关于ios：如何运行多个NSURLSessionDownloadTask \\，以便我可以从Instagram下载多个用户照片流？


How to run multiple NSURLSessionDownloadTask's so I can download multiple user photo streams from Instagram?

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//
//  ViewController.swift
//  Fashun
//
//  Created by Alex Macleod on 20/10/14.
//  Copyright (c) 2014 Alex Macleod. All rights reserved.
//

import UIKit

class ViewController: UIViewController, UICollectionViewDelegateFlowLayout, UICollectionViewDataSource {

var collectionView: UICollectionView?

var instanceOfCustomObject: CustomObject = CustomObject()
var accessToken: NSString!
var userDefaults: NSUserDefaults!
let colorWheel = ColorWheel()
var photoCount: Int! = 0
let photos = NSMutableArray()

override func viewDidLoad() {
    super.viewDidLoad()

    userDefaults = NSUserDefaults.standardUserDefaults()
    self.accessToken = userDefaults!.objectForKey("accessToken") as NSString
    println(self.accessToken)

//        instanceOfCustomObject.someProperty ="Hello World"
//        var accessToken : NSString? = NSString(instanceOfCustomObject.accessToken)
//        println(accessToken)
//        instanceOfCustomObject.authorize()

// Do any additional setup after loading the view, typically from a nib.
    let layout: UICollectionViewFlowLayout = UICollectionViewFlowLayout()
//        layout.sectionInset = UIEdgeInsets(top: 20, left: 0, bottom: 0, right: 0)
    layout.itemSize = CGSize(width: 124, height: 124)
    layout.minimumInteritemSpacing = 1.0
    layout.minimumLineSpacing = 1.0
    collectionView = UICollectionView(frame: self.view.frame, collectionViewLayout: layout)
    collectionView!.dataSource = self
    collectionView!.delegate = self
    collectionView!.registerClass(Cell.self, forCellWithReuseIdentifier:"Cell")
    collectionView!.backgroundColor = UIColor.whiteColor()
    self.view.addSubview(collectionView!)

    getData()
}

    func getData() -> Void {
        let baseUrl = NSURL(string:"https://api.instagram.com/v1/users/7522782/media/recent/?access_token=\\(self.accessToken)")

//        let forcastUrl = NSURL(string:"37.8267,-122.423", relativeToURL: baseUrl)

        //        let data = NSData(contentsOfURL: forcastUrl)
        //        println(data)
        let sharedSession = NSURLSession.sharedSession()
        let downloadTask: NSURLSessionDownloadTask = sharedSession.downloadTaskWithURL(baseUrl!, completionHandler: { (location: NSURL!, response: NSURLResponse!, error: NSError!) -> Void in


            //            var urlContents = NSString.stringWithContentsOfURL(location, encoding: NSUTF8StringEncoding, error: nil)
            //            println(urlContents)

            let dataObject = NSData(contentsOfURL: baseUrl!)

            if (error == nil) {
                let responseDictionary: NSDictionary = NSJSONSerialization.JSONObjectWithData(dataObject!, options: nil, error: nil) as NSDictionary
//                println(responseDictionary)

                var currentResponse = responseDictionary.valueForKeyPath("data.images.standard_resolution.url") as NSArray



                dispatch_async(dispatch_get_main_queue(), { () -> Void in

//                    for url in currentResponse {
//                        var urlStrings: NSString = url as NSString
//                        
//                        var images =  UIImage(data: NSData(contentsOfURL: NSURL(string:urlStrings)!)!)
//
//                    }
                    for url in currentResponse {
                        var urls: NSString = url as NSString
                        //                        println(images)
                        var photoUrls = NSURL(string: urls)

                        var err: NSError?
                        var imageData :NSData = NSData(contentsOfURL: photoUrls!,options: NSDataReadingOptions.DataReadingMappedIfSafe, error: &err)!
                        self.photos.addObject(UIImage(data:imageData)!)
                        println(self.photos)
                    }

                    self.photoCount = currentResponse.count as Int

                    self.collectionView?.reloadData()

                })

