Alamofire完成工作后如何加载视图？

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• 我的问题：

我正在尝试通过 Alamofire ，然后SubViewController加载其视图。编写代码后，我无法解决Alamofire的异步功能的问题。在Alamofire完成工作之前，始终将视图加载到SubViewController中。

I am trying to load data from Server, through Alamofire, before SubViewController Load its view. After writing the code, I failed to solve the problem of Async Feature of Alamofire. The view is always be loaded in the SubViewController before Alamofire finished its job.

• 部分代码：

ParentViewController：

ParentViewController:

通过 PrepareForSegue（）进入SubViewController。

Leading the way to SubViewController through PrepareForSegue().

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) { if segue.identifier == "CellDetailSegue" { if let indexPaths = self.dateCollectionView.indexPathsForSelectedItems() { let subViewController = segue.destinationViewController as! SubViewConroller } }

SubViewController：

SubViewController:

测试数据是否已由 print（）在其 viewDidLoad（）中加载并在 viewWillAppear（）

Test whether the data has been loaded by print() in the its viewDidLoad() and load the data by dataRequest() in viewWillAppear()

class SubViewController: UIViewController, UITableViewDelegate, UITableViewDataSource { var availablePeriods401 = [String]() var availablePeriods403 = [String]() var availablePeriods405 = [String]() override func viewDidLoad() { super.viewDidLoad() self.dataRequest(self.availablePeriods401) self.dataRequest(self.availablePeriods403) self.dataRequest(self.availablePeriods405) print(self.availablePeriods401.count) print(self.availablePeriods403.count) print(self.availablePeriods405.count) } func dataRequest(_ target: [String]) { Alamofire.request(.POST, "httpbin/get", parameters: ["foo": "bar"]).responseJSON { . . . target = Result } } }

• 问题描述：

不能为SubViewController中的三个变量分配有效值视图加载后。

Three variables in the SubViewController can not be assigned the valid values after view was loaded.

三个输出的结果全部为0。

Three Outputs' results are all 0.

但是如果设置<$ c，我可以获得有效计数 dataRequest（）中的$ c> print（）。

But I can get valid count if I set print() in the dataRequest().

• 我的问题：

如何确保 Alamofire 完成

我应该在哪里放置Alamofire请求功能？ viewWillApper（）？ viewDidApper（）？

Where Shall I put the Alamofire Request Function? viewWillApper()? viewDidApper()?

我什至应该在ParentViewController的 PrepareForSegue（）中完成请求工作吗？ / code>？

Should I even finished requesting job in ParentViewController's PrepareForSegue() ?

请教我如何解决此问题。

Please teach me how to solve this problem.

非常感谢您的指导和时间。

A big appreciation for your guide and time.

Ethan Joe

Ethan Joe

推荐答案

我注意到的第一件事是您正在执行3个异步请求，而不是一个。您可以使用完成处理程序，但是哪个？我认为您有2个选择。

The first thing I noticed is that you are doing 3 asynchronous requests, not one. You could use a completion handler but which one? I think you have 2 options.

• 嵌套网络通话，以便完成一个开始下一个。这种方法的缺点是它们将按顺序运行，如果添加更多，则必须继续嵌套。如果您仅进行2次调用，则这样的方法可能会行，但除此之外，它将变得越来越困难。
• 使用信号量等待直到从所有加载所有数据为止。远程通话。使用完成处理程序来发信号量。如果要使用此方法，则必须在后台线程上完成，因为使用信号量会阻塞该线程，并且您不希望在主线程上发生这种情况。

这三个呼叫将同时发生。即使AlamoFire尚未完成，该函数也会返回。

These three calls will all happen simultaneously. And the functions will return even though AlamoFire has not completed.

self.dataRequest(self.availablePeriods401) self.dataRequest(self.availablePeriods403) self.dataRequest(self.availablePeriods405)

这些将执行，无论AlamoFire是否已完成。

These will execute, whether AlamoFire has completed or not.

print(self.availablePeriods401.count) print(self.availablePeriods403.count) print(self.availablePeriods405.count)

使用信号量看起来像这样：

Using semaphores would look something like this:

override func viewWillAppear(animated: Bool) { // maybe show a "Please Wait" dialog? loadMyData() { (success) in // hide the "Please Wait" dialog. // populate data on screen } } func loadMyData(completion: MyCompletionHandler) { // Do this in an operation queue so that we are not // blocking the main thread. let queue = NSOperationQueue() queue.addOperationWithBlock { let semaphore = dispatch_semaphore_create(0) Alamofire.request(.POST, "httpbin/get", parameters: ["foo": "bar1"]).responseJSON { // This block fires after the results come back // do something dispatch_semaphore_signal(semaphore); } Alamofire.request(.POST, "httpbin/get", parameters: ["foo": "bar2"]).responseJSON { // This block fires after the results come back // do something dispatch_semaphore_signal(semaphore); } Alamofire.request(.POST, "httpbin/get", parameters: ["foo": "bar3"]).responseJSON { // This block fires after the results come back // do something dispatch_semaphore_signal(semaphore); } dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER) dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER) dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER) completion(true) } }

Apple Docs-Grand Central Dispatch

如何使用信号量

我要为您解决的问题是，如果不是所有的网络电话都失败了，您将怎么办？

The question I have for you is what are you going to do if some, bit not all of the web calls fail?