アマゾンのAWSのS3に上がっている画像データを読み込み、`ScrollView`に表示するというコードを書きました。

UIの更新は`dispatch_get_main_queue()`の中に明記することを記事で見たので、以下のように記述したのですが、最初の一枚しか`scrollview`に追加されません。デバックをしたところ、`addImage`は画像の枚数回呼び出されているそうです。

複数枚の画像を非同期的に読み込んで、一枚一枚順を追って`scrollview`に追加したいです。複数枚の追加はどうしたらいいでしょうか？

downloadメソッドを追加しました。

```

    class LoadViewController: UIViewController,UIScrollViewDelegate {
        var loadImages:[UIImage] = []
        @IBOutlet weak var scrollView: UIScrollView!
        var uploadRequests = Array<AWSS3TransferManagerUploadRequest?>()
        var uploadFileURLs = Array<NSURL?>()
        var downloadRequests = Array<AWSS3TransferManagerDownloadRequest?>()
        var downloadFileURLs = Array<NSURL?>()
    
        override func viewDidLoad() {
            super.viewDidLoad()
            self.scrollView.delegate = self
    
            do {
                try NSFileManager.defaultManager().createDirectoryAtURL(
                    NSURL(fileURLWithPath: NSTemporaryDirectory()).URLByAppendingPathComponent("download"),
                    withIntermediateDirectories: true,
                    attributes: nil)
            } catch let error1 as NSError {
                error.memory = error1
                print("Creating 'download' directory failed. Error: \(error)")
            }
    
            listObjects()
        }
        func addImage(image:UIImage)
        {
            let sheight = self.scrollView.frame.height
            let swidth = self.scrollView.frame.width
    
            loadImages.append(image)
            let myImageView = UIImageView()
            myImageView.frame = CGRectMake(swidth * CGFloat(loadImages.count-1), 0, swidth, sheight)
            myImageView.image = image
            scrollView.addSubview(myImageView)
            scrollView.contentSize = CGSizeMake(swidth * CGFloat(loadImages.count), sheight)
    
        }
        func listObjects() {
            let s3 = AWSS3.defaultS3()
    
            let listObjectsRequest = AWSS3ListObjectsRequest()
            listObjectsRequest.bucket = S3BucketName
            s3.listObjects(listObjectsRequest).continueWithBlock { (task) -> AnyObject! in
                if let error = task.error {
                    print("listObjects failed: [\(error)]")
                }
                if let exception = task.exception {
                    print("listObjects failed: [\(exception)]")
                }
                if let listObjectsOutput = task.result as? AWSS3ListObjectsOutput {
                    if let contents = listObjectsOutput.contents as [AWSS3Object]? {
                        for s3Object in contents {
                            let downloadingFileURL = NSURL(fileURLWithPath: NSTemporaryDirectory()).URLByAppendingPathComponent("download").URLByAppendingPathComponent(s3Object.key!)
                            let downloadingFilePath = downloadingFileURL.path!
    
                            if NSFileManager.defaultManager().fileExistsAtPath(downloadingFilePath) {
                                self.downloadRequests.append(nil)
                                self.downloadFileURLs.append(downloadingFileURL)
    
    
                            } else {
                                let downloadRequest = AWSS3TransferManagerDownloadRequest()
                                downloadRequest.bucket = S3BucketName
                                downloadRequest.key = s3Object.key
                                downloadRequest.downloadingFileURL = downloadingFileURL
    
                                self.downloadRequests.append(downloadRequest)
                                self.downloadFileURLs.append(nil)
    
                            }
                            dispatch_async(dispatch_get_main_queue(), { () -> Void in
                                if let data = NSData(contentsOfURL: downloadingFileURL) {
                                    self.addImage(UIImage(data: data)!)
                                    self.displayNum++
                                }
                            })
    
                        }
    
                    }
                }
                return nil
            }
        }
        func download(downloadRequest: AWSS3TransferManagerDownloadRequest) {
            switch (downloadRequest.state) {
            case .NotStarted, .Paused:
                let transferManager = AWSS3TransferManager.defaultS3TransferManager()
                transferManager.download(downloadRequest).continueWithBlock({ (task) -> AnyObject! in
                    if let error = task.error {
                        if error.domain == AWSS3TransferManagerErrorDomain as String
                            && AWSS3TransferManagerErrorType(rawValue: error.code) == AWSS3TransferManagerErrorType.Paused {
                                print("Download paused.")
                        } else {
                            print("download failed: [\(error)]")
                        }
                    } else if let exception = task.exception {
                        print("download failed: [\(exception)]")
                    } else {
                        dispatch_async(dispatch_get_main_queue(), { () -> Void in
                            if let index = self.indexOfDownloadRequest(self.downloadRequests, downloadRequest: downloadRequest) {
                                self.downloadRequests[index] = nil
                                self.downloadFileURLs[index] = downloadRequest.downloadingFileURL
    
                                if let data = NSData(contentsOfURL: downloadRequest.downloadingFileURL) {
                                    self.addImage(UIImage(data: data)!)
                                    self.displayNum++
                                }
                            }
                        })
                    }
                    return nil
                })
    
                break
            default:
                break
            }
        }
    }
    
```
CC BY-SA 3.0
2016-03-17T16:02:02.057
23232
2016-03-18T01:28:40.290
2016-03-18T01:28:40.290
question
ios swift objective-c xcode swift2
非同期通信でのUIScrollViewの更新について