ios - 异步 Web 请求后无法让事件指示器停止

Question

我需要事件指示器在发出网络请求时启动并在完成后停止。现在指示器将显示，但 .stopAnimation 甚至立即执行，而不等待 Web 请求完成。

import UIKit


class ViewController: 
UIViewController,UIPickerViewDelegate,UIPickerViewDataSource {

@IBOutlet weak var locationPickerOutlet: UIPickerView!
@IBOutlet weak var theProgressOutlet: UIActivityIndicatorView!

var locationspickerData: [String] = [String]()

override func viewDidLoad() {
    super.viewDidLoad()

    populateLocations()

}


func populateLocations() {

    self.locationspickerData = ["All Locations"]
    let url:URL = URL(string: "http://<web address>")!
    let session = URLSession.shared
    let request = NSMutableURLRequest(url: url)
    request.httpMethod = "GET"
    //request.cachePolicy = NSURLRequest.CachePolicy.reloadIgnoringCacheData
    let task = session.dataTask(with: request as URLRequest, completionHandler: {
        (data, response, error) in
        guard let _:Data = data, let _:URLResponse = response  , error == nil else {
            return
        }

        let json: Any?
        do
        {
            json = try JSONSerialization.jsonObject(with: data!, options: [])
        }
        catch
        {
            return
        }
        guard let data_list = json as? NSArray else
        {
            return
        }
        if let locations_list = json as? NSArray
        {

            for i in 0 ..< data_list.count
            {
                if let locations_obj = locations_list[i] as? NSDictionary
                {
                    if let location_name = locations_obj["name"] as? String
                    {
                        self.locationspickerData.append(location_name)
                    }
                }
            }


            self.locationPickerOutlet.delegate = self
            self.locationPickerOutlet.dataSource = self
            DispatchQueue.main.asyncAfter(deadline: .now() + 0.01) {
                self.theProgressOutlet.stopAnimating()
            }

        }

    })

    task.resume()

}



override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
}


func numberOfComponents(in pickerView: UIPickerView) -> Int {
    return 1
}

func pickerView(_ pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {
    return locationspickerData.count
}


func pickerView(_ pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {
    return locationspickerData[row]
}

func pickerView(_ pickerView: UIPickerView, attributedTitleForRow row: Int, forComponent component: Int) -> NSAttributedString? {
    let titleData = locationspickerData[row]
    let myTitle = NSAttributedString(string: titleData, attributes: [NSFontAttributeName:UIFont(name: "Georgia", size: 15.0)!,NSForegroundColorAttributeName:UIColor.blue])
    return myTitle
}

Answer 1

在DispatchQueue后面添加代码self.theProgressOutlet.stopAnimating()。试试这个

DispatchQueue.main.asyncAfter(deadline: .now() + 0.01) {
//Your code    
            }
self.theProgressOutlet.stopAnimating()

尝试一下，看看是否有效。