从初始值设定项返回之前，不会在所有路径上调用'self.init'

Question

我正在使用Decodeable进行CoreData和JSON解析，在初始化器的末尾遇到一个错误，说'self.init' isn't called on all paths before returning from initializer:

import Foundation
import CoreData
extension CodingUserInfoKey {
static let managedObjectContext = CodingUserInfoKey(rawValue: "managedObjectContext")!
}
@objc(Task)
public class Task: NSManagedObject, Decodable {

enum CodingKeys: String, CodingKey {
case diff, title, desc, doc
}

required convenience public init(from decoder: Decoder) throws {
guard let context = decoder.userInfo[CodingUserInfoKey.managedObjectContext] as? NSManagedObjectContext else {
print("Decode context error")
return
}
guard let entity = NSEntityDescription.entity(forEntityName: "Task", in: context) else {
print("Decode entity error")
return
}
self.init(entity: entity, insertInto: context)
do {
let container = try decoder.container(keyedBy: CodingKeys.self)
self.diff = try container.decode(String.self, forKey: .diff)
self.title = try container.decode(String.self, forKey: .title)
self.desc = try container.decode(String.self, forKey: .desc)
self.doc = try container.decode(String.self, forKey: .doc)
} catch {
print("Decode key error")
}
}

}

我是不是错过了什么？

Answer 1

您可能应该在guard语句中抛出一个自定义错误，而不是仅仅返回。此外，您应该从解码器函数调用中删除do-catch：

enum ManagedObjectError: Error {
case decodeContextError
case decodeEntityError
}
required convenience public init(from decoder: Decoder) throws {
guard let context = decoder.userInfo[CodingUserInfoKey.managedObjectContext] as? NSManagedObjectContext else {
throw ManagedObjectError.decodeContextError
}
guard let entity = NSEntityDescription.entity(forEntityName: "Task", in: context) else {
throw ManagedObjectError.decodeEntityError
}
self.init(entity: entity, insertInto: context)

let container = try decoder.container(keyedBy: CodingKeys.self)
self.diff = try container.decode(String.self, forKey: .diff)
self.title = try container.decode(String.self, forKey: .title)
self.desc = try container.decode(String.self, forKey: .desc)
self.doc = try container.decode(String.self, forKey: .doc)
}

Answer 2

正如它所指出的，您还没有在所有路径上调用self.init。例如，如果context为nil，则返回时不调用self.init。

如果你想在不创建实例的情况下退出这个初始值设定项，你需要抛出一个错误，而不仅仅是返回。

由于这个init抛出，捕获错误然后丢弃它们也是没有意义的。让他们扔给打电话的人。