ios - 数组回调

Question

我正在尝试设置以下方法，以便在执行完所有 show.getVideosForShow() 成功 block 并附加所有视频后执行成功 block 。注意:show.getVideosForShow() 是异步的，可能需要几秒钟才能得到结果。有人可以提供一些帮助吗？

private func getNextVideoRecommendations(success: ([Video]) -> ()) {
    var relatedVideos = [Video]()
    if let relatedShows = self.videoCurrentlyPlaying?.show?.getShowsWithSameGenre(fetchLimit: 3) {
        for show in relatedShows {
            show.getVideosForShow(tvSeason: nil, longForm: true, sortType: VideoSort.Latest, success: { (videos: [Video]) in
                print("Found Related Show: \(show.title)")
                if videos.count > 0 {
                    relatedVideos.append(videos[0])
                }
            })
        }
        print("Finished all operations")
        success(relatedVideos)
    }
}

Answer 1

这是 dispatch groups 的一个很好的用例，这允许您在所有操作完成后提交另一个 block :

private func getNextVideoRecommendations(success: ([Video]) -> ()) {
    var relatedVideos = [Video]()
    if let relatedShows = self.videoCurrentlyPlaying?.show?.getShowsWithSameGenre(fetchLimit: 3) {
        <b>let group = dispatch_group_create()</b>
        for show in relatedShows {
            <b>dispatch_group_enter(group)</b>  // start tracking one unit of work
            show.getVideosForShow(tvSeason: nil, longForm: true, sortType: VideoSort.Latest, success: { (videos: [Video]) in
                print("Found Related Show: \(show.title)")
                if videos.count > 0 {
                    relatedVideos.append(videos[0])
                }
                <b>dispatch_group_leave(group)</b>  // finish one unit of work
            })
        }
        <b>dispatch_group_notify(group, dispatch_get_main_queue())</b> {  // and when done...
            print("Finished all operations")
            success(relatedVideos)
        }
    }
}