从初始化程序返回之前，并非在所有路径上都调用'self.init'

问题描述

我正在this之后使用Decodable处理CoreData和JSON解析，并且在初始化器的末尾说'self.init' isn't called on all paths before returning from initializer时遇到错误：

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")
        }
    }
    
}

我想念什么吗？

解决方法

如前所述，您并未在所有路径上都调用self.init。例如，如果context为nil，则返回时不调用self.init。

如果要退出此初始化程序而不创建实例，则需要抛出错误，而不仅仅是返回。

由于此init引发，因此捕捉错误然后丢弃错误也没有意义。只是让他们扔给呼叫者。

,

您可能应该在guard语句中引发自定义错误，而不仅仅是返回。另外，您还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)
}