解析 JSON - “变量‘jsonObject’在初始化之前使用

Question

我在用于 iOS 9.0 项目、在 Xcode 7 beta 5 上、在 OS X El Cap 上运行的 JSON 库时遇到问题。

我跟随this link 制作了我的应用程序的一部分，其中涉及一些基本的 MapKit 功能。在这个“部分”中，我必须将 JSON 数据解析为“问题位置”（它是校报的应用程序，我们将拥有一张他们发布问题的所有位置的地图）。

这是我的问题（我不明白，因为我是初学者 iOS 开发人员）。我在下一行收到错误消息，上面写着“在初始化之前使用了变量 'jsonObject'”。

有问题的行是“loadInitialData”函数中的第三个“段落”。

if let jsonObject = jsonObject as? [String: AnyObject],

这是我的“MapViewController.swift”文件的所有代码，用于管理我的 MapKit 视图中发生的所有事情。

import UIKit
import MapKit
import CoreLocation

class MapViewController: UIViewController, CLLocationManagerDelegate, MKMapViewDelegate {

// Map View outlet declaration
@IBOutlet weak var mapView: MKMapView!

// Hamburger button declaration
@IBOutlet weak var menuButton:UIBarButtonItem!

var locationManager: CLLocationManager?

// Creating a variable to hold the "IssueLocation" objects from the JSON file
var issueLocations = [IssueLocation]()

override func viewDidLoad() {
    super.viewDidLoad()

    // Hamburger button configuration
if self.revealViewController() != nil {
    menuButton.target = self.revealViewController()
    menuButton.action = "revealToggle:"
    self.view.addGestureRecognizer(self.revealViewController().panGestureRecognizer())
    }

    // Setting the Map type to standard
    mapView.mapType = MKMapType.Standard

    // Configuring locationManager and mapView delegate
    locationManager = CLLocationManager()
    mapView.delegate = self

    // Set the center of campus as the first location, before we show the actual user location
    let initialLocation = CLLocation(latitude: 44.226397, longitude: -76.495571)
    let regionRadius: CLLocationDistance = 1000

    // Centering map on center of campus
    func centerMapOnLocation(location: CLLocation) {
        let coordinateRegion = MKCoordinateRegionMakeWithDistance(location.coordinate, regionRadius * 2.0, regionRadius * 2.0)
        mapView.setRegion(coordinateRegion, animated: true)
    }

    loadInitialData()
    mapView.addAnnotations(issueLocations)

    // Show user location and start updating user location
    mapView.showsUserLocation = true
    locationManager?.startUpdatingLocation()

//        // Show a sample issue location on the Map
//        let IssueLocation = IssueLocation(locationName: "Stirling Hall, West  Entrance", coordinate: CLLocationCoordinate2D(latitude: 44.22468034747186, longitude: -76.49805217981339))
//        
//        mapView.addAnnotation(IssueLocation)

    // Do any additional setup after loading the view.
}

func mapView(mapView: MKMapView, didUpdateUserLocation userLocation: MKUserLocation) {
    mapView.centerCoordinate = userLocation.location!.coordinate
}

func loadInitialData() {

    let fileName = NSBundle.mainBundle().pathForResource("IssueLocations", ofType: "json");
    var readError : NSError?
    var data: NSData?

    do {
        data = try NSData(contentsOfFile: fileName!, options: NSDataReadingOptions(rawValue: 0))
    } catch _ {
        data = nil
    }

    var error: NSError?
    let jsonObject: AnyObject!
    if let data = data {

        do {
            jsonObject = try NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions(rawValue: 0))
        } catch _ {
            jsonObject = nil
        }

    }

    if let jsonObject = jsonObject as? [String: AnyObject],
        let jsonData = JSONValue.fromObject(jsonObject)?["data"]?.array {
            for issueLocationJSON in jsonData {
                let issueLocation = IssueLocation.fromJSON(issueLocationJSON.array!)
                        issueLocations.append(issueLocation)



            }

    }
}

// Checking location authorization status and requesting permission from user if status is not ".AuthorizedWhenInUse"
func checkLocationAuthorizationStatus() {

    if CLLocationManager.authorizationStatus() == .AuthorizedWhenInUse {
        mapView.showsUserLocation = true
     } else {
        locationManager?.requestWhenInUseAuthorization()
        }
    }

override func viewDidAppear(animated: Bool) {
    super.viewDidAppear(animated)
    checkLocationAuthorizationStatus()
    }

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}


/*
// MARK: - Navigation

// In a storyboard-based application, you will often want to do a little preparation before navigation
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
// Get the new view controller using segue.destinationViewController.
// Pass the selected object to the new view controller.
}
*/


}

Answer 1

如果if let data = data 计算结果为false，则jsonObject 将不会被初始化，因为该对象的所有初始化都发生在该 if 语句中。尝试在创建变量时将jsonObject 初始化为nil。