SwiftUI中JSONDecoder解码始终返回nil问题求助

我开发了一个SwiftUI应用，为测试需求创建了Mock仓库，从本地JSON文件获取数据而非调用API，但JSONDecoder的解码结果始终为nil。

本地JSON内容（存储于项目根目录）：

[    
    {        
        "ts": 1000000,        
        "id": 1,        
        "userName": "honeybee",        
        "userLocation": "Honey bee",        
        "userImageUrl": "user_1",        
        "title": "Here",        
        "postType": "post",        
        "postImageUrl": "food_1",    },    
    {        
        "ts": 1000000,        
        "id": 2,        
        "userName": "honeybee",        
        "userLocation": "Honey bee",        
        "userImageUrl": "user_2",        
        "title": "Here",        
        "postType": "store",        
        "postImageUrl": "food_2"    
    },
]

FeedItemEntity模型代码：

enum PostType: String, Codable {    
    case Post =  "post"    
    case Store = "store"    
    case Restaurant = "restaurant"    
    case Review = "review"    
    case Recipe = "recipe"
}

struct FeedItemEntity: Codable {    
    var ts: Int    
    var userName: String    
    var userLocation: String    
    var userImageUrl: String    
    var title: String    
    var postImageUrl: String    
    var postType: PostType    
    var rating: Int
}

extension FeedItemEntity: Identifiable {    
    var id: UUID {        
        let id = UUID()        
        return id    
    }
}

Mock服务代码：

class MockedFeedService: FeedServiceProtocol {    
    static let shared = MockedFeedService()

    func getFeed() -> Future<[ios_foodloose_app.FeedItemEntity], Error> {        
        return Future<[FeedItemEntity], Error> { promise in            
            guard let url = Bundle(for: MockedFeedService.self).url(forResource: "basic-test-feed-response",withExtension: "json"),                  
                  let data = try? Data(contentsOf: url) else {                
                return promise(.failure(NSError(domain: "", code: 401, userInfo: [ NSLocalizedDescriptionKey: "Error"])))            
            }            
            let response = try? JSONDecoder().decode( [FeedItemEntity].self, from: data)            
            promise(.success(response!))        
        }    
    }    
}

• JSON语法错误
  第一个JSON对象的"postImageUrl": "food_1",末尾多了逗号，数组最后也存在多余逗号。JSON不允许尾逗号（trailing comma），这会直接导致解析失败。

• 模型字段不匹配
  FeedItemEntity里的rating是必填Int类型，但JSON中完全没有这个字段。解码时找不到对应值会抛出错误，try?会将错误转为nil。

• Identifiable扩展冗余
  你手动生成UUID作为id，但JSON本身包含id字段，模型却未声明该属性，既浪费资源也不符合数据对应逻辑。

• 错误处理缺失
  用try?直接忽略了解码错误，无法获取具体失败原因，导致无法快速定位问题。

修正后的代码示例 #

修正后的JSON #

[    
    {        
        "ts": 1000000,        
        "id": 1,        
        "userName": "honeybee",        
        "userLocation": "Honey bee",        
        "userImageUrl": "user_1",        
        "title": "Here",        
        "postType": "post",        
        "postImageUrl": "food_1"    
    },    
    {        
        "ts": 1000000,        
        "id": 2,        
        "userName": "honeybee",        
        "userLocation": "Honey bee",        
        "userImageUrl": "user_2",        
        "title": "Here",        
        "postType": "store",        
        "postImageUrl": "food_2"    
    }
]

修正后的FeedItemEntity #

enum PostType: String, Codable {    
    case post = "post"    
    case store = "store"    
    case restaurant = "restaurant"    
    case review = "review"    
    case recipe = "recipe"
}

struct FeedItemEntity: Codable, Identifiable {    
    let id: Int // 直接使用JSON中的id
    var ts: Int    
    var userName: String    
    var userLocation: String    
    var userImageUrl: String    
    var title: String    
    var postImageUrl: String    
    var postType: PostType    
    var rating: Int? // 改为可选类型，适配JSON无该字段的情况
}

修正后的Mock服务（添加错误处理） #

class MockedFeedService: FeedServiceProtocol {    
    static let shared = MockedFeedService()

    func getFeed() -> Future<[FeedItemEntity], Error> {        
        return Future<[FeedItemEntity], Error> { promise in            
            guard let url = Bundle(for: MockedFeedService.self).url(forResource: "basic-test-feed-response",withExtension: "json"),                  
                  let data = try? Data(contentsOf: url) else {                
                return promise(.failure(NSError(domain: "MockService", code: 401, userInfo: [NSLocalizedDescriptionKey: "无法加载JSON文件"])))            
            }            
            do {
                let response = try JSONDecoder().decode([FeedItemEntity].self, from: data)
                promise(.success(response))
            } catch {
                print("解码错误：\(error)") // 打印错误便于调试
                promise(.failure(error))
            }
        }    
    }    
}

内容的提问来源于stack exchange，提问作者Seb