ios - List of class properties in Objective-C

Question

Is there a way to get an array of class properties of certain kind? For example if i have interface like this

@interface MyClass : NSObject
    @property (strong,nonatomic) UILabel *firstLabel;
    @property (strong,nonatomic) UILabel *secondLabel;        
@end

can i get the reference to those labels in implementation without knowing their name?

@implementation MyClass
    -(NSArray*)getListOfAllLabels
    {
            ?????
    }        
@end

I know i can do it easily with [NSArray arrayWithObjects:firstLabel,secondLabel,nil], but i would like to do it with some kind of class enumeration like for (UILabel* oneLabel in ???[self objects]???)

Answer 1

So more precisely, you want dynamic, runtime observaion of the properties, if I got it correctly. Do something like this (implement this method on self, the class you want to introspect):

#import <objc/runtime.h>

- (NSArray *)allPropertyNames
{
    unsigned count;
    objc_property_t *properties = class_copyPropertyList([self class], &count);

    NSMutableArray *rv = [NSMutableArray array];

    unsigned i;
    for (i = 0; i < count; i++)
    {
        objc_property_t property = properties[i];
        NSString *name = [NSString stringWithUTF8String:property_getName(property)];
        [rv addObject:name];
    }

    free(properties);

    return rv;
}

- (void *)pointerOfIvarForPropertyNamed:(NSString *)name
{
    objc_property_t property = class_getProperty([self class], [name UTF8String]);

    const char *attr = property_getAttributes(property);
    const char *ivarName = strchr(attr, 'V') + 1;

    Ivar ivar = object_getInstanceVariable(self, ivarName, NULL);

    return (char *)self + ivar_getOffset(ivar);
}

Use it like this:

SomeType myProperty;
NSArray *properties = [self allPropertyNames];
NSString *firstPropertyName = [properties objectAtIndex:0];
void *propertyIvarAddress = [self getPointerOfIvarForPropertyNamed:firstPropertyName];
myProperty = *(SomeType *)propertyIvarAddress;

// Simpler alternative using KVC:
myProperty = [self valueForKey:firstPropertyName];

Hope this helps.