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Question

我对Swift和iOS开发相当新，所以请原谅使用的所有/所有语句和术语......

我正在创建一个新的Downloader对象（只是为了下载PDF文件），我需要在我的ViewController中调用一个方法，该方法显示文件已成功下载的消息。除非我做了一些非常愚蠢的事情，似乎无法让它发挥作用。

我正在使用AhmetAkkök在this question上的答案，当我尝试使用yourOwnObject.showDownloadCompleted（）时，它无法找到该方法。

任何和所有帮助将不胜感激！

ViewController中的代码：

override func viewDidLoad(){

    super.viewDidLoad();
    let pdfURL = "exampleToPFD.com/mypdf.pdf";

    let url = NSURL(string: pdfURL);

    let d = Downloader(yourOwnObject: self);
    d.download(url!);

}

func showDownloadComplete(){
    print("done");
}

Downloader.swift中的代码：

import Foundation

class Downloader : NSObject, NSURLSessionDownloadDelegate{
var url : NSURL?

// will be used to do whatever is needed once download is complete
var yourOwnObject : NSObject?
var downloaded = false;
var documentDestination = "";

init(yourOwnObject : NSObject){
    self.yourOwnObject = yourOwnObject
}


//is called once the download is complete
func URLSession(session: NSURLSession, downloadTask: NSURLSessionDownloadTask, didFinishDownloadingToURL location: NSURL){
    //copy downloaded data to your documents directory with same names as source file
    let documentsUrl =  NSFileManager.defaultManager().URLsForDirectory(.DocumentDirectory, inDomains: .UserDomainMask).first
    let destinationUrl = documentsUrl!.URLByAppendingPathComponent(url!.lastPathComponent!)
    let dataFromURL = NSData(contentsOfURL: location)
    dataFromURL!.writeToURL(destinationUrl, atomically: true)

    //now it is time to do what is needed to be done after the download

    print("download done...");
    // call to the parent method here

    documentDestination = destinationUrl.absoluteString;
    print("DestURL" + (destinationUrl.absoluteString));
}

//method to be called to download
func download(url: NSURL){

    self.url = url

    //download identifier can be customized. I used the "ulr.absoluteString"
    let sessionConfig = NSURLSessionConfiguration.backgroundSessionConfigurationWithIdentifier(url.absoluteString)
    let session = NSURLSession(configuration: sessionConfig, delegate: self, delegateQueue: nil)
    let task = session.downloadTaskWithURL(url);

    task.resume();
}
}

Answer 1

您可以使用委托来实现这一目标。您可以尝试以下

Downloader.swift

import Foundation

protocol DownloadDelegate {
    func downloadCompleted()
}

class Downloader : NSObject, NSURLSessionDownloadDelegate{
var url : NSURL?
var downloadDelegate : DownloadDelegate!
// will be used to do whatever is needed once download is complete
var downloaded = false;
var documentDestination = "";

//is called once the download is complete
func URLSession(session: NSURLSession, downloadTask: NSURLSessionDownloadTask, didFinishDownloadingToURL location: NSURL){
    //copy downloaded data to your documents directory with same names as source file
    let documentsUrl =  NSFileManager.defaultManager().URLsForDirectory(.DocumentDirectory, inDomains: .UserDomainMask).first
    let destinationUrl = documentsUrl!.URLByAppendingPathComponent(url!.lastPathComponent!)
    let dataFromURL = NSData(contentsOfURL: location)
    dataFromURL!.writeToURL(destinationUrl, atomically: true)

    //now it is time to do what is needed to be done after the download

    print("download done...");
    downloadDelegate. downloadCompleted()

    documentDestination = destinationUrl.absoluteString;
    print("DestURL" + (destinationUrl.absoluteString));
}

//this is to track progress
func URLSession(session: NSURLSession, downloadTask: NSURLSessionDownloadTask, didWriteData bytesWritten: Int64, totalBytesWritten: Int64, totalBytesExpectedToWrite: Int64){
    print((String)(totalBytesWritten)+"/"+(String)(totalBytesExpectedToWrite));

}

// if there is an error during download this will be called
func URLSession(session: NSURLSession, task: NSURLSessionTask, didCompleteWithError error: NSError?){

    if(error != nil){

        //handle the error
        print("Download completed with error: \(error!.localizedDescription)");

    }

}


//method to be called to download
func download(url: NSURL){

    self.url = url

    //download identifier can be customized. I used the "ulr.absoluteString"
    let sessionConfig = NSURLSessionConfiguration.backgroundSessionConfigurationWithIdentifier(url.absoluteString)
    let session = NSURLSession(configuration: sessionConfig, delegate: self, delegateQueue: nil)
    let task = session.downloadTaskWithURL(url);

    task.resume();
}
}

ViewController：

class ViewController: UIViewController,DownloadDelegate{
    override func viewDidLoad(){

        super.viewDidLoad();
        // Do any additional setup after loading the view, typically from a nib.
        let pdfURL = "exampleToPFD.com/mypdf.pdf";

        let url = NSURL(string: pdfURL);

        let d = Downloader();
        d.downloadDelegate = self
        d.download(url!);


        showToast("Download Started...");

    }

    func downloadCompleted() {
       //download completed
    }
}