ios - GCD : Making Sequential Download Calls; ONE BY ONE

Question

场景

该应用程序会逐个下载用户订阅。此调用将在多个位置进行(在另一个网络调用之后的完成 block 中以及从 UIAlertController 按下按钮)。逻辑是下载所有订阅，一旦一个订阅下载失败，它就会转到下一个，直到所有订阅都下载完毕，然后我们的 SVProgressHUD 关闭。当我们从 Xcode 构建和运行代码时，代码运行良好。但是当我们构建 IPA 并发送给我们的客户时，此逻辑会造成某种停顿，并且 SVProgressHUD 警报会一直旋转:

这是一个大问题，因为我们的应用程序专注于从订阅中下载内容。

为什么这个逻辑在我存档并从中构建 IPA 后停止，但在我从 Xcode 构建和运行时没有？

代码如下:

// Making the call 

    DispatchQueue.main.async {
        DGWebService().syncUserSubscribedContent {
            DispatchQueue.main.async {
                self.finishLogin()
            }
        }
    }

---

// Sequentially going through each subscription and downloading them

    func syncUserSubscribedContent(completion: @escaping Constants.WebService.ContentCompletion) {
        let subscriptions = MPTUser.sharedUser.getSubscriptionsForDownload()
        DispatchQueue.global().async {
            if subscriptions.count > 0 {
                var index:Int = 0
                var t = subscriptions.count
                var downloading: Bool = false
                while t != 0 {
                    if downloading == false {
                        downloading = true
                        if index < 0 {
                            index = 0
                        }
                        if index > subscriptions.count - 1 {
                            index = subscriptions.count - 1
                        }
                        if index <= subscriptions.count {
                            let subscription = subscriptions[index]
                            if subscription.didDownloadContent == false {
                                if let subscriptionID = subscription.subscriptionID {
                                    DispatchQueue.main.async {
                                        SVProgressHUD.show(withStatus: "Downloading Documents\nfor\n\(subscription.functionalGroupName!)\n\(index+1) of \(subscriptions.count)")
                                    }
                                    self.getUserSubscribedContent(subscriptionID: subscriptionID, completion: { (success) in
                                        subscription.didDownloadContent = true
                                        index += 1
                                        t -= 1
                                        downloading = false
                                    })
                                }
                                else {
                                    index += 1
                                    t -= 1
                                    downloading = false
                                }
                            }
                        }
                        else {
                            index += 1
                            t -= 1
                            downloading = false
                        }
                    }
                }
            }
            completion()
        }
    }

---

self.getUserSubscribedContent 是一个下载内容并在 block 中发送完成的函数。

如果有人可以帮助我，我将不胜感激。

Answer 1

您可以尝试使用 DispatchGroup。这是一个粗略的(未经测试的)示例:

DispatchQueue.global().async {
    let subscriptions = MPTUser.sharedUser.getSubscriptionsForDownload()
    let group = DispatchGroup()
    var completed = 0
    let completion: (Bool) -> Void = {
        if $0 {
            completed += 1
        }
        group.leave()
        DispatchQueue.main.async {
            SVProgressHUD.show(withStatus: "Downloading Documents\nfor\n\(subscription.functionalGroupName!)\n\(completed) of \(subscriptions.count)")
        }
    }
    for subscription in subscriptions {
        self.getUserSubscribedContent(subscriptionID: subscription.subscriptionID, completion: completion)
        group.enter()
    }
    // However long you want to wait (in seconds) before timing out
    _ = group.wait(timeout: .now() + 30)
}