Swift 4-无法使用类型为((Codable)'的参数列表调用'encode' [英] Swift 4 - Cannot invoke 'encode' with an argument list of type '(Codable)'

问题描述

我构建了一组API函数，这些函数对对象进行编码(使用符合Codable的Struct)，然后将生成的JSON Data对象发布到服务器，然后对JSON响应进行解码.一切正常-尤其是对Swift 4.2中用于JSON解析的新方法感到满意.但是，现在我想重构代码，以便可以将代码重用于各种方法调用-当我这样做时，我会得到一个非常烦人的错误.

I have built a set of API functions which encode an object (using a Struct which conforms to Codable), then Posts the resulting JSON Data object to a server, then decodes the JSON response. All works fine - especially happy with the new method for JSON parsing in Swift 4.2. However, now I want to refactor the code so that I can reuse the code for various method calls - when I do I get a really annoying error.

func encodeRequestJSON(apiRequestObject: Codable) -> Data {
    do {
        let encoder = JSONEncoder()
        let jsonData = try encoder.encode(apiRequestObject)
        let jsonString = String(data: jsonData, encoding: .utf8)
        print(jsonString)
    } catch {
        print("Unexpected error")
        }
    return jsonData!
}

这是错误消息:

Cannot invoke 'encode' with an argument list of type '(Codable)'

我尝试将类型从Codable更改为Encodable，但除消息中的类型为(Encodable)以外，都收到相同的错误.有什么建议吗?我的后备方法是在当前ViewController中对数据进行编码，然后调用HTTPPost函数，然后在VC中进行解码.但这确实很笨拙.

I have tried changing the type from Codable, to Encodable but get the same error, except with type (Encodable) in the message. Any advice? My fall-back is to encode the data in the current ViewController, then call the HTTPPost function and then decode back in the VC. But that's really clunky.

推荐答案

您需要将具体类型传递给JSONEncoder.encode，因此您需要在Encodable(Codable不需要，因为它太严格了.)

You need a concrete type to be passed into JSONEncoder.encode, so you need to make your function generic with a type constraint on Encodable (Codable is not needed, its too restrictive).

func encodeRequestJSON<T:Encodable>(apiRequestObject: T) throws -> Data {
    return try JSONEncoder().encode(apiRequestObject)
}

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