解析JSON-在初始化之前使用“變量'jsonObject'

Question

我在運行於OS X El Cap的Xcode 7 beta 5上的iOS 9.0項目中使用的JSON庫存在問題。

我點擊了此鏈接 ，使我的應用程序包含了一些基本的MapKit功能。 在此“部分”中，我必須將JSON數據解析為“問題位置”（這是一份學校報紙的應用程序，我們將獲得所有問題發生地點的地圖）。

這是我的問題（因為我是iOS初學者，所以我不理解）。 我在下一行收到錯誤消息，提示“初始化前使用了變量'jsonObject'”。

該行是“ loadInitialData”函數中的第三個“段落”。

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

這是“ MapViewController.swift”文件的所有代碼，用於管理MapKit視圖中發生的所有事情。

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計算結果為false ，則不會初始化jsonObject因為該對象的所有初始化都在if語句內進行。 創建變量時，嘗試將jsonObject初始化為nil 。