ios – 如何解决Swift 4中的内存循环URLSession.downloadTask？

@L_262_0@一个基本的viewController,只有一个按钮,当点击时,调用一个方法开始从给定的有效URL下载图像.

我非常小心地将任何强大的指针传递给viewcontroller.而且我可以将视图控制器解散掉并且回到演示控制器而没有任何问题.但是,即使调用了viewcontroller的deinit,也不会释放由viewcontroller创建的Web()对象实例.

我究竟做错了什么？

BTW：启动文件下载,报告进度并报告文件位置.但是,一旦文件下载完毕,该对象永远不会被释放.

viewController.swift

@IBACtion func buttonTapped(_ sender: UIButton) {
   //first create an instance of Web class (download Helper)
   let web = Web(url: "https://www.google.com.sa/images/branding/googlelogo/2x/googlelogo_color_120x44dp.png")

   // all call BACk closures have no reference to self    
   web.downloadFile(
       finishedHandler: {fileLOCATIOn in print("file stored to \(fileLOCATIOn)")},progressHandler: {Bytes,@R_21_10586@l in print("written \(bytes) out of \(@R_21_10586@l)")},errorHandler: {msg in print("error: \(msg)")}
  )

}

我已经将Web()定义为NSObject,它符合URLSessionDownloadDelegate以利用委托事件方法(didFinishDownload / didWriteBytes等).

Web.swift

import UIKit

class Web : NSObject {
    var urlToDownload : String?

   // the following variables are references to closures passed to the object.
    var progressCallBACk : ((_ bytesWritten:Int64,_ @R_21_10586@lExpectedBytes: Int64)->())?
    var finishedCallBACk : ((_ fileLOCATIOn: String)->())?


    static var instanceCount = 0 // keep track of number of instances created

    init(url: String) {

       Web.instanceCount += 1
       urlToDownload = url
       print(" new instance of Web created. @R_21_10586@l : \(Web.instanceCount)")
   }

   deinit {
      Web.instanceCount -= 1
      print("Web instance deallocated. Remaining: \(Web.instanceCount)")

   }
}

我将文件下载逻辑添加为同一文件的扩展名：

extension Web : URLSessionDownloadDelegate {

    func downloadFile(
        finishedHandler: @escaping (_ fileLOCATIOn:string)->(),progressHandler: @escaping (_ bytesWritten:Int64,_ @R_21_10586@lBytes: Int64)->(),errorHandler: @escaping (_ errorMsg:string)->()) {

        // we need to capture the closure because,these will
        // be called once the delegate methods are triggered
        self.progressCallBACk = progressHandler
        self.finishedCallBACk = finishedHandler


        if let url = URL(String: self.urlToDownload!) {
             let session = URLSession(
                configuration: .default,delegate: self,delegateQueue: nil)

            let task = session.downloadTask(with: url)

            task.resume()

        }

    }

    // MARK :- Delegate methods
    func urlSession(_ session: URLSession,downloadTask: URLSessionDownloadTask,didFinishDownloadingTo LOCATIOn: URL) {
        // call the closure if it still exists
        self.finishedCallBACk?(LOCATIOn.absoluteString)
    }

    func urlSession(_ session: URLSession,didWriteData bytesWritten: Int64,@R_21_10586@lBytesWritten: Int64,@R_21_10586@lBytesExpectedToWrite: Int64) {
        // report progress by calling captured closure,if exists
        self.progressCallBACk?(@R_21_10586@lBytesWritten,@R_21_10586@lBytesExpectedToWritE)
    }
}

if let url = URL(String: self.urlToDownload!) {
     let session = URLSession(
        configuration: .default,delegateQueue: nil)

    let task = session.downloadTask(with: url)

    task.resume()
}

if let url = URL(String: self.urlToDownload!) {
    let session = URLSession(
        configuration: .default,delegateQueue: nil)

    let task = session.downloadTask(with: url)

    task.resume()
    // here we go:
    session.finishTasksAndInvalidate()
}