NSManagedObject类别和委托 [英] NSManagedObject with Category and Delegate

问题描述

我创建了一个名为MapState的 NSManagedObject 。然后我创建了一个类别来调用一些方法并存储一些额外的变量。

I created a NSManagedObject called MapState. I then created a category for it to call some methods and store some extra variables.

.h
#importMapStateDB.h

.h #import "MapStateDB.h"

@protocol MapStateDelegate;

@interface MapStateDB (MapState)

@property (weak, nonatomic) id <MapStateDelegate> delegate;

-(void)selectedSceneObject:(SceneObject *)sceneObject;
-(void)removeDisplayedScene;

@end


@protocol MapStateDelegate <NSObject>

-(void)displayScene:(SceneDB *)scene inState:(NSString *)state;
-(void)removeScene:(SceneDB *)scene;

@end

在.m：

@dynamic delegate;

-(void)setDelegate:(id<MapStateDelegate>)delegate {

}

如何做设置器？通常只是：

How do I do the setter? Normally it would just be:

-(void)setDelegate:(id<MapStateDelegate>)delegate {
    _delegate = delegate;
}

但是因为变量 @dynamic 而不是 @synthesize ，不会创建 _delegate 。 @synthesize 会产生错误。

But since the variable is @dynamic instead of @synthesize, no _delegate is created. And @synthesize creates an error.

我应该如何处理？

推荐答案

使用 @dynamic 意味着将在运行时创建适当的访问器。 NSManagedObject 对数据模型中的实体的属性执行此操作，但不对您声明的属性执行此操作。您可以可以使用一些ObjC运行时语法（这些API都存在，并且是受支持的，因此它不是可以被称为黑客的），但它不是微不足道的。 （如果 delegate 是实体上的临时属性，则使用 @dynamic 会很好，但这意味着代理必须是Core Data支持的类型之一，而不是任何实现协议的类）。

Using @dynamic implies that the appropriate accessors will be created at run time. NSManagedObject does that for attributes of entities in the data model, but not for properties you declare. You could do this with some ObjC runtime wizardry (the APIs all exist, and are supported, so it's not what might be called a hack) but it's not trivial. (Using @dynamic would be fine if delegate were a transient property on the entity, but that would mean that the delegate would have to be one of the types supported by Core Data instead of any class implementing the protocol).

但是有希望！如果你使用Xcode 7+生成 NSManagedObject 子类，可以在子类中添加自己的属性，而不用担心它们被覆盖。您可以通过添加 @synthesize 为委托工作，然后不添加自己的安装程序。

But there's hope! If you're using Xcode 7+ to generate NSManagedObject subclasses, it's safe to add your own properties in the subclass without fear of them being overwritten. You'd make the delegate property work by adding a @synthesize for it and then not adding your own setter. You don't have to provide one unless you need to do more than just set the property value.

如果您请需要一个自定义安装程序，修改 @synthesize 为

If you do need a custom setter, modify the @synthesize to be something like

@synthesize delegate = _delegate;

（您不必使用 _delegate 这里，任何有效的名称都很好）

(you don't have to use _delegate here, any valid name is fine)

然后添加一个setter，就像你的问题中分配给合成名称的那样。

Then add a setter like the one in your question that assigns to the synthesized name.

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