How to store custom objects with struct in Coredata

Question

I have to store a custom class object to Coredata. The problem is my custom class contains structs,enum etc.I tried following method.

-(void)encodeWithCoder:(NSCoder *)encoder .

But am getting this error

[NSKeyedArchiver encodeValueOfObjCType:at:]: this archiver cannot encode structs'

What is the best practice to store this object to Coredata. Please help me.

Answer 1

With a struct, I think, it would be best to create a function that can encode and decode the struct, like any Objective-C object.

With enums, I am not so sure. Enums are just numbers associated with a name, so just enode and decode them as a numbers.

Answer 2

You can wrap the struct in a NSData, ie

To encode with archiver

[coder encodeObject:[NSData dataWithBytes:&my_struct length:sizeof(my_struct)] 
             forKey:@"my_struct"];

and to decode with archiver

NSData *data = [coder decodeObjectForKey:@"my_struct"];
[data getBytes:&my_struct length:sizeof(my_struct)];

Answer 3

You should have a custom implementation of the NSCoding protocol in your custom class. In your own implementations of -[initWithCoder:] and -[encodeWithCoder:], you can then encode/decode the struct objects in any way you please.

On way to do this would be to call [coder encodeObject:[NSValue valueWithBytes:&yourStructVariable objCType:@encode(struct YourStructName)] forKey:@"someKey"]; in -[encodeWithCoder:] and do the equivalent decoding in -[initWithCoder:].

You can then just store the class objects as transformable in Core Data.