ios - iOS 中另一个请求中的 HTTP 请求

Question

我需要在另一个请求中执行 HTTP 请求，据我所知，这需要同步。
在本例中，我获取“帖子”数组并获取有关它们的信息。
这是代码，可以帮助您更好地了解情况:

// getPosts()
...
let task = NSURLSession.sharedSession().dataTaskWithRequest(request, completionHandler: { (data: NSData!, response: NSURLResponse?, error: NSError?) -> Void in
    if response != nil {
        let dataDictionary = NSJSONSerialization.JSONObjectWithData(data!, options: NSJSONReadingOptions.MutableContainers, error: &err) as [NSDictionary]     
        for postDic: NSDictionary in dataDictionary {
           let post = Post(postId: postDic["post_id"] as String)

           post.likes = postDic["likes"] as String
           post.views = postDic["views"] as String

           self.getCommentCountForPostID(post.postId, completion: { (count) -> Void in
               post.comments = count
           })

           ...
           self.posts.addObject(post)
        }
        // reloading table view etc
    }
})
task.resume()

这是函数getCommentCountForPostID:

func getCommentCountForPostID(postID: String, completion: ((count : String?) -> ())) {
    ...
    let task = NSURLSession.sharedSession().dataTaskWithRequest(request, completionHandler: { (data: NSData!, response: NSURLResponse?, error: NSError?) -> Void in
        if response != nil {
            let resultCount: NSString! = NSString(bytes: data.bytes, length: data.length, encoding: NSASCIIStringEncoding)
            print(resultCount)

            completion(count: resultCount)
        }

    })

    task.resume()
}

问题是 getCommentCountForPostID 函数在 for 循环向前运行时异步调度。我需要该函数首先完成评论请求，然后才继续执行 getPosts()。我尝试过使用 dispatch_sync() 将不同部分包装在代码中的多种组合，但没有成功。
我怎样才能实现这个目标？非常感谢!

Answer 1

使用递归来达到您的目的。

加载第一篇文章 -> 处理它 -> 加载下一篇文章 -> 当所有文章加载完毕后完成。

我创建了名为“loopAndLoad”的辅助方法，它将您的数据数组作为参数，以及要处理的当前项目的索引

let task = NSURLSession.sharedSession().dataTaskWithRequest(request, completionHandler: { (data: NSData!, response: NSURLResponse?, error: NSError?) -> Void in
            if response != nil {
                let dataDictionary = NSJSONSerialization.JSONObjectWithData(data!, options: NSJSONReadingOptions.MutableContainers, error: &err) as [NSDictionary]
                self.loopAndLoad(0, dataDictionary);
            }
        })
        task.resume()



    func loopAndLoad( index: Int, dataArray: Array<NSDictionary>)
    {
        let postDic = dataArray[index]
        let post = Post(postId: postDic["post_id"] as String)

        post.likes = postDic["likes"] as String
        post.views = postDic["views"] as String

        self.getCommentCountForPostID(post.postId, completion: { (count) -> Void in
            post.comments = count
            self.posts.addObject(post)
            if (++index < dataArray.count)
            {
                self.loopAndLoad(index, dataArray)
            }
            else
            {
                /// end of loop
            }
        })
    }


    func getCommentCountForPostID(postID: String, completion: ((count : String?) -> ())) {
        ...
        let task = NSURLSession.sharedSession().dataTaskWithRequest(request, completionHandler: { (data: NSData!, response: NSURLResponse?, error: NSError?) -> Void in
            if response != nil {
                let resultCount: NSString! = NSString(bytes: data.bytes, length: data.length, encoding: NSASCIIStringEncoding)
                print(resultCount)

                completion(count: resultCount)
            }

        })

        task.resume()
    }