在 Swift 中使用 JSONDecoder 时，我不断收到 "No value associated with key" 错误。有人可以解释这里出了什么问题吗？

Question

我正在尝试从本地 JSON 文件中读取并使用要从 Decoder 检索的单元格填充我的 table 视图。由于我的 table 视图仍然是空的，我在 JSONDecoder.decode 行上添加了一个断点以查看发生了什么。我得到这个错误，即使我确保我的命名约定在我的结构和 JSON 文件中是相同的。我在这里遗漏了什么吗？

由于我的命名约定在文件中是一致的，起初我没有尝试在我的结构中添加 CodingKeys enum。在几次失败运行之后，我添加了它，但感觉有点过时了。

我在哪里运行解码器：

let fileName = "settings"

...


   if let url = Bundle.main.url(forResource: fileName, withExtension: "json") {
       do {
            let data = try Data(contentsOf: url)
            let list = try JSONDecoder().decode(SettingsPayload.self, from: data)
            completion(list.sections)
       } catch {
            completion(nil)
       }
   }

fileprivate struct SettingsPayload: Decodable {
    let sections: [Section]
}

检索时将用于存储数据的我的结构：

struct Item: Decodable {
    let title: String
    let type: String
    let url: String

    private enum CodingKeys: String, CodingKey {
        case title = "title"
        case type = "type"
        case url = "url"
    }
}

struct Section: Decodable {
    let title: String
    let items: [Item]

    private enum CodingKeys: String, CodingKey {
        case title = "title"
        case items = "items"
    }
}

和我的 .json 文件：

{
    "sections": [{
        "section": {
            "title": "Main Settings",
            "items": [{
                "item": {
                    "title": "Notifications",
                    "type": "notification",
                    "url": ""
                },
                "item": {
                    "title": "Log Out",
                    "type": "",
                    "url": ""
                }
            }]
        },
        "section": {
            "title": "Feedback",
            "items": [{
                "item": {
                    "title": "Contact Us",
                    "type": "email",
                    "url": ""
                },
                "item": {
                    "title": "Rate on App Store",
                    "type": "webView",
                    "url": "https://www.apple.com/uk/ios/app-store/"
                }
            }]
        },
        "section": {
            "title": "About",
            "items": [{
                "item": {
                    "title": "Terms of Service",
                    "type": "webView",
                    "url": ""
                },
                "item": {
                    "title": "Privacy Policy",
                    "type": "webView",
                    "url": "https://www.apple.com/uk/ios/app-store/"
                },
                "item": {
                    "title": "Version Info",
                    "type": "webView",
                    "url": ""
                }
            }]
        }
    }]
}

这是我收到的错误消息：

     - debugDescription : "No value associated with key CodingKeys(stringValue: \"title\", intValue: nil) (\"title\")."

Answer 1

我认为问题在于解码器需要项目部分的数组，但你的 json 有一个字典数组，其中有一个键 "section" 和一个项目部分。

也许可以尝试像这样修改您的 json：

{
    "sections": [{
            "title": "Main Settings",
            "items": [ {
                    "title": "Notifications",
                    "type": "notification",
                    "url": ""
                }, {
                    "title": "Log Out",
                    "type": "",
                    "url": ""
                }]}, {
            "title": "Feedback",
            "items": [{
                    "title": "Contact Us",
                    "type": "email",
                    "url": ""
                },{
                    "title": "Rate on App Store",
                    "type": "webView",
                    "url": "https://www.apple.com/uk/ios/app-store/"
                }]}, {
            "title": "About",
            "items": [{
                    "title": "Terms of Service",
                    "type": "webView",
                    "url": ""
                }, {
                    "title": "Privacy Policy",
                    "type": "webView",
                    "url": "https://www.apple.com/uk/ios/app-store/"
                }, {
                    "title": "Version Info",
                    "type": "webView",
                    "url": ""
                }
  ]}]
}

更新

JSON解码器不会在 JSON 中查找可解码结构的名称，它只会查找属性的名称。

在 Swift 中使用 JSONDecoder 时，我不断收到 "No value associated with key" 错误。有人可以解释这里出了什么问题吗？

I keep getting the "No value associated with key" error when using the JSONDecoder in Swift. Can someone please explain what is going wrong here?

json

ios

swift

codable