            } else {

                let networkIssueController = UIAlertController(title:"Error", message:"Something went wrong get a better phone you pleb!", preferredStyle: .ActionSheet)
                let okButton = UIAlertAction(title:"OK", style: .Default, handler: nil)
                networkIssueController.addAction(okButton)
                let cancelButton = UIAlertAction(title:"Cancel", style: .Cancel, handler: nil)
                networkIssueController.addAction(cancelButton)

                self.presentViewController(networkIssueController, animated: true, completion: nil)

                dispatch_async(dispatch_get_main_queue(), { () -> Void in
                    //Stop refresh animation


                })
            }
        })

        downloadTask.resume()

    }


override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}

func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    return photoCount

}

func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
    let cell = collectionView.dequeueReusableCellWithReuseIdentifier("Cell", forIndexPath: indexPath) as Cell
//                println(photos)
//            cell.textLabel.text ="Text"
    cell.imageView.image = photos.objectAtIndex(indexPath.row) as? UIImage
//    cell.photo = self.photos[indexPath.row] as? NSDictionary
    cell.imageView.backgroundColor = colorWheel.randomColor()

    return cell
}
}

您可以看到我有一个NSURLDownload会话，该会话从用户" 7522782"下载instagram信息。我解析数据并计算" currentResponse "数组以获取集合视图中所需的单元格数。然后，我将信息转换网址解析为UIimages并将其放入单元格中。

如何为一个以上的用户执行此操作。我想显示20位用户的照片。
请记住，我需要汇总所有用户的照片总数，以告诉我的收藏夹视图可以制作多少个单元格。

谢谢。

相关讨论

这是我现在想的一种方式...

首先修复您使用分派的方式...关于分派队列的好答案

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//Might run into an issue that if you insert more heavy logic here your UI will get stuck until processing ends.
dispatch_async(dispatch_get_main_queue(), { () -> Void in }

因此，请改为使用dispatch_get_global_queue进行后台线程处理，然后在要运行将在后台闭包(块)内更新UI的代码时调用dispatch_get_main_queue。

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//Correct way to use it to do Background work.
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), {

   //async code the callings to the NSUrlSession any other logic

       dispatch_async(dispatch_get_main_queue(), { () -> Void in
          //Do UI Updates Code.
       }

}

现在根据您的具体情况。您正在正确地处理该用户，获取该用户的"照片"的所有网址，因此现在添加类似这样的内容以处理同一屏幕上的多个用户。问题是下载20张用户照片需要花费很长时间，但是由于您执行的是异步操作，因此屏幕不会卡住。

对照片进行矩阵处理；主阵列中的每个阵列都是每个用户的照片集。

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var photoUserMatrix = [NSMutableArray]() //using Swift array and NSMutableArray

或者使用它，因为您更倾向于NSMutableArrays

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var photoUserMatrix = NSMutableArray()  
photoUserMatrix.addObject(NSMutableArray())//Each Photo Set per user is a new array.

矩阵的问题是发现执行时间为O(N ^ 2)。

现在无论如何您都可以拥有X个用户，并且您的代码可以处理它。通过使用这段代码。

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//Use this pseudo code to start downloading the multiple pictures for the users.
for i in 0...countOfUsers{

   //Create the array of Photos for this user.
   var newPhotoSet = NSMutableArray()

   //Now use your code that downloads the photos with
   //the Urls given for that users photos. with another loop on the Count of Urls/Photos
   for pos in 0...countOfUrls{

         //Download the Image with NSUrlSession

         //and add the photo to the new Array in the CompletionHandler
         newPhotoSet.AddObject(newImageDownloaded);
   }

   photoUserMatrix.addObject(newPhotoSet)


}

显示CollectionViewCells的代码。

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for photoSet in photoUserMatrix as (NSMutableArray) {

    var count:Int = photoSet.count
    for i in 0...count{
        //use algorithm to display downloaded pictures in CollectionView.
        //If any image is nil do not display that image.
       //Same Code can be used to do the sum of all photos in each array.
    }


}

请记住，这不是最佳解决方案。应用程序的设计也无济于事，在同一屏幕上为20个用户加载图像是一个问题，除非图像真的很小，否则您将在那里运行。

我也建议您将此工作逻辑代码添加到方法中，该方法将为需要下载图像的每个用户调用Dispatch_get_global_queue，从而使其更加并行。

PS：如果您遇到任何问题，请告诉我，我们将很乐意为您提供帮助。

相关讨论