ios - 在可编码类中声明空字典

Question

我想像这样发送空字典

“visitor_attrs”: {}

我尝试在类中实现空字典。在解码器中我收到警告:

No 'decode' candidates produce the expected contextual result type 'Dictionary'

我该怎么做？

var data: String
var event: String
var visitorAttrs: Dictionary<String, Any>

init(data: String, event: String) {
    self.data = data
    self.event = event
    self.visitorAttrs = [:]
}

private enum CodingKeys: String, CodingKey {
    case data
    case event
    case visitorAttrs = "visitor_attrs"
}

required public init(from decoder: Decoder) throws {
    let container = try decoder.container(keyedBy: CodingKeys.self)
    self.data = try container.decode(String.self, forKey: .data)
    self.event = try container.decode(String.self, forKey: .event)
    self.visitorAttrs = try container.decode(Dictionary<String:Any>.self, forKey: .visitorAttrs)
}

public func encode(to encoder: Encoder) throws {
    var container = encoder.container(keyedBy: CodingKeys.self)
    try container.encode(self.data, forKey: .data)
    try container.encode(self.event, forKey: .event)
    try container.encode(self.visitorAttrs, forKey: .visitorAttrs)
} 

Answer 1

我的假设是，因为 visitorAttrs 在您的 JSON 响应中为空，所以无法从中获取字典，因为没有字典。

你有两个选择(据我所知)

1. 使 visitorAttrs 属性成为可选属性，这样即使您没有任何属性，它仍然能够正确解码，或者，

2. 如果解码失败，将 visitorAttrs 的值设置为空字典

let visitorAttrs = try? container.decode(Dictionary<String:Any>.self, forKey: .visitorAttrs)
self.visitorAttrs = visitorAttrs ?? [:]