Objective- C - Looping through all properties in a class?

Question

Is there a way to loop through all properties in an object and get their \"name\" and \"value\".

I am trying to write a category to serialize objects to a string, ba

Answer 1

I don't have comment privileges yet, but to add to @Costique's answer, there is an additional attribute Type value "V" which is the name of the IVar to which a property may be bound (via synthesize). This can be readily discovered with this

@interface Redacted : NSObject

@property (atomic, readonly) int foo;

@end

---

@implementation Redacted

@synthesize foo = fooBar;

@end

// for all properties
unsigned propertyCount = 0;
objc_property_t *properties = class_copyPropertyList([object class], &propertyCount);
for (int prop = 0; prop < propertyCount; prop++)
{
    // for all property attributes
    unsigned int attributeCount = 0;
    objc_property_attribute_t* attributes = property_copyAttributeList(property, &attributeCount);
    for (unsigned int  attr = 0; attr < attributeCount; attr++)
    {
        NSLog(@"Attribute %d: name: %s, value: %s", attr, attributes[attr].name, attributes[attr].value);
    }
}

---

2013-07-08 13:47:16.600 Redacted5162:303] Attribute 0: name: T, value: i

2013-07-08 13:47:16.601 Redacted[5162:303] Attribute 1: name: R, value:

2013-07-08 13:47:16.602 Redacted[5162:303] Attribute 2: name: V, value: fooBar

Answer 2

Maybe class_copyPropertyList() will do what you are after - but notice that it only returns declared properties.

Not all properties are declared - NSDictionary and NSMutableDictionary are examples of classes where you can set properties that are not declared in the class.

More in the docs.

Answer 3

You can use this code to enumerate all properties declared in a class, and all attributes of the properties. I guess you're more interested in parsing the type attribute. They are detailed here.

unsigned int numOfProperties;
objc_property_t *properties = class_copyPropertyList([self class], &numOfProperties);
for ( unsigned int pi = 0; pi < numOfProperties; pi++ ) {
    // Examine the property attributes
    unsigned int numOfAttributes;
    objc_property_attribute_t *propertyAttributes = property_copyAttributeList(properties[pi], &numOfAttributes);
    for ( unsigned int ai = 0; ai < numOfAttributes; ai++ ) {
        switch (propertyAttributes[ai].name[0]) {
            case 'T': // type
                break;
            case 'R': // readonly
                break;
            case 'C': // copy 
                break;
            case '&': // retain
                break;
            case 'N': // nonatomic 
                break;
            case 'G': // custom getter
                break;
            case 'S': // custom setter
                break;
            case 'D': // dynamic 
                break;
            default: 
                break;
        }
    }
    free(propertyAttributes);
}
free(properties);

Answer 4

I use the following Category on NSObject to say, for example, NSLog(@"%@", [someObject propertiesPlease]);, resulting in a log entry like…

someObject: {
    color = "NSCalibratedRGBColorSpace 0 0 1 1";
    crayon = Blueberry;
}

NSObject+Additions.h

@interface NSObject (Additions)
- (NSDictionary *)propertiesPlease;
@end

NSObject+Additions.m

@implementation NSObject (Additions)
- (NSDictionary *)propertiesPlease {
NSMutableDictionary *props = [NSMutableDictionary dictionary];
unsigned int outCount, i;
objc_property_t *properties = class_copyPropertyList([self class], &outCount);
for (i = 0; i < outCount; i++) {
   objc_property_t property = properties[i];
   NSString *propertyName = [[NSString alloc] initWithCString:property_getName(property)];
   id propertyValue = [self valueForKey:(NSString *)propertyName];
   if (propertyValue) [props setObject:propertyValue forKey:propertyName];
}
   free(properties);
   return props;
}
@end