使用NSURLSession下载后,将图像设置为对象

Question

我有7个车对象,我需要下载汽车图像并将其设置为Car对象.

下载完成后我在didFinishDownloadingToURL函数中检索图像,我有两个选择:1.直接从临时文件加载图像2.将文件移动到另一个位置并将其保存在目录中(例如).

问题是我不知道如何将这个后退图像设置为相应的对象!如果我使用第一个选项,我怎样才能找到好的和相应的对象来设置图像？

或者,如果我使用seconde选项:将文件保存到目录,如何找到相应的图像文件并将其设置为相应的对象？

实际上我使用NSURLSession从不同的网址下载图像.为此,我有管理URLSession回调的DownloadSessionDelegate.在这里你可以找到我的课程:

typealias CompleteHandlerBlock = () -> ()
class DownloadSessionDelegate: NSObject, NSURLSessionDelegate, NSURLSessionDownloadDelegate {

var handlerQueue : [String : CompleteHandlerBlock]!

class var sharedInstance:DownloadSessionDelegate {

    struct Static {

        static var instance :DownloadSessionDelegate?
        static var token : dispatch_once_t = 0 ;
    }

    dispatch_once(&Static.token) {
        Static.instance = DownloadSessionDelegate();
        Static.instance!.handlerQueue = [String : CompleteHandlerBlock]();
    }

    return Static.instance!
}

// Session delegate
func URLSession(session: NSURLSession, didBecomeInvalidWithError error: NSError?) {
    println("session error: \(error?.localizedDescription).")
}

func URLSession(session: NSURLSession, didReceiveChallenge challenge: NSURLAuthenticationChallenge, completionHandler: (NSURLSessionAuthChallengeDisposition, NSURLCredential!) -> Void) {
    completionHandler(NSURLSessionAuthChallengeDisposition.UseCredential, NSURLCredential(forTrust: challenge.protectionSpace.serverTrust))
}

func URLSession(session: NSURLSession, downloadTask: NSURLSessionDownloadTask, didFinishDownloadingToURL location: NSURL) {
    println("session \(session) has finished the download task \(downloadTask) of URL \(location).")

    var fileHandle:NSFileHandle = NSFileHandle(forReadingAtPath: location.path!)!
    var data:NSData = fileHandle.readDataToEndOfFile()
    var image:UIImage = UIImage(data: data)! }

我还把handleEventsForBackgroundURLSession int AppDelegate放进去,一切都很好.

我有一个也是唯一一个类:UIImageUtils,我有函数调用DownloadImage.每个不同的类都会调用这个功能来下载他们的图像.在这里你找到这个功能:

// Download image
static func downloadImageFromUrl(urlImage:NSString, writeToDevice: Bool, storeName:NSString, object:    AnyObject) {

    var configuration = NSURLSessionConfiguration.backgroundSessionConfiguration(SessionProperties.identifier);
    var backgroundSession = NSURLSession(configuration: configuration, delegate: DownloadSessionDelegate.sharedInstance, delegateQueue: nil);
    var url = NSURLRequest(URL:  NSURL(string: ConfigurationManager.host + urlImage)!);
    var downloadTask = backgroundSession.downloadTaskWithRequest(url);
    downloadTask.resume();

}

非常感谢你的帮助.

Answer 1

而不是使用委托的所有麻烦.您可以使用该downloadTaskWithRequest方法的完成块.我修改了downloadImageFromUrl函数来获取一个块.可以从汽车对象调用此函数,以便在该实例中获得回调.

func downloadImageFromUrl(urlImage:NSString, writeToDevice: Bool, storeName:NSString, object: AnyObject, onfinished:(UIImage) -> ()) {

    var configuration = NSURLSessionConfiguration.backgroundSessionConfiguration(SessionProperties.identifier);
    var backgroundSession = NSURLSession(configuration: configuration, delegate: DownloadSessionDelegate.sharedInstance, delegateQueue: nil);
    var url = NSURLRequest(URL:  NSURL(string: ConfigurationManager.host + urlImage)!);
    var downloadTask = backgroundSession.dataTaskWithRequest(url, completionHandler: {
        data,response,error in

        if error == nil
        {
            if let image = UIImage(data: data)
            {
                dispatch_async(dispatch_get_main_queue(), { () -> Void in

                    onfinished(image)
                })
            }
        }

    })
    downloadTask.resume();

}

在汽车类里面

class Car
{
    func downloadImage
    {
        YourDelegate.downloadImageFromUrl(self.imageUrl, writeToDevice: true, storeName: "store", object: nil, onfinished: { downloadedImage in
            self.image = downloadedImage
        })
    }
}