How to set Custom Properties in iOS?

Question

I am using Core Data and would like to run some custom code when setting a property.

@interface FTRecord : NSManagedObject

@property (nonatomic) NSTimeInterval timestamp;


@implementation FTRecord

@dynamic timestamp;

-(void)setTimestamp:(NSTimeInterval)newTimestamp
{
    //run custom code....

    //and now how to pass the value to the actual property?
    [self setTimestamp:newTimestamp];
}

In this case I have defined the setter body for the timestamp property. But how do I set the value of the property without running into a recursion loop?

@MartinR I don't think that's the same question -- the one you found is about dependent properties, not simply writing your own setter. — Jesse Rusak, Oct 30 '13 at 20:04
@JesseRusak: You might be right, the questions are different, but the answers are the same (or at least very similar). — Martin R, Oct 30 '13 at 20:10

Jesse Rusak · Answer 1 · 2013-10-30T20:03:37.010

2

There's a magical accessor generated for each property, which in your case would be called setPrimitiveTimestamp: which you can use for this. Take a look at the docs for NSManagedObject's - (void)setPrimitiveValue:(id)value forKey:(NSString *)key.

So, you want:

-(void)setTimestamp:(NSTimeInterval)newTimestamp
{
    //run custom code....

    //and now how to pass the value to the actual property?
    [self willChangeValueForKey:@"timestamp"];
    [self setPrimitiveTimestamp:newTimestamp];
    [self didChangeValueForKey:@"timestamp"];
}

edited Oct 30 '13 at 20:03

answered Oct 30 '13 at 17:28

Jesse Rusak

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Jesse, thanks for this. This method is listed under `Methods you must NOT override` though. – Houman Oct 30 '13 at 17:34
Yes, that's correct. You need to override the `setTimestamp:` method, as you've done, and call `setPrimitiveTimestamp:` from there. – Jesse Rusak Oct 30 '13 at 17:56
I've updated my answer with an example, which I hope will clarify. – Jesse Rusak Oct 30 '13 at 17:57
And I've added the needed KVO stuff; I forgot NSManagedObject opts out of automatic notifications. – Jesse Rusak Oct 30 '13 at 20:04

How to set Custom Properties in iOS?

1 Answers1