将 NSURLConnection 更改为 NSURLSession 后加载图像很慢

Question

我在 iOS 8 中有一个用于加载图像的代码，而且速度非常快。

if let url = NSURL(string: urlString) {
        let request = NSURLRequest(URL: url)
        NSURLConnection.sendAsynchronousRequest(request, queue: NSOperationQueue.mainQueue()) {
            (response: NSURLResponse?, data: NSData?, error: NSError?) -> Void in
            self.image = UIImage(data: data!)
        }
    }

然后 iOS 9 出来了，我为此苦苦挣扎

let session = NSURLSession.sharedSession()
    let urlString = urlString
    let url = NSURL(string: urlString)
    let request = NSURLRequest(URL: url!)
    let dataTask = session.dataTaskWithRequest(request) { (data:NSData?, response:NSURLResponse?, error:NSError?) -> Void in
        self.image = UIImage(data: data!)
    }
    dataTask.resume()

图片加载速度很慢。

Answer 1

在dataTaskWithRequest 闭包中，您必须在主线程上更新图像。这样做：

let dataTask = session.dataTaskWithRequest(request) { (data:NSData?, response:NSURLResponse?, error:NSError?) -> Void in
    dispatch_async(dispatch_get_main_queue()) {
        self.image = UIImage(data: data!)
    }
}