如何从 Codable 结构中捕获 init（来自解码器：解码器）中的错误？

Posted 2023-02-24

【中文标题】如何从 Codable 结构中捕获 init（来自解码器：解码器）中的错误？

【英文标题】：How to do-catch error in init(from decoder:Decoder) from a Codable struct?

【发布时间】：2018-05-18 04:36:17

【问题描述】：

let jsonString = """
                    
                        "name":1,
                        "gender":"male",
                    
                    """

struct Person: Codable 
    var name: String
    var gender: String

    public init(from decoder: Decoder) throws 
        do 
            let container = try decoder.container(keyedBy: CodingKeys.self)
            name = try container.decode(String.self, forKey: .name)
            gender = try container.decode(String.self, forKey: .gender)
         catch 
            print("XXXXXX \(error)")
        
    

从上面的代码来看，它不会编译，因为它会报错，

从初始化程序返回而不初始化所有存储的属性。

我想抛出一些错误，但是如果没有，我该怎么做，

为每个属性设置默认值。 将它们全部设为可选。

【问题讨论】：

请注意，对于此数据结构，自定义初始化程序是多余的。

【参考方案1】：

您不需要init(from decoder: Decoder) 中的do-catch，因为它已经标记为throws。所以就这样做吧：

public init(from decoder: Decoder) throws 
    let container = try decoder.container(keyedBy: CodingKeys.self)
    name = try container.decode(String.self, forKey: .name)
    gender = try container.decode(String.self, forKey: .gender)

解码可以使用do-catch 来查看上述init(from:) 方法中抛出的任何异常，如下例所示：

struct Person: Codable 
    var name: String
    var gender: String

    // Note: This is not a very good example because this init method
    // is not even necessary in this case, since the automatically-
    // synthesized `init(from:)` method does exactly the same thing. I've
    // left it here to illustrate that you don't need to have a `do-catch`
    // in this method and can instead just use `try`, since the method
    // is marked as `throws`.
    public init(from decoder: Decoder) throws 
        let container = try decoder.container(keyedBy: CodingKeys.self)
        name = try container.decode(String.self, forKey: .name)
        gender = try container.decode(String.self, forKey: .gender)
    


class PersonDecoder 
    func person(decodedFrom data: Data) -> Person? 
        do 
            // The `JSONDecoder.decode(_:from:)` method calls
            // `Person.init(from:)`, which can throw, which is why
            // `JSONDecoder.decode(_:from:)` also throws.
            let person = try JSONDecoder().decode(Person.self, from: data)
            return person
         catch 
            // Inspect any thrown errors here.
            print(error)

            return nil
        
    


let personData = Data("""

    "name": 1,
    "gender": "male"

""".utf8)

let personDecoder = PersonDecoder()

// Prints: "The data couldn’t be read because it isn’t in the correct format."
// and `person` is nil.
let person = personDecoder.person(decodedFrom: personData)

【讨论】：

那么如何知道异常呢？

@Nuibb 如果您在调用周围使用do-catch 来解码数据，则无论解码是什么都可以被告知异常。我将在我的答案中添加一个示例。

@TylerTheCompiler 它没有去捕捉范围。

@TylerTheCompiler 好的，它确实成功了。但是需要编辑 Swift Error 断点才能继续，而不是卡在那里。

@hasan 我不确定你在说什么。