我是C＃开发人员转换为Swift tvOs并开始学习。我已经取得了一些进展，但不知道如何处理对json的嵌套调用。来自不同的提供商，所以我不能只是组合查询。
我如何等待内部请求完成，以便TVSeries有poster_path？有没有更好的方法将节目添加到集合中，然后在另一个线程中处理海报路径加载，这样就不会延迟UI体验？
func downloadTVData() {
let url_BTV = NSURL(string: BTV_URL_BASE)!
let request_BTV = NSURLRequest(URL: url_BTV)
let session_BTV = NSURLSession.sharedSession()
//get series data
let task_BTR = session_BTV.dataTaskWithRequest(request_BTV) { (data_BTV, response_BTV, error_BTV) -> Void in
if error_BTV != nil {
print (error_BTV?.description)
} else {
do {
let dict_BTV = try NSJSONSerialization.JSONObjectWithData(data_BTV!, options: .AllowFragments) as? Dictionary<String, AnyObject>
if let results_BTV = dict_BTV!["results"] as? [Dictionary<String, AnyObject>]{
for obj_BTV in results_BTV {
let tvshow = TVSeries(tvDict: obj_BTV)
//for each tv series try to load a poster_path from secondary provider
if let str = obj_BTV["title"] as? String!{
let escapedString = str?.stringByAddingPercentEncodingWithAllowedCharacters(.URLQueryAllowedCharacterSet())!
if let url = NSURL(string: self.SEARCH_URL_BASE + escapedString!) {
let request = NSURLRequest(URL: url)
let session = NSURLSession.sharedSession()
let task = session.dataTaskWithRequest(request) { (data, response, error) -> Void in
if error != nil {
print (error?.description)
} else {
do {
let dict = try NSJSONSerialization.JSONObjectWithData(data!, options: .AllowFragments) as? Dictionary<String, AnyObject>
if let results = dict!["results"] as? [Dictionary<String, AnyObject>] {
//iterate through the poster array
for obj in results {
if let path = obj["poster_path"] as? String {
tvshow.posterPath = path
break
}
}
}
} catch let error as NSError {
print(error.description)
}
}
}
task.resume()
}
}
self.tvSeries.append(tvshow)
}
dispatch_async(dispatch_get_main_queue()){
self.collectionView.reloadData()
}
}
} catch let error as NSError {
print(error.description)
}
}
}
task_BTR.resume()
}
感谢您的帮助！
答案 0 :(得分：1)
我建议将事物拆分为多个方法，使用回调来对操作进行排序，并利用Swift的内置throws错误处理机制。这是一个例子，并不完美，但可能有助于作为一个起点：
class TVSeries
{
let title: String
var posterPath: String?
enum Error: ErrorType {
case MalformedJSON
}
init(tvDict: [String: AnyObject]) throws
{
guard let title = tvDict["title"] as? String else {
throw Error.MalformedJSON
}
self.title = title
}
static func loadAllSeries(completionHandler: [TVSeries]? -> Void)
{
NSURLSession.sharedSession().dataTaskWithURL(NSURL(string: BTV_URL_BASE)!) { data, response, error in
guard let data = data else {
print(error)
completionHandler(nil)
return
}
do {
completionHandler(try fromJSONData(data))
}
catch let error {
print(error)
}
}.resume()
}
static func fromJSONData(jsonData: NSData) throws -> [TVSeries]
{
guard let dict = try NSJSONSerialization.JSONObjectWithData(jsonData, options: .AllowFragments) as? [String: AnyObject] else {
throw Error.MalformedJSON
}
guard let results = dict["results"] as? [[String: AnyObject]] else {
throw Error.MalformedJSON
}
return try results.map {
return try TVSeries(tvDict: $0)
}
}
func loadPosterPath(completionHandler: () -> Void)
{
guard let searchPath = title.stringByAddingPercentEncodingWithAllowedCharacters(.URLQueryAllowedCharacterSet()) else {
completionHandler()
return
}
let url = NSURL(string: SEARCH_URL_BASE)!.URLByAppendingPathComponent(searchPath)
NSURLSession.sharedSession().dataTaskWithURL(url) { [weak self] data, response, error in
defer { completionHandler() }
guard let strongSelf = self else { return }
guard let data = data else {
print(error)
return
}
do {
strongSelf.posterPath = try TVSeries.posterPathFromJSONData(data)
}
catch let error {
print(error)
}
}.resume()
}
static func posterPathFromJSONData(jsonData: NSData) throws -> String?
{
guard let dict = try NSJSONSerialization.JSONObjectWithData(jsonData, options: .AllowFragments) as? [String: AnyObject] else {
throw Error.MalformedJSON
}
guard let results = dict["results"] as? [[String: AnyObject]] else {
throw Error.MalformedJSON
}
for result in results {
if let path = result["poster_path"] as? String {
return path
}
}
return nil
}
}