ios - 如何使 Swift Codable 类型更加通用

Question

我目前正在使用处理公交车预测的 API。为某个站点的预测返回的 JSON 有一个有趣的怪癖。当有多个停止预测时，JSON 看起来像这样:

...
"direction": {
            "prediction": [
                {
                    "affectedByLayover": "true",
                    "block": "241",
                    "dirTag": "loop",
                    "epochTime": "1571785998536",
                    "isDeparture": "false",
                    "minutes": "20",
                    "seconds": "1208",
                    "tripTag": "121",
                    "vehicle": "1698"
                },
                {
                    "affectedByLayover": "true",
                    "block": "241",
                    "dirTag": "loop",
                    "epochTime": "1571787798536",
                    "isDeparture": "false",
                    "minutes": "50",
                    "seconds": "3008",
                    "tripTag": "122",
                    "vehicle": "1698"
                },
                {
                    "affectedByLayover": "true",
                    "block": "241",
                    "dirTag": "loop",
                    "epochTime": "1571789598536",
                    "isDeparture": "false",
                    "minutes": "80",
                    "seconds": "4808",
                    "tripTag": "123",
                    "vehicle": "1698"
                }
            ],
            "title": "Loop"
        }
...

但是，当只有一个停止预测时，JSON 看起来像这样:

...
"direction": {
            "prediction": 
                {
                    "affectedByLayover": "true",
                    "block": "241",
                    "dirTag": "loop",
                    "epochTime": "1571785998536",
                    "isDeparture": "false",
                    "minutes": "20",
                    "seconds": "1208",
                    "tripTag": "121",
                    "vehicle": "1698"
                }
            "title": "Loop"
        }
...

请注意，“预测”不再位于数组内——这是我认为使用 Swift Codable 类型解码 JSON 时事情变得复杂的地方。对于“方向”和“预测”，我的模型看起来像这样

struct BTDirection: Codable {
    let title: String!
    let stopTitle: String!
    let prediction: [BTPrediction]!
}

struct BTPrediction: Codable {
    let minutes: String!
    let vehicle: String!
}

基本上发生的事情是 BTDirection 中的 prediction 正在寻找一个 BTPrediction 数组，但是在上面的第二种情况下，这不是一个数组，因此解码失败。如何使我的模型更灵活以适应数组或单个对象？理想情况下，在第二种情况下，prediction 仍然是单个 BTDirection 的数组。对此的任何帮助将不胜感激。

Answer 1

你可以试试

struct BTDirection:Codable {

    let title,stopTitle: String
    let prediction: [BTPrediction]

    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        title = try container.decode(String.self, forKey: .title)
        stopTitle = try container.decode(String.self, forKey: .stopTitle)
        do {
            let res = try container.decode([BTPrediction].self, forKey: .prediction)
            prediction = res
        }
        catch { 
              let res = try container.decode(BTPrediction.self, forKey: .prediction)
              prediction = [res] 
        }  
    }
}