Swift:尝试打印CLLocationSpeed时发生异常“解开可选值时意外发现为零". [英] Swift: Exception while trying to print CLLocationSpeed "unexpectedly found nil while unwrapping an Optional value"

问题描述

我正在尝试制作一个超级简单的程序，目前该程序可以从iPhone的gps打印速度.到目前为止，这是我的代码:

I am trying to make a super simple program that will as of right now print the speed from the iPhone's gps. This is my code so far:

//
//  ViewController.swift
//  GpsSpeed
//
//  Created by Jacob Sandum on 4/18/15.
//  Copyright (c) 2015 Jacob Sandum. All rights reserved.
//

import UIKit
import CoreLocation
let locationManager = CLLocationManager()
class ViewController: UIViewController, CLLocationManagerDelegate {

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.
    locationManager.delegate = self
    if CLLocationManager.authorizationStatus() == .NotDetermined {
        locationManager.requestAlwaysAuthorization()
    }
    locationManager.desiredAccuracy=kCLLocationAccuracyBest
    if CLLocationManager.locationServicesEnabled() {
        locationManager.startUpdatingLocation()
    }
  var speed: CLLocationSpeed = CLLocationSpeed()
    speed = locationManager.location.speed
    println(speed);
}

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


}

当我尝试运行此代码时，出现此致命异常:unexpectedly found nil while unwrapping an Optional value (lldb)

When I try to run this code I get this fatal exception: unexpectedly found nil while unwrapping an Optional value (lldb)

我认为CLLocationSpeed为零，但是我不知道该如何解决.

I think CLLocationSpeed is nil, but I do not know how to fix this.

推荐答案

首先将NSLocationAlwaysUsageDescription添加到您的info.plist文件中

First add NSLocationAlwaysUsageDescription in to your info.plist file

那么完整的代码是

 import UIKit
import CoreLocation
class ViewController: UIViewController, CLLocationManagerDelegate {
    let locationManager = CLLocationManager()

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        locationManager.delegate = self
        if NSString(string:UIDevice.currentDevice().systemVersion).doubleValue > 8 {
            locationManager.requestAlwaysAuthorization()
        }
        locationManager.desiredAccuracy=kCLLocationAccuracyBest

    }
    func locationManager(manager: CLLocationManager!, didUpdateLocations locations: [AnyObject]!) {
        var speed: CLLocationSpeed = CLLocationSpeed()
        speed = locationManager.location.speed
        println(speed);
    }
    func locationManager(manager: CLLocationManager!, didChangeAuthorizationStatus status: CLAuthorizationStatus) {
        if status != CLAuthorizationStatus.Denied{
            locationManager.startUpdatingLocation()
        }
    }
}

在真实设备

您的错误:

1. 不要在ViewDidLoad中获得速度，它只会被调用一次.因此，在您的代码中，每次您尝试在开始更新之前获取位置.
2. 最好在位置更新时加快速度
3. 最好在身份验证更改后开始更新

1. Do not get speed in ViewDidLoad it will only be called once.So,in your code, every time you try to get location before it start updating.
2. It is better to get speed when location update
3. It is better to start updating when auth changed

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