php – Swift异步数据显示滞后

我从服务器(我通过一些 PHP Web服务访问的MysqL数据库)获取异步数据时遇到了一些困难.我的代码如下：

func RetreiveStaff() {
    SetProgramMode()

    self.astrUsers = [String]()
    self.pkvUser.reloadAllComponents()

    if self.booCurrentDataVersion == true {

        var url:NSURL = NSURL(string: "http://www.website.com.au/retrievestaff.PHP")!
        let task:NSURLSessionDataTask = NSURLSession.sharedSession().dataTaskWithURL(url,completionHandler: { (data:NSData!,response:NSURLResponse!,error:NSError!) -> Void in
            if error == nil {
                let dataArray:[AnyObject] = NSJSONSerialization.JSONObjectWithData(data,options: NSJSONReadingOptions.MutableContainers,error: nil) as! [AnyObject]
                for data in dataArray {
                    let dictionary:[String:String] = data as! [String:String]
                    if dictionary["StaffID"] != nil {
                        self.astrUsers.append(dictionary["LastName"]! + "," + dictionary["FirstName"]!)
                        self.astrUserIDs.append(dictionary["StaffID"]!)
                        self.pkvUser.reloadAllComponents()
                    }
                    self.pkvUser.reloadAllComponents()
                }
            } else {
                let actionSheet:UIAlertController = UIAlertController(title: "Connection Error",message: "\(strAppName) was unable to load data.  Check you are connected to the internet and restart the app.",preferredStyle: UIAlertControllerStyle.Alert)
                let firstAlertAction:UIAlertAction = UIAlertAction(title: "OK",style: UIAlertActionStyle.Default,handler: {
                    (alertAction:UIAlertAction!) in
                })
                actionSheet.addAction(firstAlertAction)
                self.presentViewController(actionSheet,animated: true,completion: nil)
            }
        })

        task.resume()

    }
}

代码执行时,将按原样获取数据,但视图不会显示它.基本上,正如您所看到的,我抓取数据,将其放入数组中,然后重新加载我的pickerView(它使用数组作为其数据源).执行代码后,pickerView在约20秒内保持明显空白,然后突然出现.但是,如果用户在20秒内点击,拖动,更改pickerView等的值,则会显示数据.

根据我对问题的理解,这意味着数据被提取并放入pickerView,但视图没有正确地重新加载,尽管我的数量很多且可能是过多的self.pkvUser.reloadAllComponents().

我究竟做错了什么？

(我也检查过这些问题,但他们没有解决这个问题：

Swift: Asynchronous callback
Asynchronous Fetching Swift Xcode
iOS Swift: Displaying asynchronous data on a TableView)

解决方法

在IOS中显示任何视图应该始终在主线程中.

当您执行异步请求时,将结果从主线程推送到用户的视图,如下所示：

var someView : UIView  = someAsyncCallBack..
 dispatch_async(dispatch_get_main_queue()) {
    currentView.addSubview(someView);
 }

尝试这段代码,在异步请求完成后,处理主队列中的响应没有问题,这也解决了显示滞后问题

if error == nil {
    dispatch_async(dispatch_get_main_queue()) {
        let dataArray:[AnyObject] = NSJSONSerialization.JSONObjectWithData(data,error: nil) as! [AnyObject]
        for data in dataArray {
            let dictionary:[String:String] = data as! [String:String]
            if dictionary["StaffID"] != nil {
                self.astrUsers.append(dictionary["LastName"]! + "," + dictionary["FirstName"]!)
                self.astrUserIDs.append(dictionary["StaffID"]!)
                self.pkvUser.reloadAllComponents()
            }
            self.pkvUser.reloadAllComponents()
        }
    }
}