Question

我在我的应用程序中创建了一个活动指示器：

  @IBAction func LocateMe(sender: AnyObject) {
    Loading.hidden = false
    Loading.startAnimating()

}

隐藏了ViewDidLoad，当我点击LocateMe按钮时，我想开始在屏幕上看到它加载。问题是它开始加载但很晚，它在应用程序打开下一个视图控制器时启动。您有任何想法，一旦用户点击按钮，我怎么能开始在屏幕上显示它。如果用户等待并且没有指示器向他显示操作已完成，则它是无用的。我也是开放的例子。

import UIKit
import MapKit
import CoreLocation
import SwiftyJSON
import SVProgressHUD

 struct City {

let name : String
let location : CLLocation
let description :String
let imageName : NSURL
let fileLink : NSURL

func distanceTo(location:CLLocation) -> Int
{
    let distanceMeters = location.distanceFromLocation(self.location)
    let distanceKilometers = distanceMeters / 1000.00
    return Int(round(100 * distanceKilometers) / 100)
}
}

class FirstViewController: UIViewController, CLLocationManagerDelegate {

@IBOutlet weak var Loading: UIActivityIndicatorView!
@IBOutlet weak var LocateMeButton: UIButton!
@IBOutlet weak var LabelTest: UILabel!
@IBOutlet weak var Slider: UISlider!
@IBOutlet weak var LabelValueSlider: UILabel!
var MySliderCurrentValue = Double()

var locationManager = CLLocationManager()

var userLoc : CLLocation!
var cities = [City]()
var nearbyCities = [City]()

override func viewDidLoad() {
    super.viewDidLoad()

    Loading.hidden = true
    LocateMeButton.layer.cornerRadius = 5

    // Do any additional setup after loading the view, typically from a nib.

    // let path: String = NSBundle.mainBundle().pathForResource("cities", ofType: "json") as String!
    let path = NSData(contentsOfURL: NSURL(string: "http://www.99website.eu/citiescopy.json")!) as NSData!
    // let jsonData = NSData(contentsOfFile: path) as NSData!
    var error : NSError?
    let ReadableJSON2 = JSON ( data:path, options: NSJSONReadingOptions.MutableContainers, error: &error )
    print(error)

    do {
        let jsonObject = try NSJSONSerialization.JSONObjectWithData(path!, options: NSJSONReadingOptions.MutableContainers) as! [String:AnyObject]
        for city in jsonObject["cities"] as! [[String:AnyObject]] {
            //let coordinates = position["Position"] as! [String:CLLocationDegrees]
            let cityName = city["Name"] as! String
            let latitude = city["Latitude"] as! Double
            let longitude = city["Longitude"] as! Double
            let description = city["Description"] as! String
            let image = city["Image"] as! String
            let lin = city["Link"] as! String
            let location = CLLocation(latitude: latitude, longitude: longitude)
            let city = City(name: cityName, location: location,description: description, imageName: NSURL( string: image )!, fileLink: NSURL( string: lin )! )

            cities.append(city)

        }

    } catch let error as NSError {
        print(error)
    }


    locationManager.delegate = self
    locationManager.desiredAccuracy = kCLLocationAccuracyBest
    locationManager.distanceFilter = kCLDistanceFilterNone
    locationManager.requestWhenInUseAuthorization()
    locationManager.startMonitoringSignificantLocationChanges()
    locationManager.startUpdatingLocation()

    if locationManager.respondsToSelector(#selector(locationManager.requestWhenInUseAuthorization)) {
        locationManager.requestWhenInUseAuthorization()
        locationManager.requestLocation()
    }
    else {
        locationManager.startUpdatingLocation()
    }


}

Answer 1

我认为你的问题是@AsadAli所说的。您在主线程上同步加载数据。您应该尝试将其移动到后台线程（异步），这样您的UI就不会被阻止。

你可以这样做：

/**
 Loads the JSON data asyncrounously

 - parameter urlString:  the URL
 - parameter completion: call on the main thread when the transaction is complete. Returning the data if it's there and an error if one exist.
 */
func loadJSONAsync(urlString: String, completion:(data: NSData?, error: NSError?) ->()) {

    NSURLSession.sharedSession().dataTaskWithURL(NSURL(string: urlString)!, completionHandler: { (data, response, error) -> Void in

        dispatch_async(dispatch_get_main_queue(), { () -> Void in
            if error != nil {
                completion(data: nil, error: error)
            }
            else {
                completion(data: data, error: nil)
            }
        })
    }).resume()
}

然后在viewDidLoad：

中将其称为此内容

    loadJSONAsync("") { (data, error) in

        if let err = error {
            print(err)
        }
        else {
            //process JSON data
        }

    }

只是为了快速清理你的viewDidLoad我会像这样构建它：

override func viewDidLoad() {
    super.viewDidLoad()

    Loading.hidden = true
    LocateMeButton.layer.cornerRadius = 5


    //
    // You should start showing a loading wheel heree
    //

    //Load the JSON
    loadJSONAsync("http://www.99website.eu/citiescopy.json") { (data, error) in

        if let err = error {
            print(err)
        }
        else {
            processJSON(data)
        }
    }

    // Start your location manager
    startLocationManager()

}

func processJSON(data: NSData) {
    var error : NSError?
    let ReadableJSON2 = JSON ( data:path, options: NSJSONReadingOptions.MutableContainers, error: &error )
    print(error)

    do {
        let jsonObject = try NSJSONSerialization.JSONObjectWithData(path!, options: NSJSONReadingOptions.MutableContainers) as! [String:AnyObject]
        for city in jsonObject["cities"] as! [[String:AnyObject]] {
            //let coordinates = position["Position"] as! [String:CLLocationDegrees]
            let cityName = city["Name"] as! String
            let latitude = city["Latitude"] as! Double
            let longitude = city["Longitude"] as! Double
            let description = city["Description"] as! String
            let image = city["Image"] as! String
            let lin = city["Link"] as! String
            let location = CLLocation(latitude: latitude, longitude: longitude)
            let city = City(name: cityName, location: location,description: description, imageName: NSURL( string: image )!, fileLink: NSURL( string: lin )! )

            cities.append(city)

            //
            // You should stop showing a loading wheel heree
            //

        }

    } catch let error as NSError {
        print(error)
    }
}

func startLocationManager() {
    locationManager.delegate = self
    locationManager.desiredAccuracy = kCLLocationAccuracyBest
    locationManager.distanceFilter = kCLDistanceFilterNone
    locationManager.requestWhenInUseAuthorization()
    locationManager.startMonitoringSignificantLocationChanges()
    locationManager.startUpdatingLocation()

    if locationManager.respondsToSelector(#selector(locationManager.requestWhenInUseAuthorization)) {
        locationManager.requestWhenInUseAuthorization()
        locationManager.requestLocation()
    }
    else {
        locationManager.startUpdatingLocation()
    }
}

/**
 Loads the JSON data asyncrounously

 - parameter urlString:  the URL
 - parameter completion: call on the main thread when the transaction is complete. Returning the data if it's there and an error if one exist.
 */
func loadJSONAsync(urlString: String, completion:(data: NSData?, error: NSError?) ->()) {

    NSURLSession.sharedSession().dataTaskWithURL(NSURL(string: urlString)!, completionHandler: { (data, response, error) -> Void in

        dispatch_async(dispatch_get_main_queue(), { () -> Void in
            if error != nil {
                completion(data: nil, error: error)
            }
            else {
                completion(data: data, error: nil)
            }
        })
    }).resume()
}

...你的变量名也应该用小写声明：）

如何在按下按钮后启动活动指示器加载？

1 个答案: