ios - 从进入主队列后，UI 变得无响应

Question

我正在尝试从 url 延迟加载图像并在仅在主队列中接收到图像后更新 UI，UI 正在更新但 View 变得无响应，我正在使用 GCD 创建一个新的从 URL 获取数据的线程

让 imageUrl : NSURL = NSURL(string: SiteAPIURL + (DEFAULTS.valueForKey(kInviterImageUrl) as!String))!

    let request: NSURLRequest = NSURLRequest(URL: imageUrl)
    SwiftLoader.show(title: "Loading", animated: true)


    let queue  : dispatch_queue_t = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0)

  dispatch_async(queue) { () -> Void in
    let data : NSData = NSData(contentsOfURL: imageUrl)!
    let image = UIImage(data: data)!
    dispatch_async(dispatch_get_main_queue(), { () -> Void in
        self.userImage.image   = image
        self.userImageWide.image = image

    })



    }

Answer 1

“DISPATCH_QUEUE_PRIORITY_HIGH:分派(dispatch)到队列的项目以高优先级运行；队列被安排在任何默认优先级或低优先级队列之前执行。”那是文档中的内容，因此请使用优先级较低的其他内容，因为这可能会阻塞默认队列，例如 QOS_CLASS_USER_INITIATED。这就是你想要的

    if let url = imageUrl{
        let qos = Int(QOS_CLASS_USER_INITIATED.rawValue)
        dispatch_async(dispatch_get_global_queue(qos, 0), {
            let data = NSData(contentsOfURL: imageUrl)
            dispatch_async(dispatch_get_main_queue(), {
                if data != nil {
                    if let image = UIImage(data: data){
                        self.userImage.image   = image
                        self.image = UIImage(data: imageData!)
                        self.userImageWide.image = image
                    }
                }
            })
        })
    }