Question

我在执行https请求时遇到问题，如果请求没有任何错误我从未收到消息，这是一个命令行工具应用程序，我有一个允许http请求的plist，我总是看到完成块。

typealias escHandler = ( URLResponse?, Data? ) -> Void

func getRequest(url : URL, _ handler : @escaping escHandler){    
let session = URLSession.shared
var request = URLRequest(url:url)
request.cachePolicy = .reloadIgnoringLocalCacheData
request.httpMethod = "GET"
let task = session.dataTask(with: url ){ (data,response,error) in
        handler(response,data)
}

task.resume()
}


func startOp(action : @escaping () -> Void) -> BlockOperation{

let exOp = BlockOperation(block: action)    
exOp.completionBlock = {

print("Finished")

}
return exOp
}

     for sUrl in textFile.components(separatedBy: "\n"){
     let url = URL(string: sUrl)!

        let queu = startOp {
            getRequest(url: url){  response, data  in

                print("REACHED")



            }

        }
      operationQueue.addOperation(queu)
      operationQueue.waitUntilAllOperationsAreFinished()

Answer 1

一个问题是您的操作仅仅是启动请求，但由于请求是异步执行的，因此操作会立即完成，而不是实际等待请求完成。在异步请求完成之前，您不想完成操作。

如果要对操作队列执行此操作，诀窍是您必须继承NSOperation，从true返回isAsynchronous。然后，当您开始请求时更改isExecuting，并在完成请求时更改isFinished，为这两者执行必要的KVO。这一点在Concurrency Programming Guide: Defining a Custom Operation Object中概述，特别是在Configuring Operations for Concurrent Execution部分。（注意，本指南有点过时（它指的是isConcurrent属性，已被替换为isAsynchronous;它专注于Objective-C;等等），但它引入了你这些问题。

无论如何，这是一个抽象类，我用它来封装所有这些异步操作的愚蠢：

//  AsynchronousOperation.swift

import Foundation

/// Asynchronous Operation base class
///
/// This class performs all of the necessary KVN of `isFinished` and
/// `isExecuting` for a concurrent `NSOperation` subclass. So, to developer
/// a concurrent NSOperation subclass, you instead subclass this class which:
///
/// - must override `main()` with the tasks that initiate the asynchronous task;
///
/// - must call `completeOperation()` function when the asynchronous task is done;
///
/// - optionally, periodically check `self.cancelled` status, performing any clean-up
///   necessary and then ensuring that `completeOperation()` is called; or
///   override `cancel` method, calling `super.cancel()` and then cleaning-up
///   and ensuring `completeOperation()` is called.

public class AsynchronousOperation : Operation {

    override public var isAsynchronous: Bool { return true }

    private let stateLock = NSLock()

    private var _executing: Bool = false
    override private(set) public var isExecuting: Bool {
        get {
            return stateLock.withCriticalScope { _executing }
        }
        set {
            willChangeValue(forKey: "isExecuting")
            stateLock.withCriticalScope { _executing = newValue }
            didChangeValue(forKey: "isExecuting")
        }
    }

    private var _finished: Bool = false
    override private(set) public var isFinished: Bool {
        get {
            return stateLock.withCriticalScope { _finished }
        }
        set {
            willChangeValue(forKey: "isFinished")
            stateLock.withCriticalScope { _finished = newValue }
            didChangeValue(forKey: "isFinished")
        }
    }

    /// Complete the operation
    ///
    /// This will result in the appropriate KVN of isFinished and isExecuting

    public func completeOperation() {
        if isExecuting {
            isExecuting = false
        }

        if !isFinished {
            isFinished = true
        }
    }

    override public func start() {
        if isCancelled {
            isFinished = true
            return
        }

        isExecuting = true

        main()
    }
}

我将此Apple扩展程序用于NSLock以确保我同步上述状态更改：

extension NSLock {

    /// Perform closure within lock.
    ///
    /// An extension to `NSLock` to simplify executing critical code.
    ///
    /// - parameter block: The closure to be performed.

    func withCriticalScope<T>(block: () -> T) -> T {
        lock()
        let value = block()
        unlock()
        return value
    }
}

然后，我可以创建一个使用它的NetworkOperation：

class NetworkOperation: AsynchronousOperation {

    let url: URL
    let session: URLSession
    let requestCompletionHandler: (Data?, URLResponse?, Error?) -> ()

    init(session: URLSession, url: URL, requestCompletionHandler: @escaping (Data?, URLResponse?, Error?) -> ()) {
        self.session = session
        self.url = url
        self.requestCompletionHandler = requestCompletionHandler

        super.init()
    }

    private weak var task: URLSessionTask?

    override func main() {
        let task = session.dataTask(with: url) { data, response, error in
            self.requestCompletionHandler(data, response, error)
            self.completeOperation()
        }
        task.resume()
        self.task = task
    }

    override func cancel() {
        task?.cancel()
        super.cancel()
    }

}

无论如何，完成此操作后，我现在可以为网络请求创建操作，例如：

let queue = OperationQueue()
queue.name = "com.domain.app.network"

let url = URL(string: "http://...")!
let operation = NetworkOperation(session: URLSession.shared, url: url) { data, response, error in
    guard let data = data, error == nil else {
        print("\(error)")
        return
    }

    let string = String(data: data, encoding: .utf8)
    print("\(string)")
    // do something with `data` here
}

let operation2 = BlockOperation {
    print("done")
}

operation2.addDependency(operation)

queue.addOperations([operation, operation2], waitUntilFinished: false) // if you're using command line app, you'd might use `true` for `waitUntilFinished`, but with standard Cocoa apps, you generally would not

注意，在上面的例子中，我添加了第二个操作，只是打印了一些东西，使其依赖于第一个操作，以说明第一个操作没有完成，直到网络请求完成。

显然，在我的示例中，您通常不会使用原始示例的waitUntilAllOperationsAreFinished，也不会使用waitUntilFinished的{{1}}选项。但是因为你正在处理一个你不想在这些请求完成之前退出的命令行应用程序，所以这种模式是可以接受的。（我只是为了未来的读者而提到这一点，他们对addOperations的自由使用感到惊讶，这通常是不可取的。）

如何在Swift 3中同时进行https请求

1 个答案: