How to print (using NSLog) all properties of a class automatically?

Question

I think it\'s very difficult to print out the value of all properties of any class in objective-c, in the case the type of the property is complex.

But if the class that

Answer 1

You can do this by overriding -(void)description method.

Example: Let's say we have simple Car class.

@interface Car : NSObject

@property (copy, nonatomic)   NSString *model;
@property (copy, nonatomic)   NSString *make;
@property (strong, nonatomic) NSDate *registrationDate;
@property (assign, nonatomic) NSInteger mileage;
@property (assign, nonatomic) double fuelConsumption;

@end

@implementation
- (NSString*)description {
    return [NSString stringWithFormat:@"<%@:%p %@>",
            [self className],
            self,
            @{ @"model"           : self.model,
               @"make"            : self.make,
               @"registrationDate": self.registrationDate,
               @"mileage"         : @(self.mileage),
               @"fuelConsumption" : @(self.fuelConsumption)
            }];
}
@end

Putting this in NSDictionary will create very nice output in console.

On the other hand, you can create category on NSObject class and do something like this:

- (NSString*)myDescriptionMethod {
    NSMutableDictionary *dict = [NSMutableDictionary new];
    unsigned int count;
    objc_property_t *properties = class_copyPropertyList([self class], &count);

    for (int i = 0; i < count; i++) {
        const char *property = property_getName(properties[i]);
        NSString *propertyString = [NSString stringWithCString:property encoding:[NSString defaultCStringEncoding]];
        id obj = [self valueForKey:propertyString];
        [dict setValue:obj forKey:propertyString];
    }

    free(properties);
    return [NSString stringWithFormat:@"<%@ %p %@>",
            [self class],
            self,
            dict];
}

Then you will avoid overriding -(void)description method in your classes.

Get it from here

Answer 2

The most elegant way to achieve what you're looking for in Objective-C with NSObject subclasses, it to override the NSObject method description.

For example (assuming your Class has a property called propertyX):

-(NSString *)description
{
  return [NSString stringWithFormat:@"<myCustomObject: %@, propertyX: %f, %f>",
                 [self objectID], [self propertyX].x, [self propertyX].y];
}

The default description implementation of NSObject will simply return the memory address pointed to for the object, like so:

NSLog(@"%@", self);

2015-06-15 14:20:30.123 AppName[...] myCustomObject: 0x000000>

However, by overriding this base Class method as shown above, you will be able to customise this behavior, and the log will look like this:

2015-06-15 14:20:30.123 AppName[...] myCustomObject: 0x000000 someProperty, Property: blah, blah>

There is a nice tutorial, which discusses this further here.

Answer 3

Example :-

 + (NSString *)description;
    [NSString description];

Gives you information about the class NSString.