如何在 SwiftUI 中使用从 JSON 解码的数据

问题描述

问题

数据从Reddit的api成功解码并放入.onAppear{…}内的变量theUser，但是当我尝试使用它时，我一直得到nil价值.

The data is successfully decoded from Reddit’s api and put into the variable theUser inside the .onAppear {…}, but when I try to use it I keep getting nil values.

代码

struct ContentView: View {
    @State var didAppear = false
    @State var theUser = getNilUser()
    var body: some View {
        Text("User Profile")
        Text(theUser.data.subreddit.display_name_prefixed ?? "No name found")
        .onAppear(perform: {
            theUser = getUser(withName: "markregg")
        })

    }
    func getUser(withName username: String) -> user {
        if !didAppear {
            if let url = URL(string: "https://www.reddit.com/user/\(username)/about.json") {
                do {
                    let data = try Data(contentsOf: url)
                    do {
                        let decodedUser = try JSONDecoder().decode(user.self, from: data)
                        return decodedUser
                    } catch {
                        print(error)
                    }
                } catch {
                    print(error)
                }
            }
            didAppear = true
        }
        return getNilUser()
    }
}

我对此很陌生，所以如果我犯了一个愚蠢的错误，我很抱歉

I’m very new to this so if I made a stupid mistake I’m sorry

推荐答案

你不能得到这样的 JSON 数据.您必须使用 URLSession 类执行 HTTP 请求以便获取数据并对其进行解析.

You can't get JSON data like that. You have to execute a HTTP request using the URLSession class in order to get the data and parse it.

let username = "markregg"
let url = URL(string: "https://www.reddit.com/user/\(username)/about.json")!

URLSession.shared.dataTask(with: url) { data, response, error in
    if let error = error {
        print(error)
    } else if let data = data {
        do {
            let decodedUser = try JSONDecoder().decode(User.self, from: data)

        } catch {
            print(error)
        }
    } else {
        print("Request failed")
    }
}.resume()

另一件需要注意的事情是 URLSession 方法是异步的.简单来说，这意味着它们需要一些时间来执行并返回结果.因此，您不能使用像 return decodedUser 这样的简单返回语句来立即获得结果.研究如何使用 URLSession 更多.

Another thing to note is that URLSession methods are asynchronous. In simple terms it means they take some time to execute and return the result. So you can't use a simple return statement like return decodedUser to get the result right away. Look into how to use URLSession more.

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