json - 崩溃 : Convert dictionary to Json string in Swift 3

Question

我正在尝试将我的 swift 字典转换为 Json 字符串，但说奇怪的崩溃

由于未捕获的异常“NSInvalidArgumentException”而终止应用程序，原因:“JSON 写入中的无效类型 (_SwiftValue)”

我的代码:

let jsonObject: [String: AnyObject] = [
            "firstname": "aaa",
            "lastname": "sss",
            "email": "my_email",
            "nickname": "ddd",
            "password": "123",
            "username": "qqq"
            ]

do {
    let jsonData = try JSONSerialization.data(withJSONObject: jsonObject, options: .prettyPrinted)
    // here "jsonData" is the dictionary encoded in JSON data

    let decoded = try JSONSerialization.jsonObject(with: jsonData, options: [])
    // here "decoded" is of type `Any`, decoded from JSON data

    // you can now cast it with the right type
    if let dictFromJSON = decoded as? [String:String] {
        // use dictFromJSON
    }
} catch {
    print(error.localizedDescription)
}

请帮我!

问候。

Answer 1

字符串 不是类型 AnyObject .对象是引用类型，但 字符串 在 swift 中具有值语义。 A 字符串 但是，可以是 类型任意 ，所以下面的代码有效。我建议你阅读 Swift 中的引用类型和值语义类型；这是一个微妙但重要的区别，它也不同于您对大多数其他语言的期望，其中 String 通常是一种引用类型(包括 objective-c )。

    let jsonObject: [String: Any] = [
        "firstname": "aaa",
        "lastname": "sss",
        "email": "my_email",
        "nickname": "ddd",
        "password": "123",
        "username": "qqq"
    ]

    do {
        let jsonData = try JSONSerialization.data(withJSONObject: jsonObject, options: .prettyPrinted)
        // here "jsonData" is the dictionary encoded in JSON data

        let decoded = try JSONSerialization.jsonObject(with: jsonData, options: [])
        // here "decoded" is of type `Any`, decoded from JSON data

        // you can now cast it with the right type
        if let dictFromJSON = decoded as? [String:String] {
            print(dictFromJSON)
        }
    } catch {
        print(error.localizedDescription)
    }