Question

我一直在创建一个从JSON脚本中检索对象的函数。我选择使用alamofire进行异步请求，使用swiftyJSON进行简单的解析。但是我似乎有阻止UI的问题？为什么它是异步请求呢？我是否需要在单独的线程上运行它或者解释是什么？

基本上我的意思是阻止UI是在下面的函数执行完毕之前它不会对其他按钮做出反应。

func getRecent() {


    var url = "http://URL/recent.php?lastid=\(lastObjectIndex)&limit=\(numberOfRecordsPerAPICall)"


    isApiCalling = true
    request(.GET, url, parameters: nil)
        .response { (request, response, data, error) in
            if error == nil {

        let data: AnyObject = data!
        let jsonArray = JSON(data: data as! NSData)
        if jsonArray.count < self.numberOfRecordsPerAPICall {
            self.recentCount = 0
            self.tableVIew.tableFooterView = nil
        } else {
            self.recentCount = jsonArray.count
            self.tableVIew.tableFooterView = self.footerView
        }
        for (key: String, subJson: JSON) in jsonArray {
            // Create an object and parse your JSON one by one to append it to your array
            var httpUrl = subJson["image_url"].stringValue
            let url = NSURL(string: httpUrl)
            let data = NSData(contentsOfURL: url!)

            if UIImage(data: data!) != nil {

            // Create an object and parse your JSON one by one to append it to your array
            var newNewsObject = News(id: subJson["id"].intValue, title: subJson["title"].stringValue, link: subJson["url"].stringValue, imageLink: UIImage(data: data!)!, summary: subJson["news_text"].stringValue, date: self.getDate(subJson["date"].stringValue))







            self.recentArray.append(newNewsObject)

            }
        }

        self.lastObjectIndex = self.lastObjectIndex + self.numberOfRecordsPerAPICall
        self.isApiCalling = false
        self.tableVIew.reloadData()
        self.refreshControl?.endRefreshing()

        }
        }

}

Answer 1

响应闭包在主线程上执行。如果您正在那里进行JSON解析（并且您有大量数据），它将阻塞主线程一段时间。

在这种情况下，您应该使用dispatch_async进行JSON解析，并且仅在完成更新主线程时使用。{/ p>

只需像这样进行解析

func getRecent() {

var url = "http://URL/recent.php?lastid=\(lastObjectIndex)&limit=\(numberOfRecordsPerAPICall)"


isApiCalling = true
request(.GET, url, parameters: nil)
    .response { (request, response, data, error) in
        if error == nil {

    let priority = DISPATCH_QUEUE_PRIORITY_DEFAULT
    dispatch_async(dispatch_get_global_queue(priority, 0)) {

        // Parse stuff here

        let data: AnyObject = data!
        let jsonArray = JSON(data: data as! NSData)
        if jsonArray.count < self.numberOfRecordsPerAPICall {
            self.recentCount = 0
            self.tableVIew.tableFooterView = nil
        } else {
            self.recentCount = jsonArray.count
            self.tableVIew.tableFooterView = self.footerView
        }
        for (key: String, subJson: JSON) in jsonArray {
            // Create an object and parse your JSON one by one to append it to your array
            var httpUrl = subJson["image_url"].stringValue
            let url = NSURL(string: httpUrl)
            let data = NSData(contentsOfURL: url!)

            if UIImage(data: data!) != nil {

            // Create an object and parse your JSON one by one to append it to your array
            var newNewsObject = News(id: subJson["id"].intValue, title: subJson["title"].stringValue, link: subJson["url"].stringValue, imageLink: UIImage(data: data!)!, summary: subJson["news_text"].stringValue, date: self.getDate(subJson["date"].stringValue))

            self.recentArray.append(newNewsObject)
            }
        }

        dispatch_async(dispatch_get_main_queue()) {

            // Update your UI here

            self.lastObjectIndex = self.lastObjectIndex + self.numberOfRecordsPerAPICall
            self.isApiCalling = false
            self.tableVIew.reloadData()
            self.refreshControl?.endRefreshing()
        }
    }
    }
    }
}

Answer 2

Swift5 更新Stefan Salatic的答案，如果您要从Alamofire响应中解析大量json数据，则最好使用全局调度队列，并且如果出于任何原因需要将主线程中的UI更新为DispatchQueue.main .async。

因此示例代码如下所示。

AF.request(UrlGetLayers, method: .post, parameters: parameters, headers: headers)
            .responseJSON { response in
             DispatchQueue.global(qos: .background).async {
                
                //parse your json response here
                
                //oops... we need to update the main thread again after parsing json
                DispatchQueue.main.async {
                    
                }
                
             }

        }

Alamofire http json请求块ui

2 个答案: