

func placeDidLoad(place: Place) {
    nameLabel.text = place.name
    imageView.image = place.image
}

类

import Foundation
import Alamofire

extension Alamofire.Request {
    class func imageResponseSerializer() -> Serializer {
        return { request, response, data in
            if data == nil {
                return (nil, nil)
            }

            let image = UIImage(data: data!, scale: UIScreen.mainScreen().scale)

            return (image, nil)
        }
    }

    func responseImage(completionHandler: (NSURLRequest, NSHTTPURLResponse?, UIImage?, NSError?) -> Void) -> Self {
        return response(serializer: Request.imageResponseSerializer(), completionHandler: { (request, response, image, error) in
            completionHandler(request, response, image as? UIImage, error)
        })
    }
}

public protocol PlaceDelegate: class {
    func placeDidLoad(place: Place)
}

public class Place : NSObject {

    var delegate: PlaceDelegate?

    public var name: String?
    public var category: String?
    public var image_url: String?
    public var snippet_text: String?
    public var address: String?
    public var distance: String?
    public var url: String?
    public var image: UIImage = UIImage()

    var dispatch_group = dispatch_group_create()

    init(fromResponseDict responseDict: Dictionary<String, String>, delegate: PlaceDelegate) {
        self.delegate = delegate

        // Set props
        self.name = responseDict["name"] 
        self.category = responseDict["category"]
        self.image_url = responseDict["image_url"]!
        self.snippet_text = responseDict["snippet_text"]
        self.url = responseDict["url"]
        self.address = responseDict["address"]!

        super.init()

        // Load image
        self.loadImage()

        // Dispatch if success
        dispatch_group_notify(self.dispatch_group, dispatch_get_main_queue(), {                
            self.delegate?.placeDidLoad(self)
        })


    }

    // (3) Load the image        
    func loadImage() {
        dispatch_group_enter(self.dispatch_group);           

        var request:Alamofire.Request = Alamofire.request(.GET, self.image_url!).responseImage() {
            (request, _, image, error) in
            if error == nil && image != nil {
                NSLog("imageRequestSuccess")

                self.image = image!

                // Dispatch if success
                dispatch_group_leave(self.dispatch_group)
            } else {
                NSLog("imageRequestFailure")

                // Dispatch also to handle failure
                dispatch_group_leave(self.dispatch_group)
            }
        }
    }
}


public protocol PlaceManagerDelegate: class {
    func placeDidLoad(place: Place)
}

public class PlaceManager : NSObject, PlaceDelegate {

    public weak var delegate: PlaceManagerDelegate?

    var isLoading = false

    enum Router: URLRequestConvertible {
        static let baseURLString = "http://api.domain.com"

        // Endpoints
        case RandomPlace(lat:Double, long:Double)

        var URLRequest: NSURLRequest {
            let (path: String, parameters: [String: AnyObject]) = {
                switch self {
                case .RandomPlace (let lat, let long):
                    let params : [ String : AnyObject] = ["ll": "\(lat),\(long)", "", "debug":"true"]
                    return ("/getRandomLocation", params)
                }
            }()

            let URL = NSURL(string: Router.baseURLString)
            let URLRequest = NSURLRequest(URL: URL!.URLByAppendingPathComponent(path))
            let encoding = Alamofire.ParameterEncoding.URL

            return encoding.encode(URLRequest, parameters: parameters).0
        }
    }

    public func loadRandomLoaction(latitude:Double, longitude:Double) {

        if isLoading {
            return
        }

        isLoading = true

        // (1) Make the API Call 
        Alamofire.request(PlaceManager.Router.RandomPlace(lat: latitude, long: longitude)).responseJSON() {
            (_, _, JSON, error) in

            if error == nil {

                dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0)) {

                    if let responseDict = JSON as? Dictionary<String, String> {
                        // (2) Create the model  
                        let place = Place(fromResponseDict: responseDict, delegate:self)
                    }                        
                }
            } else {
                NSLog(error!.localizedDescription)
            }
            self.isLoading = false
        }
    }

    // (4) Update the UI
    public func placeDidLoad(place: Place) {
        self.delegate?.placeDidLoad(place)
    }

}