Question

Does anyone know if there is a way to set a property like a string in the User Defined Runtime Atributes sections of Interface Builder without creating a subclass of said component? For example, I want to store a metadata value for each component in my interface that I use later. I just don’t want to have to create a subclass or each component to add a metadata property.

This is one approach I came up with. Opinions?

#import <UIKit/UIKit.h>
#import <objc/runtime.h>


@interface UIControl(MetaData)

@property (nonatomic, retain) id entityProperty;

@end

@implementation  UIControl(MetaData)

static char const * const EntityPropertyKey = "EntityProperty";

@dynamic entityProperty;

- (id)entityProperty {
    return objc_getAssociatedObject(self, EntityPropertyKey);
}

- (void)setEntityProperty:(id)newEntityProperty {
    objc_setAssociatedObject(self, EntityPropertyKey, newEntityProperty,     OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}


@end

…

if (textField.entityProperty) 
     [managedObject setValue: textField.text forKey:textField.entityProperty];

Answer 1

You could keep an NSDictionary somewhere, perhaps in a singleton object that has methods for issuing unique ids for objects and storing metadata by the id keys in the dictionary. The UI objects have a tag property that you can use, if your ids are just incremented integers. Then the dictionary keys would just be NSNumbers for those unique integers.

Like this:

#import <Foundation/Foundation.h>

@interface ACLMetadataManager : NSArray

+(ACLMetadataManager*) sharedMetadataManager;
-(NSUInteger) getUniqueId;
-(void) setObject: (id) object forId:(NSUInteger) theId;
-(id) objectForId:(NSUInteger) theId;

@end

And:

#import "ACLMetadataManager.h"
@implementation ACLMetadataManager { // Private variables
    NSMutableDictionary *_metadata;
    NSUInteger _ids;
}

- (id)init {
    self = [super init];
    if (self) {
        _metadata = [[NSMutableDictionary alloc] init];
    }
    return self;
}

+(ACLMetadataManager*) sharedMetadataManager { // Singleton getter
    static ACLMetadataManager *instance;
    if (instance != nil) {
        return instance;
    }
#if __IPHONE_OS_VERSION_MAX_ALLOWED >= __IPHONE_4_0
    static dispatch_once_t oneTimeThread;
    dispatch_once(&oneTimeThread, ^(void) {
        instance = [[ACLMetadataManager alloc] init];
    });
#else
    @synchronized(self) {
        instance = [[ACLMetadataManager alloc] init];
    }
#endif
    return instance;
}

-(NSUInteger) getUniqueId { // Increment unique id when getter is called.
    return ++_ids; // Start from 1 because tag is 0 by default.
}

-(void) setObject: (id) object forId:(NSUInteger) theId {
    [_metadata setObject:object forKey:[NSNumber numberWithInteger:theId]];
}

-(id) objectForId:(NSUInteger) theId {
    return [_metadata objectForKey:[NSNumber numberWithInteger:theId]];
}

// Override some methods to ensure singleton stays instantiated.
- (id) retain {
    return self;
}
- (oneway void) release {
    // Does nothing here.
}
- (id) autorelease {
    return self;
}
- (NSUInteger) retainCount {
    return INT32_MAX;
}
@end

Usage:

ACLMetadataManager *metadataManager = [ACLMetadataManager sharedMetadataManager];
myControl.tag = [metadataManager getUniqueId];
[metadataManager setObject:myMetadata forId:myControl.tag];