好吧，我非常想知道这一点。我在用户名数组中有用户名。我试图做一个查询，我根据用户名数组中的顺序对结果进行排序。我尝试使用NSSortDescriptor，但我认为它不能完成此任务。谢谢

func photoQuery () {
    let descriptor: NSSortDescriptor = NSSortDescriptor(key: "usernameArray",ascending: false)
    let photoQuery = PFQuery(classname: "UserPhoto")
    photoQuery.whereKey("username",containedIn: usernameArray)
    photoQuery.order(by: descriptor)
    photoQuery.findObjectsInBackground(block: { (objects: [PFObject]?,error: Error?) in
        if let objects = objects {
            for object in objects {
                if error == nil {
                    let userImageFile = object["photo"] as? PFFileObject
                    let urlString = userImageFile?.url as! String
                    if let url = URL(string: urlString) {
                        let data = try? Data(contentsof: url)
                        if let imageData = data {
                            self.urlArray.append(urlString as NSString)
                            self.cache.setObject(UIImage(data:imageData)!,forKey: urlString as NSString)

                        }
                    }
                }
            }
        }
    })
}