Question

我的代码执行请求链接，如 A-＆gt; B-＆gt; C ，我正在使用URLSession所有请求都按正确的顺序完成并具有预期的行为。但我想知道如何优化这种链接，因为它看起来非常复杂而且不可重复使用。我正在寻找如何以更灵活的方式进行链接的建议。

我的代码：

URLSession.shared.dataTask(with: URLRequest(url: URL(string: "first")!)){ data , res , err in
    let second = URLRequest(url: URL(string: "second")!)
    URLSession.shared.dataTask(with: second){ data , res , err in
        let third = URLRequest(url: URL(string: "second")!)
        URLSession.shared.dataTask(with:third){ data , res , err in
         }.resume()
    }.resume()
}.resume()

Answer 1

实际上，您可以使用如下所示的OperationQueues来使用依赖项：

$(document).ready(function(){
    var imageList = ['https://www.w3schools.com/css/paris.jpg', 'https://www.w3schools.com/css/trolltunga.jpg', 'https://www.w3schools.com/css/rock600x400.jpg', 'https://www.w3schools.com/css/lights600x400.jpg', 'https://www.w3schools.com/css/img_forest.jpg', 'https://www.w3schools.com/css/pineapple.jpg'];
    $('img').attr('src',imageList[0]);
    $("button").click(function(){
      var buttonId = $(this).attr('id').split('-');
      
      $('img').attr('src',imageList[buttonId[1]]);
    });
});

Answer 2

正如@ Paulw11所说：

PromiseKit + PMKFoundation

import PromiseKit
import PMKFoundation

let session = URLSession.shared
firstly {
    session.dataTask(with: URLRequest(url: URL(string: "first")!))
} .then { data in
    session.dataTask(with: URLRequest(url: URL(string: "second")!))
} .then { data in
    session.dataTask(with: URLRequest(url: URL(string: "third")!))
} .then { data -> () in
    // The data here is the data fro the third URL
} .catch { error in
    // Any error in any step can be handled here
}

重试1次（且仅1次），您可以使用recover。 recover与catch类似，但预计可以重试之前的then。但是，这不是一个循环，只执行一次。

func retry(url: URL, on error: Error) -> Promise<Data> {
    guard error == MyError.retryError else { throw error }

    // Retry the task if a retry-able error occurred.
    return session.dataTask(with: URLRequest(url: url))
}

let url1 = URL(string: "first")!
let url2 = URL(string: "second")!
let url3 = URL(string: "third")!

let session = URLSession.shared
firstly {
    session.dataTask(with: URLRequest(url: url1))
} .then { data in
    session.dataTask(with: URLRequest(url: url2))
} .recover { error in
    retry(url: url2, on: error)
} .then { data in
    session.dataTask(with: URLRequest(url: url3))
} .recover { error in
    retry(url: url3, on: error)
} .then { data -> () in
    // The data here is the data fro the third URL
} .catch { error in
    // Any error in any step can be handled here
}

注意：要在不指定返回类型且需要return语句的情况下完成此工作，我需要then和recover完全为1行。所以我创建了进行处理的方法。

如何在Swift中优化链接异步请求

2 个答案: