ios - 如何在 Swift 中为 NSManagedObject 子类指定初始化器？

Question

class Alternative: NSManagedObject {

    @NSManaged var text: String
    @NSManaged var isCorrect: Bool
    @NSManaged var image: NSData
} 

convenience init(text: String, isCorrect: Bool, entity: NSEntityDescription, insertIntoManagedObjectContext context: NSManagedObjectContext!) {
        let alternative = Alternative(entity: entity, insertIntoManagedObjectContext: context) as Alternative
        alternative.text = text
        alternative.isCorrect = isCorrect
        return alternative
}

我想创建一个方法，让我可以通过这个调用来初始化新对象:

let newAlternative = Alternative("third platform", True, entityDescription, managedObjectContext)

但是我得到了错误:

Convenience initializer for Alternative must delegate with self.init

我需要在我的初始化程序中更改什么才能使我的示例用法正常工作？

Answer 1

便捷初始化器必须在self 上调用指定的初始化器:

convenience init(text: String, isCorrect: Bool, entity: NSEntityDescription, insertIntoManagedObjectContext context: NSManagedObjectContext!) {
    self.init(entity: entity, insertIntoManagedObjectContext: context)
    self.text = text
    self.isCorrect = isCorrect
}

这将被称为

let newAlternative = Alternative(text: "third platform", isCorrect: true,
     entity: entityDescription, insertIntoManagedObjectContext: managedObjectContext)

此外，您还可以将实体描述的创建移动到便利初始值设定项中，而不是将其作为参数传递(由Mundi 的回答):

convenience init(text: String, isCorrect: Bool, insertIntoManagedObjectContext context: NSManagedObjectContext!) {
    let entity = NSEntityDescription.entityForName("Alternative", inManagedObjectContext: context)!
    self.init(entity: entity, insertIntoManagedObjectContext: context)
    self.text = text
    self.isCorrect = isCorrect
}