ios - 数据乱序

Question

我正在使用 Flickr API 获取集合中的所有相册，然后使用相册 ID 从中获取每个相册的主照片。它有效，但照片没有按顺序返回给我，因此每个相册的主照片与我收藏 View 中的相册标题不匹配。

func getPhotoCollection() {
        let collectionURLString = "https://api.flickr.com/services/rest/?method=flickr.collections.getTree&api_key={API_KEY}&collection_id=72157676119666248&user_id={USER_ID}&format=json&nojsoncallback=1"

        self.session = URLSession(configuration: .default, delegate: self, delegateQueue: nil)
        let task = self.session?.dataTask(with: URL(string: collectionURLString)!, completionHandler: { (data, response, error) in
            let json = self.getJSONFrom(urlString: collectionURLString)
            let collections = json["collections"]
            let collection = collections["collection"].arrayObject as! [[String:AnyObject]]
            for collectionObject in collection {
                let sets = collectionObject["set"] as! [[String: AnyObject]]
                for set in sets {
                    let albumId = set["id"] as! String
                    let albumTitle = set["title"] as! String
                    self.albumIds.append(albumId)
                    self.albumTitles.append(albumTitle)
                }
            }

            self.getAlbumPrimary()
        })

        task?.resume()
    }

func getAlbumPrimary() {
        for albumId in self.albumIds {
            let apiURLString = "https://api.flickr.com/services/rest/?method=flickr.photosets.getPhotos&api_key={API_KEY}&photoset_id=\(albumId)&per_page=1&user_id={USER_ID}&format=json&nojsoncallback=1"

            self.session = URLSession(configuration: .default, delegate: self, delegateQueue: nil)
            let task = self.session?.dataTask(with: URL(string: apiURLString)!, completionHandler: { (data, response, error) in
                let json = self.getJSONFrom(urlString: apiURLString)
                let photos = json["photoset"]
                let photo = photos["photo"].arrayObject as! [[String:AnyObject]]
                let primaryPic = photo[0]
                let farm = primaryPic["farm"] as! Int
                let server = primaryPic["server"] as! String
                let picId = primaryPic["id"] as! String
                let secret = primaryPic["secret"] as! String

                let urlString = String(format: "https://farm%d.static.flickr.com/%@/%@_%@_b.jpg", farm, server, picId, secret)
                self.albumPrimaryURLs.append(urlString)

                DispatchQueue.main.async {
                    self.collectionView.reloadData()
                    self.loaded = true
                }
            })

            task?.resume()
        }
    }

Answer 1

这是多个异步任务的工作方式(无序)，您需要创建一个模型而不是单独的数组然后从数据加载以填充最后一个属性

class Item {
  let id,title:String
  var url:String?
  init(id:String,title:String){
   self.id = id
   self.title = title 
  }
  func loadUrl(completion:@escaping () -> () ) {
     // here load and set the url
  }
}

---

var items = [Item]() // declare main array 

 let albumId = set["id"] as! String
 let albumTitle = set["title"] as! String 
 let item = Item(id:albumId,title:albumTitle)
 self.items.append(item) 

最后加载集合

let g = DispatchGroup()
items.forEach {
   g.enter()
   $0.loadUrl {
      g.leave()
   }
} 
g.notify(queue:.main) {
  self.collectionView.reloadData()
  self.loaded = true
}