Get property name as a string

I need a way to pass a property and get the name assigned to it. Any suggestions?

@property (nonatomic, retain) MyObject *crazyObject;

NSString *str = SOME_WAY_TO_GET_PROPERTY_NAME(crazyObject);
// Above method should return @"crazyObject"

Solution 1:

You can try this:

unsigned int propertyCount = 0;
objc_property_t * properties = class_copyPropertyList([self class], &propertyCount);

NSMutableArray * propertyNames = [NSMutableArray array];
for (unsigned int i = 0; i < propertyCount; ++i) {
  objc_property_t property = properties[i];
  const char * name = property_getName(property);
  [propertyNames addObject:[NSString stringWithUTF8String:name]];
}
free(properties);
NSLog(@"Names: %@", propertyNames);

Solution 2:

It's as simple as this...expanding upon what Chuck already mentioned:

#ifndef STR_PROP
    #define STR_PROP( prop ) NSStringFromSelector(@selector(prop))
#endif

You then use it like so:

NSString *strProp = STR_PROP(myProperty);

Solution 3:

Background

Keep in mind that properties are really just, to quote Apple, "a syntactical shorthand for declaring a class’s accessor methods." In fact, by itself, the @property declaration doesn't even work. Your @synthesize statement translates the @property into the equivalent of two methods:

- (void)setCrazyObject:(MyObject *)something;
- (MyObject *)crazyObject;

Which one is used depends on the context surrounding your self.crazyObject. (@synthesize also creates a matching instance variable if you didn't do it yourself.) The offshoot of all this is that you can't really translate to and from a property with one single method.

Proposed Solution

You can use what Apple already provides:

NSString *foo = NSStringFromSelector(@selector(myClassProperty));

Or do something custom:

Given that self.crazyObject really translates to either [self crazyObject] or [self setCrazyObject:foo] by the time your code is running, ou'll probably need two methods, like:

- (NSString *)setterStringForProperty:(SEL)prop;
- (NSString *)getterStringForProperty:(SEL)prop;

You might then want at least 2 companion methods such as:

- (SEL)setterForPropertyName:(NSString *)propString;
- (SEL)getterForPropertyName:(NSString *)propString;

Within these methods, you can use the Foundation functions NSStringFromSelector and NSSelectorFromString to convert back and forth between SEL and NSString. Use whatever string manipulations you like to convert back and forth between your setter string (setCrazyObject) and your property name (crazyObject).

A complete solution is hard to provide without knowing the exact use case, but hopefully this provides some more clues for anyone trying to accomplish something similar. There might even be some useful things made possible by combining this approach with Oscar's answer.

Solution 4:

Here is a function that returns the name of an ivar, so basically it not only returns the properties but any ivar of the class. I haven't found a way to get the property directly so I used the ivar trick.

#import <objc/objc.h>

/// -----

- (NSString *)nameOfIvar:(id)ivarPtr
{
    NSString *name = nil;

    uint32_t ivarCount;
    Ivar *ivars = class_copyIvarList([self class], &ivarCount);

    if(ivars)
    {
        for(uint32_t i=0; i<ivarCount; i++)
        {
            Ivar ivar = ivars[i];

            id pointer = object_getIvar(self, ivar);
            if(pointer == ivarPtr)
            {
                name = [NSString stringWithUTF8String:ivar_getName(ivar)];            
                break;
            }
        }

        free(ivars);
    }

    return name;
}