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"

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);

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);

clozach

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.

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;
}

After searching and debugging i find solution for me...

Added #import <objc/runtime.h>

Methods object_getIvar(id obj, Ivar ivar) send bad access and app crashes. i modify some code and it worked great:

+(NSString*)stringWithProperty:(id)property withClass:(id)controller
{
    NSString *name = nil;

    uint32_t ivarCount;

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

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

            name = [NSString stringWithUTF8String:ivar_getName(ivar)];

            if ([controller valueForKey:name] == property)
            {
                break;
            }
        }

        free(ivars);
    }

    return name;
}

Modifying the solution, it works when your object is allocated already, otherwise it returns nil:-

NSString * NSStringFromProperty(NSObject* property, NSObject* class)
{
    unsigned int propertyCount = 0;
    objc_property_t * properties = class_copyPropertyList([class class], &propertyCount);

    NSString *name = nil;
    for (unsigned int i = 0; i < propertyCount; ++i)
    {
        name = [NSString stringWithUTF8String:property_getName(properties[i])];

        NSObject *object = [class valueForKey:name];

        if (object != nil && object == property)
        {
            break;
        }
        else
        {
            name = nil;
        }
    }
    free(properties);

    return name;
}

From Get property name as string, without using the runtime reference library, just define:

#define propertyKeyPath(property) (@""#property)
#define propertyKeyPathLastComponent(property) [[(@""#property) componentsSeparatedByString:@"."] lastObject]

And then you can do something like this:

 NSLog(@"%@", propertyKeyPathLastComponent(appleStore.storeLocation.street)); //result: street

You may check my approach at Gist to get the string for a property with autocompletion and compile-time check.

How to use:

Get the property name for a class:

@interface AnyClass : NSObject
@property (strong) NSData *data;
@end

// == My approach ==
// C string for a class
PropertyNameForClass(AnyClass, data);    // ==> "data"
// NSString for a class
PropertyStringForClass(AnyClass, data);  // ==> @"data"

// Bad approach (no autocompletion; no compile-time check):
NSString *propertyName = @"data";

Get the property name for a protocol:

@protocol AnyProtocol
@property (strong) NSDate *date;
@end

// C string for a protocol
PropertyNameForProtocol(AnyProtocol, date);    // ==> "date"
// NSString for a protocol
PropertyStringForProtocol(AnyProtocol, date);  // ==> @"date"

You can use

NSString *str = NSStringFromSelector(@selector(crazyObject));

The good thing about this approach is that:

Xcode will autocomplete word crazyObject for you.
When later on you will change the property name from crazyObject to myCrazyObject, Xcode will add a warning saying "unrecognized selector!" -- pretty good for debugging.

I use this method so often, that I even created a function, which allows to write less letters:

NSString * __nonnull sfs(SEL __nonnull theSelector)
{
    if (!theSelector)
    {
        abort();
    }
    return NSStringFromSelector(theSelector);
}

Now your final solution can look like this:

NSString *str = sfs(@selector(crazyObject));

Unconventional, hacky, ugly, late, but... as strong-named as it gets and works like a charm:

#define SOME_WAY_TO_GET_PROPERTY_NAME(p) p == p ? [[[[[[[NSString alloc] initWithCString:#p encoding:NSUTF8StringEncoding] componentsSeparatedByString:@"."] lastObject] componentsSeparatedByString:@" "] lastObject] stringByReplacingOccurrencesOfString:@"]" withString:@""] : @""

Sample usage:

NSLog(SOME_WAY_TO_GET_PROPERTY_NAME(self.customer.surname)); // surname
NSLog(SOME_WAY_TO_GET_PROPERTY_NAME([[self customer] birthDate])); // birthDate
...

来源：https://stackoverflow.com/questions/6615826/get-property-name-as-a-string

标签

objective-c

introspection

objective-c-runtime

declared-property