Question

I try to understand how to work simple init funcion and I don’t know where I have made a mistake. Can somebody assist?

Rectangle.h

@interface Rectangle : NSObject
{
    int width;
    int height;
}
-(id)initObject;
@end

Rectangle.m

@implementation Rectangle

-(id)initObject{
    if (self = [super init]) {
        height = 5;
        width = 7;
    }
    return self;
}    

@end

And in ViewController.h i import Rectangle.h, declare *rect object and in .m i execute(? run?) initObject.

ViewController.h

#import <UIKit/UIKit.h>
#import "Rectangle.h"
@interface ViewController : UIViewController
{
    Rectangle *rect;
}
@end

ViewController.m

-(void)viewDidLoad
{
    rect = [[Rectangle alloc] initObject];
    NSLog(@"%@", rect);

    [super viewDidLoad];

}

initObject return me:

 2011-11-21 09:43:02.625 initializers[43693:f803] <Rectangle: 0x6ab1660>

Answer 1

The only problem with your code that I can see is you called your initializer -initObject for no good reason. It’s not taking any parameters at all, so you really should just call it -init like every other parameterless initializer in the system.

As for the log output, I imagine your confusion lies in the fact that it says <Rectangle: 0x6ab1660>. This is perfectly normal. The default implementation of -description (the method that returns this output) is the name of the class of the object followed by the object’s address. In other words, -[NSObject description] is likely to be implemented something like the following:

- (NSString *)description {
    return [NSString stringWithFormat:@"<%@: %p>",
                                      NSStringFromClass([self class]),
                                      self];
}

This means that instance variables of your object are not going to be printed. A number of built-in classes do print their instance variables when logged, but this was implemented specifically for that class and is not a generic mechanism. If you want to verify that your Rectangle object is correct, you could implement -description like so:

- (NSString *)description {
    return [NSString stringWithFormat:@"<%@: %p width=%d, height=%d>",
                                      NSStringFromClass([self class]),
                                      self,
                                      width,
                                      height];
}