将CLLocationCoordinate2D存储在CoreData中可转换

问题描述

我想在CoreData中存储一个CLLocationCoordinate2D对象.我在实体中创建了一个名为 location 的属性，其类型为 Transformable .我创建了一个NSManagedObject的子类，如下所示:

I want to store a CLLocationCoordinate2D Object in CoreData. I've created an attribute in my entity called location with type Transformable. I've created a subclass of NSManagedObject which looks like this:

extension Task {

    @nonobjc public class func fetchRequest() -> NSFetchRequest<Task> {
        return NSFetchRequest<Task>(entityName: "Task");
    }

    @NSManaged public var name: String?
    @NSManaged public var location: CLLocationCoordinate2D

}

但是当我想设置属性时会抛出错误

But when I want to set the attribute it throws an error

let task = Task(context: context)
task.name =  "Hello"
task.location = CLLocationCoordinate2D(latitude: CLLocationDegrees(10), longitude: CLLocationDegrees(12))

在此错误消息:

2016-12-24 11:50:27.425833 CoreDataTodo[839:273413] [error] error: Property 'setLocation:' is a scalar type on class 'Task' that does not match its Entity's property's scalar type.  Dynamically generated accessors do not support implicit type coercion.  Cannot generate a setter method for it.
CoreData: error: Property 'setLocation:' is a scalar type on class 'Task' that does not match its Entity's property's scalar type.  Dynamically generated accessors do not support implicit type coercion.  Cannot generate a setter method for it.
2016-12-24 11:50:27.426143 CoreDataTodo[839:273413] -[Task setLocation:]: unrecognized selector sent to instance 0x1766eca0
2016-12-24 11:50:27.426780 CoreDataTodo[839:273413] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[Task setLocation:]: unrecognized selector sent to instance 0x1766eca0'
*** First throw call stack:
(0x1c5a0df7 0x1b803077 0x1c5a6505 0x1c5a4579 0x1c4c93d8 0x4b8cc 0x4bd60 0x21681ee5 0x21681e73 0x2166bf97 0x2168179b 0x216812e7 0x2167bee7 0x2164ccf5 0x21de898d 0x21de25d3 0x1c55c71b 0x1c55c225 0x1c55a4fb 0x1c4a9533 0x1c4a9341 0x1dc80bfd 0x216b7e27 0x216b2551 0x4f520 0x1bc7350b)
libc++abi.dylib: terminating with uncaught exception of type NSException

推荐答案

要使用可转换属性，您需要以下条件之一:

To use a transformable attribute, you need one of the following:

• 符合 NSCoding 的属性类型. CLLocationCoordinate2D 不能，部分原因是只有类可以符合要求.这就是这些错误消息试图解释的内容.
• NSValueTransformer 的自定义子类，可以在数据类型和 NSData 之间进行转换.

• An Attribute type that conforms to NSCoding. CLLocationCoordinate2D does not, in part because only classes can conform. This is what those error messages are trying to explain.
• A custom subclass of NSValueTransformer that can convert between the data type and NSData.

您可以使用第二个选项.但是，将纬度和经度值分别存储为自己的属性会更容易.然后，将便利方法添加到您的子类中，将它们组合在一起并返回 CLLocationCoordinate2D .

You could use the second option. But it'd be easier to store the latitude and longitude values separately as their own attributes. Then add a convenience method to your subclass that combines them and returns a CLLocationCoordinate2D.

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