Question

I want to create an Objective-C base class that performs an operation on all properties (of varying types) at runtime. Since the names and types of the properties will not always be known, how can I do something like this?

@implementation SomeBaseClass

- (NSString *)checkAllProperties
{
    for (property in properties) {
        // Perform a check on the property
    }
}

EDIT: This would be particularly useful in a custom - (NSString *)description: override.

Answer 1

To expand on mvds’ answer (started writing this before I saw his), here’s a little sample program that uses the Objective-C runtime API to loop through and print information about each property in a class:

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

@interface TestClass : NSObject

@property (nonatomic, retain) NSString *firstName;
@property (nonatomic, retain) NSString *lastName;
@property (nonatomic) NSInteger *age;

@end

@implementation TestClass

@synthesize firstName;
@synthesize lastName;
@synthesize age;

@end

int main(int argc, char *argv[]) {
    @autoreleasepool {
        unsigned int numberOfProperties = 0;
        objc_property_t *propertyArray = class_copyPropertyList([TestClass class], &numberOfProperties);

        for (NSUInteger i = 0; i < numberOfProperties; i++)
        {
            objc_property_t property = propertyArray[i];
            NSString *name = [[NSString alloc] initWithUTF8String:property_getName(property)];
            NSString *attributesString = [[NSString alloc] initWithUTF8String:property_getAttributes(property)];
            NSLog(@"Property %@ attributes: %@", name, attributesString);
        }
        free(propertyArray);
    }
}

Output:

Property age attributes: T^q,Vage
Property lastName attributes: T@”NSString”,&,N,VlastName
Property firstName attributes: T@”NSString”,&,N,VfirstName

Note that this program needs to be compiled with ARC turned on.