URLSession.shared.dataTaskPublisher在IOS 13.3上不起作用 [英] URLSession.shared.dataTaskPublisher not working on IOS 13.3

问题描述

尝试发出网络请求时，出现错误

When trying to make a network request, I'm getting an error

finished with error [-999] Error Domain=NSURLErrorDomain Code=-999 "cancelled"

如果我使用 URLSession.shared.dataTask 而不是 URLSession.shared.dataTaskPublisher ，它将在IOS 13.3上运行.

If I use URLSession.shared.dataTask instead of URLSession.shared.dataTaskPublisher it will work on IOS 13.3.

这是我的代码:

return  URLSession.shared.dataTaskPublisher(for : request).map{ a in
    return a.data
}
.decode(type: MyResponse.self, decoder: JSONDecoder())
.receive(on: DispatchQueue.main)
.eraseToAnyPublisher()

此代码适用于IOS 13.2.3.

This code worked on IOS 13.2.3.

推荐答案

您没有显示足够的代码，但是根据症状，您可以清楚地知道问题所在:发布者/订阅者对象的生存时间不够长.我敢说您的代码总是错误的，这似乎是成功的怪癖.确保您的发布者(尤其是您的订阅者)保留在长期存在的对象(例如实例属性)中，以便有时间进行网络通信.

You have not shown enough code, but based on the symptom it is clear what the problem is: your publisher / subscriber objects are not living long enough. I would venture to say that your code was always wrong and it was just a quirk that it seemed to succeed. Make sure that your publisher and especially your subscriber are retained in long-lived objects, such as instance properties, so that the network communication has time to take place.

这是一个如何使用数据任务发布者的可行示例:

Here's a working example of how to use a data task publisher:

class ViewController: UIViewController {
    let url = URL(string:"https://apeth.com/pep/manny.jpg")!
    lazy var pub = URLSession.shared.dataTaskPublisher(for: url)
        .compactMap {UIImage(data: $0.data)}
        .receive(on: DispatchQueue.main)
    var sub : AnyCancellable?
    override func viewDidLoad() {
        super.viewDidLoad()
        let sub = pub.sink(receiveCompletion: {_ in}, receiveValue: {print($0)})
        self.sub = sub
    }
}

这会打印< UIImage:0x6000008ba490匿名{180，206}> ，这是正确的(如您自己转到该URL所见).

That prints <UIImage:0x6000008ba490 anonymous {180, 206}>, which is correct (as you can see by going to that URL yourself).

我要说的是，如果您不说 self.sub = sub ，您将得到报告的错误:订阅者 sub ，仅仅是本地的，它会立即不复存在，并且网络交易会被过早取消(由于您报告了错误).

The point I'm making is that if you don't say self.sub = sub, you get exactly the error you are reporting: the subscriber sub, which is merely a local, goes out of existence immediately and the network transaction is prematurely cancelled (with the error you reported).

编辑我认为代码是在 .store(in:)方法存在之前编写的；如果我今天写的话，我会用它代替 sub 属性.但是原理是一样的.

EDIT I think that code was written before the .store(in:) method existed; if I were writing it today, I'd use that instead of a sub property. But the principle is the same.

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