List of class properties in Objective-C - objective-c

Question

Is there a way to get an array of class properties of certain kind? For example if i have interface like this
#interface MyClass : NSObject
#property (strong,nonatomic) UILabel *firstLabel;
#property (strong,nonatomic) UILabel *secondLabel;
#end
can i get the reference to those labels in implementation without knowing their name?
#implementation MyClass
-(NSArray*)getListOfAllLabels
{
?????
}
#end
I know i can do it easily with [NSArray arrayWithObjects:firstLabel,secondLabel,nil], but i would like to do it with some kind of class enumeration like for (UILabel* oneLabel in ???[self objects]???)

Answer 1

So more precisely, you want dynamic, runtime observaion of the properties, if I got it correctly. Do something like this (implement this method on self, the class you want to introspect):
#import <objc/runtime.h>
- (NSArray *)allPropertyNames
{
unsigned count;
objc_property_t *properties = class_copyPropertyList([self class], &count);
NSMutableArray *rv = [NSMutableArray array];
unsigned i;
for (i = 0; i < count; i++)
{
objc_property_t property = properties[i];
NSString *name = [NSString stringWithUTF8String:property_getName(property)];
[rv addObject:name];
}
free(properties);
return rv;
}
- (void *)pointerOfIvarForPropertyNamed:(NSString *)name
{
objc_property_t property = class_getProperty([self class], [name UTF8String]);
const char *attr = property_getAttributes(property);
const char *ivarName = strchr(attr, 'V') + 1;
Ivar ivar = object_getInstanceVariable(self, ivarName, NULL);
return (char *)self + ivar_getOffset(ivar);
}
Use it like this:
SomeType myProperty;
NSArray *properties = [self allPropertyNames];
NSString *firstPropertyName = [properties objectAtIndex:0];
void *propertyIvarAddress = [self getPointerOfIvarForPropertyNamed:firstPropertyName];
myProperty = *(SomeType *)propertyIvarAddress;
// Simpler alternative using KVC:
myProperty = [self valueForKey:firstPropertyName];
Hope this helps.

Answer 2

use attributeKeys method of NSObject.
for (NSString *key in [self attributeKeys]) {
id attribute = [self valueForKey:key];
if([attribute isKindOfClass:[UILabel class]])
{
//put attribute to your array
}
}

Answer 3

Check out this link. It is an objective c wrapper over objective C runtime.
You can use code like below
uint count;
objc_property_t* properties = class_copyPropertyList(self.class, &count);
NSMutableArray* propertyArray = [NSMutableArray arrayWithCapacity:count];
for (int i = 0; i < count ; i++)
{
const char* propertyName = property_getName(properties[i]);
[propertyArray addObject:[NSString stringWithCString:propertyName encoding:NSUTF8StringEncoding]];
}
free(properties);

Answer 4

You must include the runtime headers
#import<objc/runtime.h>
uint propertiesCount;
objc_property_t *classPropertiesArray = class_copyPropertyList([self class], &propertiesCount);
free(classPropertiesArray);

Answer 5

The answer by #user529758 won't work with ARC and it won't list the properties of any ancestor classes.
To fix this, you need to traverse up the class hierarchy, and use the ARC-compatible [NSObject valueForKey:] to get the property values.
Person.h:
#import <Foundation/Foundation.h>
extern NSMutableArray *propertyNamesOfClass(Class klass);
#interface Person : NSObject
#property (nonatomic) NSString *name;
#end
Person.m:
#import "Person.h"
#import <objc/runtime.h>
NSMutableArray *propertyNamesOfClass(Class klass) {
unsigned int count;
objc_property_t *properties = class_copyPropertyList(klass, &count);
NSMutableArray *rv = [NSMutableArray array];
for (unsigned int i = 0; i < count; i++)
{
objc_property_t property = properties[i];
NSString *name = [NSString stringWithUTF8String:property_getName(property)];
[rv addObject:name];
}
free(properties);
return rv;
}
#implementation Person
- (NSMutableArray *)allPropertyNames {
NSMutableArray *classes = [NSMutableArray array];
Class currentClass = [self class];
while (currentClass != nil && currentClass != [NSObject class]) {
[classes addObject:currentClass];
currentClass = class_getSuperclass(currentClass);
}
NSMutableArray *names = [NSMutableArray array];
[classes enumerateObjectsWithOptions:NSEnumerationReverse usingBlock:^(Class currentClass, NSUInteger idx, BOOL *stop) {
[names addObjectsFromArray:propertyNamesOfClass(currentClass)];
}];
return names;
}
- (NSString*)description {
NSMutableArray *keys = [self allPropertyNames];
NSMutableDictionary *properties = [NSMutableDictionary dictionaryWithCapacity:keys.count];
[keys enumerateObjectsUsingBlock:^(NSString *key, NSUInteger idx, BOOL *stop) {
properties[key] = [self valueForKey:key];
}];
NSString *className = NSStringFromClass([self class]);
return [NSString stringWithFormat:#"%# : %#", className, properties];
}
Student.h:
#import "Person.h"
#interface Student : Person
#property (nonatomic) NSString *studentID;
#end
Student.m:
#import "Student.h"
#implementation Student
#end
main.m:
#import <Foundation/Foundation.h>
#import "Student.h"
int main(int argc, const char * argv[]) {
#autoreleasepool {
// insert code here...
Student *student = [[Student alloc] init];
student.name = #"John Doe";
student.studentID = #"123456789";
NSLog(#"student - %#", student);
}
return 0;
}

Answer 6

The solution of serhats is great unfortunately it doesn't work for iOS (as you mentioned) (and this question is tagged for iOS). A workaround would be to get a NSDictionary representation of the object and then access it normally as key-value pairs. I would recommend a category for NSObject:
Header-File:
#interface NSObject (NSDictionaryRepresentation)
/**
Returns an NSDictionary containing the properties of an object that are not nil.
*/
- (NSDictionary *)dictionaryRepresentation;
#end
Implementation-File:
#import "NSObject+NSDictionaryRepresentation.h"
#import <objc/runtime.h>
#implementation NSObject (NSDictionaryRepresentation)
- (NSDictionary *)dictionaryRepresentation {
unsigned int count = 0;
// Get a list of all properties in the class.
objc_property_t *properties = class_copyPropertyList([self class], &count);
NSMutableDictionary *dictionary = [[NSMutableDictionary alloc] initWithCapacity:count];
for (int i = 0; i < count; i++) {
NSString *key = [NSString stringWithUTF8String:property_getName(properties[i])];
NSString *value = [self valueForKey:key];
// Only add to the NSDictionary if it's not nil.
if (value)
[dictionary setObject:value forKey:key];
}
free(properties);
return dictionary;
}
#end
Borrowed from this article: http://hesh.am/2013/01/transform-properties-of-an-nsobject-into-an-nsdictionary/
This way you could do something similar as serhats mentioned:
for (NSString *key in objectDic.allKeys) {
if([objectDic[key] isKindOfClass:[UILabel class]])
{
//put attribute to your array
}
}