Question

I made this method

-(NSMutableArray *)getProperties:(id)c
{
    NSString *propertyName;
    unsigned int outCount, i;
    NSMutableArray *propertieNames = [[NSMutableArray alloc] initWithObjects: nil];

    objc_property_t *properties = class_copyPropertyList(c, &outCount);
    for (i = 0; i < outCount; i++) {
        objc_property_t property = properties[i];
        propertyName = [NSString stringWithUTF8String:property_getName(property)];
        [propertieNames addObject:propertyName];
    }
    return propertieNames;
}

I use this

NSMutableArray *propertiesNames = [self getProperties:[self class]];

I want to use this

NSMutableArray *propertiesNames = [[self class] getProperties];

How to add category to Class class.　maybe Class class is not Object….

I try add category to Class

#import "Class+SN.h"

@implementation Class (SN)

@end

I got error

Cannot find interface declaration for 'Class'

Answer 1

If you want a class method, you have to use + instead of -. In class methods, self refers to the class, so you can replace c with self. The documentation for class_copyPropertyList says that you need to free the list later with free(), otherwise you are leaking memory.

+ (NSArray *) getProperties
{
    NSString *propertyName;
    unsigned int outCount, i;
    NSMutableArray *propertyNames = [NSMutableArray array];

    objc_property_t *properties = class_copyPropertyList(self, &outCount);
    for (i = 0; i < outCount; i++)
    {
        objc_property_t property = properties[i];
        propertyName = [NSString stringWithUTF8String:property_getName(property)];
        [propertyNames addObject:propertyName];
    }

    free(properties);

    return propertyNames;
}

Also, Objective-C method names rarely use get. Many methods with get in the name imply that they have output parameters or that the caller should provide their own buffer (for examples of when to use get in the name, see getCharacters:range:, and also getStreamsToHost:port:inputStream:outputStream:). This convention means your method would be more appropriately named properties or classProperties etc.