xcode 展开可选值时意外发现nil，即使该值已分配值

sulc1iza 于 2023-02-09 发布在其他

关注(0)|答案(3)|浏览(126)

我正在使用Swift从冠状病毒API获取JSON。但是当我尝试运行代码时，我得到了这个错误。
致命错误：展开可选值时意外发现nil：第22行
我的代码是

override func viewDidLoad() {
        super.viewDidLoad()
        
        let url = "https://api.coronavirus.data.gov.uk/v1/data?filters=areaType=nation;areaName=england&structure={%22date%22:%22date%22,%22areaName%22:%22areaName%22,%22areaCode%22:%22areaCode%22,%22newCasesByPublishDate%22:%22newCasesByPublishDate%22,%22cumCasesByPublishDate%22:%22cumCasesByPublishDate%22,%22newDeathsByDeathDate%22:%22newDeathsByDeathDate%22,%22cumDeathsByDeathDate%22:%22cumDeathsByDeathDate%22}"
        getData(from: url)
        // Do any additional setup after loading the view.
    }
    
    private func getData(from url: String) {
        
        let getfromurl = URLSession.shared.dataTask(with: URL(string: url)!, completionHandler: {data, response, error in
            guard let data = data, error == nil else{
                print("Something Went Wrong")
                return
            }
            
            //Have data
            var result: Response?
            do {
                result = try JSONDecoder().decode(Response.self, from: data)
            }
            catch{
                print("failed to convert \(error.localizedDescription)")
            }
            
            guard let json = result else {
                return
            }
            
            print(json.data.date)
        })
        getfromurl.resume()
    
    }

第22行为：

let getfromurl = URLSession.shared.dataTask(with: URL(string: url)!, completionHandler: {data, response, error in

我很困惑，因为我认为这意味着url没有分配任何内容，但即使调试器也认为它有。

- 更新日期：**

我可以获取数据，但获取后出现错误。错误为：
无法转换值NotFound（Swift.Int、Swift.DecodingError.上下文（编码路径：[编码键（字符串值："数据"，整数值：nil）、_JSONKey（字符串值："索引0"，整数值：0）、编码键（字符串值："按死亡日期的新死亡"，整数值：nil）]，调试说明："应为Int值，但找到null。"，underlyingError：无））
转换失败表明在解码JSON和值时出错。

xcode

来源：https://stackoverflow.com/questions/66017912/unexpectedly-found-nil-while-unwrapping-an-optional-value-even-though-it-has-a-v

3条答案

按热度按时间

mw3dktmi1#

该异常并不意味着url就是nil，但是URL(string:url)就是nil
您需要检查url字符串是否为有效的url：

private func getData(from url: String) {
    guard let theURL = URL(string: url) else { print ("oops"); return }
    let getfromurl = URLSession.shared.dataTask(with: theURL, completionHandler: {data, response, error in
       /* ... */
    }
}

更新

由于现在给出了url字符串：问题出在花括号上它们在RFC1738中被标记为 * unsafe *，并且应该被%7b（打开）和%7d（关闭）替换，因此：

let url = "https://api.coronavirus.data.gov.uk/v1/data?filters=areaType=nation;areaName=england&structure=%7b%22date%22:%22date%22,%22areaName%22:%22areaName%22,%22areaCode%22:%22areaCode%22,%22newCasesByPublishDate%22:%22newCasesByPublishDate%22,%22cumCasesByPublishDate%22:%22cumCasesByPublishDate%22,%22newDeathsByDeathDate%22:%22newDeathsByDeathDate%22,%22cumDeathsByDeathDate%22:%22cumDeathsByDeathDate%22%7d"

let theUrl = URL(string: url)
print (theUrl)

这也是official API documentation中的一个示例：

curl -si 'https://api.coronavirus.data.gov.uk/v1/data?filters=areaType=nation;areaName=england&structure=%7B%22name%22:%22areaName%22%7D'

赞(0）回复(0）举报 2023-02-09

bn31dyow2#

URL编码不正确。浏览器有自己的方式来编码URL，但URL(string:根本不进行任何编码。
对于这种复杂的URL，建议使用URLComponents/URLQueryItem创建它。URLComponents的好处是它可以代表您处理编码

let structure = """
{"date":"date","areaName":"areaName","areaCode":"areaCode","newCasesByPublishDate":"newCasesByPublishDate","cumCasesByPublishDate":"cumCasesByPublishDate","newDeathsByDeathDate":"newDeathsByDeathDate","cumDeathsByDeathDate":"cumDeathsByDeathDate"}
"""

var components = URLComponents(string: "https://api.coronavirus.data.gov.uk")!
components.path = "/v1/data"
components.queryItems = [URLQueryItem(name: "filters", value: "areaType=nation;areaName=england"),
                         URLQueryItem(name: "structure", value: structure)]

if let url = components.url {
    print(url)
}

旁注：

- 从不**在JSONDecoder catch块中打印error.localizedDescription。它只向您显示无意义的一般错误消息。始终为print(error)

赞(0）回复(0）举报 2023-02-09

ghhkc1vu3#

在getData方法中进行了更改，请尝试一次

private func getData(from url: String) {
    
    guard let validUrl  = URL(string: url) else {
        return
    }
    let getfromurl = URLSession.shared.dataTask(with: validUrl, completionHandler: {data, response, error in
        guard let data = data, error == nil else{
            print("Something Went Wrong")
            return
        }
        
        //Have data
        var result: Response?
        do {
            result = try JSONDecoder().decode(Response.self, from: data)
        }
        catch{
            print("failed to convert \(error.localizedDescription)")
        }
        
        guard let json = result else {
            return
        }
        
        print(json.data.date)
    })
    getfromurl.resume()

}

赞(0）回复(0）举报 2023-02-09

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xcode 展开可选值时意外发现nil，即使该值已分配值

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