Question

Shortly: how to determine if id is CFType or not at runtime

i’m implementing dynamic core data attributes and in willSave method of ExtendedManagedObject i wanna check if the id value is CFType to store it into plist file.

If I’m trying to save to plist UIImage, that is not toll-free bridged with CF (apple docs), I am getting an error:

2011-11-17 17:16:25.294 [490:707] Error saving extended data: Property list invalid for format (property lists cannot contain objects of type ‘CFType’)

Can I check it with some method or I have to implement by myself (just isKindOfClass from docs)?

I don’t want to implement accessors in NSManagedObject subclass, I dont know exactly how many urls I’ll get from entities properties. Question is about dynamic extended attributes at runtime.

- (void)willSave
{
NSDictionary *changes = [self valueForKey:@"extendedChanges"];
if (changes!=nil) {
    // merge changes into snapshot
    NSMutableDictionary *dict = [[self extendedSnapshot] mutableCopy];
    NSEnumerator *e = [changes keyEnumerator];
    NSString *key;
    while (key=[e nextObject]) {
        id value = [changes objectForKey:key];



        if (value==[NSNull null])
            [dict removeObjectForKey:key];
        else if (#ugly and I'm not shure is thread safe **else if ([value isKindOfClass:[NSArray class]] || [value isKindOfClass:[NSDictionary class]] || [value isKindOfClass:[NSDate class]] || [value isKindOfClass:[NSData class]] || [value isKindOfClass:[NSString class]] || [value isKindOfClass:[NSNumber class]])**)
            [dict setObject:value forKey:key];
    }

    // archive as binary plist
    NSData *data = nil;
    if ([dict count]>0) {
        NSString *error=nil;
        data = [NSPropertyListSerialization dataFromPropertyList:dict 
                                                          format:NSPropertyListBinaryFormat_v1_0 errorDescription:&error];
        if (error!=nil) {
            NSLog(@"Error saving extended data: %@", error);
            [error release];
        }
    }
    [dict release];
    [self setPrimitiveValue:data forKey:@"extendedData"];
}
[super willSave];
}

Answer 1

That’s a wrong way to approach the problem. The blog post you referenced saves the extended attributes as a serialized plist. The plist can contain only the following types of objects, as written in the official doc:

NSArray, NSDictionary, NSDate, NSData, NSString and NSNumber.

Other classes are just not allowed. Don’t add objects of any other class to the attributes extended this way.

Also, saving an image file in a CoreData database is not a good idea, generally speaking, read On Blobs in the official doc. Instead, save the UIImage in a file and write the file path in the CoreData database.

---

If you just have a transient property which is not saved to the database, you don’t even have to go through the trouble of creating extended attributes. Just add it as a property of a subclass of NSManagedObject:

@interface MyManagedObject: NSManagedObject {
}
@property(retain, nonatomic) UIImage* thumbnail;
@property(retain, nonatomic) NSDictionary* thumbnailDictionary;
@end

without adding thumbnail in the CoreData model. Then do the corresponding @synthesize in the .m file. The property added this way to a managed object is just not saved.

If you want to keep unknown number of thumbnails, you can put an NSDictionary (or NSArray) containing UIImage*s.

---

If you really do want to get CFType from an NSObject*, do the following:

NSObject* x= ...;
CFTypeID typeID=CFGetTypeID((CFTypeRef)x);
if(typeID != CFStringGetTypeID() &&
   typeID != CFDateGetTypeID() &&
   typeID != CFDataGetTypeID() &&
   typeID != CFDictionaryGetTypeID() &&
   typeID != CFArrayGetTypeID()  ) {
       ... it's a non-plistable type ...
}

The ugly if clause is there because there’s no public function which gives you the CFTypeID of an un-bridged Objective-C object.
Read CFType reference. But I don’t recommend doing this.