使用NSURLConnection下载渐进式JPG

Question

我目前正在尝试创建一个渐进式JPG加载器。当一个大图像传递到我的NSURLConnection时，它似乎会将图像的一半切掉。

这是我的didReceiveData方法和数据分配给的图像：

func connection(connection: NSURLConnection!, didReceiveData data: NSData!){
    if let img: UIImage = UIImage(data: data){
        imageView.image = img
    }
    print("didReceiveData")
}

似乎跳过最后一块数据来完成图像。示例图像是：

此图片已完成传递给connectionDidFinishLoading，但显然不是。任何人都有任何关于为什么会发生这种情况的想法？

Answer 1

委托optional public func connection(connection: NSURLConnection, didReceiveData data: NSData)假设是回调以递增方式加载数据。每次调用时，您都会收到新的可用数据。因此，如果您尝试使用接收的数据设置创建图像，则不会是已完成的图像。相反，你应该尝试这个

@IBOutlet weak var imageView: UIImageView!
    var receivedData = NSMutableData()

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        let imageURL = "https://www.nasa.gov/sites/default/files/styles/full_width_feature/public/thumbnails/image/leisa_christmas_false_color.png?itok=75o-jlD5";
        let request = NSURLRequest(URL: NSURL(string: imageURL)!)
        let urlConnection = NSURLConnection(request: request, delegate: self, startImmediately: true)
        urlConnection?.start()
    }

extension ViewController: NSURLConnectionDelegate, NSURLConnectionDataDelegate {

    func connection(connection: NSURLConnection, didReceiveData data: NSData) {
        self.receivedData.appendData(data)
    }

    func connectionDidFinishLoading(connection: NSURLConnection) {
        self.imageView.image = UIImage(data: receivedData)
    }
}

我希望这会对你有所帮助。