Swift 尝试解码json时得到Nil

我正在尝试从以下URL解码Json：

https://api.letsbuildthatapp.com/appstore/featured

让我们从中构建该应用程序教程 这是我写的代码：

import UIKit

class AppCategory: NSObject{
    var name: String?
    var apps: [App]?

    static func fetchedFeaturedApps(){
        let jsonUrlString = "https://api.letsbuildthatapp.com/appstore/featured"
        guard let url = URL(string: jsonUrlString) else {return}
        URLSession.shared.dataTask(with: url) { (data, response, err) in
            guard let data = data else {return}
            do{
                let featured = try JSONDecoder().decode(Featured.self, from: data)
            }catch{
                print(err)
            }
            }.resume()
    }
}

struct Featured: Decodable {
    var bannerCategory: Banner?
    var featuredCategories: [mCategory]?
}
struct Banner: Decodable {
    var name: String?
    var apps: [String]?
    var type: String?
}

struct mCategory: Decodable {
    var name: String?
    var apps: [App]?
    var type: String?
}

struct App: Decodable {
    var id: Int?
    var name: String?
    var category: String?
    var price: Float?
    var imageName: String?
}

我试着按照教程学习，但对我来说不起作用。 在尝试从url解码json时，我总是得到nil。我真的是个新手，不知道自己做错了什么。我知道要正确解码json，我需要有与json相同的结构，就像类别中的应用程序数组一样，但它仍然无法工作

编辑：应该提到，当我运行它时，代码进入catch块并打印nil

我尝试打印“err”，但日志中只显示以下内容：

2019-02-09 19:07:45.241000+0200 AppStore[2344:120273] [AXMediaCommon] Unable to look up screen scale
2019-02-09 19:07:45.241153+0200 AppStore[2344:120273] [AXMediaCommon] Unexpected physical screen orientation
2019-02-09 19:07:45.314112+0200 AppStore[2344:120273] [AXMediaCommon] Unable to look up screen scale
2019-02-09 19:07:45.319977+0200 AppStore[2344:120273] [AXMediaCommon] Unable to look up screen scale
2019-02-09 19:07:45.320189+0200 AppStore[2344:120273] [AXMediaCommon] Unexpected physical screen orientation
nil

你有

typeMismatchSwift.String，Swift.DecodingError.ContextcodingPath:[CodingKeyStringValue:bannerCategory，intValue:nil]，debugDescription:应解码字符串，但找到了字典，UnderingError:nil

你需要

struct Featured: Codable {
    let bannerCategory: BannerCategory
    let categories: [Category]
}

struct BannerCategory: Codable {
    let name: String
    let apps: [BannerCategoryApp]
    let type: String
}

struct BannerCategoryApp: Codable {
    let imageName: String

    enum CodingKeys: String, CodingKey {
        case imageName = "ImageName"
    }
}

struct Category: Codable {
    let name: String
    let apps: [CategoryApp]
    let type: String
}

struct CategoryApp: Codable {
    let id: Int?
    let name, category: String?
    let price: Double?
    let imageName: String

    enum CodingKeys: String, CodingKey {
        case id = "Id"
        case name = "Name"
        case category = "Category"
        case price = "Price"
        case imageName = "ImageName"
    }
}

---

你怎么知道是零？你有印刷特色吗？do/catch中是否有错误？它将进入catch并打印nil。我应该提一下。我现在要补充。很抱歉，因为存在PrintError，所以出现错误？你介意展示一下印刷品吗？因为里面有很多信息。我把日志添加到OP中，但我不认为这有什么帮助，因为它也只显示了nil。根据回答，没有，发现了一个错误。从哪里可以得到nil，下面你需要一个补全它直接进入catch块。请去掉所有的结构并用答案中的内容进行测试。我试图调试，这是它写的问题：debugDescription String没有与key codingkeystringvalue:\Name\，intValue:nil\Name\关联的值。好吧，刚刚再次检查，它现在正在工作，我猜问题在于JSON中的一些应用程序的价格为零，因为它是“免费应用”，所以CategoryApp中的价格是可选的。谢谢

class AppCategory: NSObject{
    var name: String?
    var apps: [CategoryApp]?

    static func fetchedFeaturedApps(){
        let jsonUrlString = "https://api.letsbuildthatapp.com/appstore/featured"
        guard let url = URL(string: jsonUrlString) else {return}
        URLSession.shared.dataTask(with: url) { (data, response, err) in
            guard let data = data else {return}
            do{
                let featured = try JSONDecoder().decode(Featured.self, from: data)
                print(featured)
            }catch{
                print(error)
            }
            }.resume()
    }
}