RealmSwift初始值设定项:在super.init调用之前自行使用 [英] RealmSwift initializer: self used before super.init call

问题描述

import RealmSwift
import Realm

public class Card : Object {
    var username : String
    var firstName : String
    var lastName : String


    init?(dictionary: [String:Any]?) {
        guard let dictionary = dictionary , let username = dictionary["username"] as? String else { return else}

        self.username = username
        self.firstName = firstName 
        self.lastName = lastName
    }

    required public init() {
        fatalError("init() has not been implemented")
    }

    required public init( realm: RLMRealm, schema: RLMObjectSchema) {
        fatalError("init(realm:schema:) has not been implemented")
    }

    required public init( value: Any, schema: RLMSchema) {
       fatalError("init(value:schema:) has not been implemented")
    }
}

我得到:

在super.init调用之前使用

'self'

'self' used before super.init call

我的课堂正常工作.添加RealmSwift之后，我遇到了这些错误.如果我添加super.init()它会抱怨:

I had my class working properly. After adding RealmSwift i'm getting those errors. If I add super.init() it complains:

未在super.init调用中初始化属性'self.username'

Property 'self.username' not initialized at super.init call

推荐答案

这里发生了几件事.

首先，当添加自定义初始化程序时对于Object 的子类，必须将它们声明为便捷初始化程序.不可能从子类中正确实现Object所需的初始化程序，而使用便捷的初始化程序将消除尝试执行此操作的需要.这也意味着您将改为从自定义初始化程序中将其委托给self.init()而不是super.init().

First and foremost, when adding custom initializers to subclasses of Object, they must be declared as convenience initializers. It's not possible to correctly implement Object's required initializer from a subclass, and using a convenience initializer removes the need to try and do this. It also means you'll instead delegate to self.init() rather than super.init() from within your custom initializer.

第二，存储的属性必须具有初始值.如果没有初始值，Swift编译器将不会为您的类合成初始化程序(在这种情况下，是调用基类的init()版本).

Secondly, stored properties must have an initial value. Without the initial value the Swift compiler will not synthesize initializers for your class (in this case, a version of init() that calls through to the base class).

最后，正如我在其他地方提到的那样，必须使用Swift的dynamic修饰符声明类型String的属性，以允许Realm截获对它们的获取/设置操作.

Finally, as I mentioned elsewhere, properties of type String must be declared using Swift's dynamic modifier to allow Realm to intercept get / set operations on them.

通过遵循这些准则，您将得到如下结果:

By following these guidelines you'll end up with something like so:

public class Card : Object {
    dynamic var username: String = ""
    dynamic var firstName: String = ""
    dynamic var lastName: String = ""

    convenience init?(dictionary: [String:Any]?) {
        guard let dictionary = dictionary,
            let username = dictionary["username"] as? String,
            let firstName = dictionary["firstName"] as? String,
            let lastName = dictionary["lastName"] as? String
            else { return nil }

        self.init()

        self.username = username
        self.firstName = firstName
        self.lastName = lastName
    }
}

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