使用 Core Data 时如何覆盖属性上的 getter？

Question

I want to be able to override the getter on a string property on one of my core data models and inside the getter I need to find out what the value is for that property.

@interface LabTest : NSManagedObject {
}
@property (nonatomic, retain) NSString *status;
@end

@implementation LabTest

@dynamic status;

- (NSString *)status {
    NSString *tempStatus = [super valueForKey:@"status"];
    //do some checking here
    return tempStatus;
}

@end

The code above crashes the process. I have tried a few different things, but I think they all end up in an infinite loop with the program crashing with a code of 139.

What is the correct way to access a core data member in the getter like this?

Answer 1

你有没有试过[self primitiveValueForKey:@"status"]而不是[super valueForkey:@"status"] ？

Answer 2

Just in case anyone is looking for a little more info on how to override getter methods and landed on this page...

Inside of your property definition you can specify getter and setter methods as follows:

@property (nonatomic, retain, getter = getterMethodName, setter = setterMethodName) NSString *someString;

You can specify the getter only, the setter only, or both.

Answer 3

The managed object creator in x-code has a checkbox that is normally unchecked just for this purpose.

Validation Methods http://www.nwcode.com/img/ValidationMethods.png

Answer 4

There's a really handy Xcode Snippets menu (Xcode 12 has a + button in the top right) that has great snippets for overriding lots of common Core Data code, including KVO-compliant accessors for object-types (getters + setters).