swift - 异步中的 ActivityIndi​​cator - Swift

Question

我有大量代码 - 异步加载图像。 I am using Grand Central Dispatch ,但事件指示器不起作用。请帮我找出错误

func loadImage() {
    if let imageUrl = NSURL(string: "http://\($url)/1.jpg") {
        let imageRequest: NSURLRequest = NSURLRequest(URL: imageUrl)
        let queue: NSOperationQueue = NSOperationQueue.mainQueue()
        NSURLConnection.sendAsynchronousRequest(imageRequest, queue: queue, completionHandler:{ (response: NSURLResponse!, data: NSData!, error: NSError!) -> Void in
            if data != nil {
                self.image = UIImage(data: data)!
                self.productImageView.image = self.image

            }
        })
    }
}


override func viewDidLoad() {
    super.viewDidLoad()

    self.imageActivityIndicator.startAnimating()
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), { () -> Void in

    self.loadImage()

    dispatch_async(dispatch_get_main_queue(), { () -> Void in
        self.imageActivityIndicator.stopAnimating()
    })
    });


}

Answer 1

发生这种情况是因为您在 viewDidLoad 中使用 imageActivityIndi​​cator 并且 View 尚未添加到主视图中，因此如果您移动，您的代码是否可以工作它到 viewWillAppear 函数。

另外，当图像加载完成时，您必须隐藏它，因此这使得您的代码如下所示:

func loadImage() {
    if let imageUrl = NSURL(string: "http://skidon.info/1.jpg") {
        let imageRequest: NSURLRequest = NSURLRequest(URL: imageUrl)
        let queue: NSOperationQueue = NSOperationQueue.mainQueue()
        NSURLConnection.sendAsynchronousRequest(imageRequest, queue: queue, completionHandler:{ (response: NSURLResponse!, data: NSData!, error: NSError!) -> Void in
            if data != nil {

                self.image = UIImage(data: data)!
                self.productImageView.image = self.image

                dispatch_async(dispatch_get_main_queue(), { () -> Void in
                    self.imageActivityIndicator.stopAnimating()
                    self.imageActivityIndicator.hidden = true
                })

            }
        })
    }
}


override func viewWillAppear() {
    super.viewWillAppear()

    self.imageActivityIndicator.startAnimating()
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), { () -> Void in

        self.loadImage()

    });


}