无法将类型"Codable"(也称为"Decodable& Encodable")的值转换为预期的参数类型"T.Type"
我正在处理一个处理JSON解析的小型结构.到目前为止,一切正常,除了我要传递自定义结构作为要在 JSONDecoder().decode(type.self,from:data)
的解码中使用的结构之外,但这是抛出以下错误:
I'm working on a small struct that handles the parsing of JSON. Up until now it is all working except I am wanting to pass a custom struct as a structure to use on the decode in JSONDecoder().decode(type.self, from: data)
but this is throwing the following error:
无法将类型"Codable"(也称为"Decodable& Encodable")的值转换为预期的参数类型"T.Type"
Cannot convert value of type 'Codable' (aka 'Decodable & Encodable') to expected argument type 'T.Type'
private func parseJson(data: Data, type: Codable) -> Codable? {
do {
let decoded = try JSONDecoder().decode(type.self, from: data)
return decoded
} catch {
print("JSON decode error: \(error.localizedDescription)")
}
return nil
}
是否可以将结构体传递给此方法以用作 decode()
函数的类型?如果我直接设置要传递给该函数的类型,则该代码将按预期工作,仅当我尝试将其传递时才会出错.
Is there a way that I can pass a struct into this method to use as the type for the decode()
function? If I directly set the type I'm trying to pass into the function on the decode() function the code works as expected, it only errors out when I attempt to pass it in.
您需要的是通用方法:
private func parseJson<T: Decodable>(data: Data, type: T.Type) -> T? {
do {
return try JSONDecoder().decode(type.self, from: data)
} catch {
print("JSON decode error:", error)
return nil
}
}
您还可以省略类型并显式设置结果对象的类型:
You can also omit the type and explicitly set the type of the resulting object:
private func parseJson<T: Decodable>(data: Data) -> T? {
do {
return try JSONDecoder().decode(T.self, from: data)
} catch {
print("JSON decode error:", error)
return nil
}
}
游乐场测试:
Playground testing:
struct User: Codable {
let id: Int
let name: String
}
let user: User = .init(id: 2, name: "abc")
let userData = try! JSONEncoder().encode(user)
let decodedUser: User = parseJson(data: userData)!
decodedUser.name // "abc"
注意:我返回的是可选类型,但绝对应该使方法抛出并返回非可选的类型,如下面在我扩展数据的地方所见:
Note: I am returning optional types but you should definitely make your methods throw and return a non optional as you can see below where I am extending Data:
extension Data {
func decodedObject<T: Decodable>() throws -> T {
try JSONDecoder().decode(T.self, from: self)
}
}
do {
let decodedUser: User = try userData.decodedObject()
print(decodedUser.name) // "abc"
} catch {
print(error)
}