同步嵌套的异步任务

我有嵌套的异步任务。下面这个流程的函数：loadEpisodes（加载剧集列表） - >使用完成的数组遍历每集第一集，并为特定情节加载注释（多一个异步任务）。同步嵌套的异步任务

问题是：comletion（fullyEpisodes）在完成注释加载任务之前执行。我试图使用Dispatch Group（第二代码块），但它不工作。

func loadComments(comletion: @escaping ([Episode]) -> Void){ 
loadEpisodes(completion: { 
    episodes in 
    var fullyEpisodes = [Episode]() 
    for episode in episodes { 
     WebService().load(resource: episode.comment, comletion: { 
      comments in 
      if let comments = comments { 
       let _episode = Episode(id: episode.id, title: episode.title, comments: comments) 
       fullyEpisodes.append(_episode) 
       print("done") 
      } 
     }) 
    } 
    comletion(fullyEpisodes) 

}) 
}

实现了调度组：

func loadComments(comletion: @escaping ([Episode]) -> Void){ 
    loadEpisodes(completion: { 
     episodes in 
     var fullyEpisodes = [Episode]() 
     let group = DispatchGroup() 
     for episode in episodes { 
      group.enter() 
      WebService().load(resource: episode.comment, comletion: { 
       comments in 
       if let comments = comments { 
        let _episode = Episode(id: episode.id, title: episode.title, comments: comments) 
        fullyEpisodes.append(_episode) 
        print("done") 
       } 
      }) 
      group.leave() 
     } 
     group.wait() 
     group.notify(queue: .main, execute: { 
      comletion(fullyEpisodes) 
     }) 

    }) 
}

当我试图通过“打印更换评论加载请求（”东西“）”（不是一个新的异步任务），调度组工作。

来源

2016-12-02 The Bao

觉得你的意思'盛大中央dispatch'不'最大，共divisor';） –

@JacobKing：哎呀！我设置了错误的标签。感谢：D –

是的，令人讨厌的是，指定gcd标签将其替换为“最大公约数”（尽管关于大中央调度的堆栈溢出问题比最大公约数要多得多）。见http://meta.stackoverflow.com/q/251143/1271826或http://meta.stackexchange.com/questions/165133/propose-significant-change-in-the-definition-of-gcd-tag – Rob

在第二个示例中，（a）将group.leave()移动到load()完成处理程序结束;和（b）完全删除group.wait()。

func loadComments(comletion: @escaping ([Episode]) -> Void){ 
    loadEpisodes(completion: { 
     episodes in 
     var fullyEpisodes = [Episode]() 
     let group = DispatchGroup() 
     for episode in episodes { 
      group.enter() 
      WebService().load(resource: episode.comment, comletion: { 
       comments in 
       if let comments = comments { 
        let _episode = Episode(id: episode.id, title: episode.title, comments: comments) 
        fullyEpisodes.append(_episode) 
        print("done") 
       } 
       group.leave() 
      }) 
      // group.leave() 
     } 
     //group.wait() 
     group.notify(queue: .main, execute: { 
      comletion(fullyEpisodes) 
     }) 

    }) 
}

或当清洗了一下尾随的闭包语法和固定completion拼写：

func loadComments(completion: @escaping ([Episode]) -> Void) { 
    loadEpisodes { episodes in 
     var fullyEpisodes = [Episode]() 
     let group = DispatchGroup() 
     for episode in episodes { 
      group.enter() 
      WebService().load(resource: episode.comment) { comments in 
       if let comments = comments { 
        let _episode = Episode(id: episode.id, title: episode.title, comments: comments) 
        fullyEpisodes.append(_episode) 
       } 
       group.leave() 
      } 
     } 
     group.notify(queue: .main) { 
      completion(fullyEpisodes) 
     } 
    } 
}

来源

2016-12-02 14:52:37 Rob

我用你的指令编辑。但是我执行了group.notify ..（comletion（fullyEpisodes））之前执行Webservice（）。load。 @罗布 –

好的。它的工作。非常感谢：） –

同步嵌套的异步任务

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