How to create a ICNS icon programmatically?

OK this is what I want :

Take some NSImages
Add them to an ICNS file
Save it

This is what I've done so far (purely as a test) :

- (CGImageRef)refFromImage:(NSImage*)img
{
    CGImageSourceRef source;

    source = CGImageSourceCreateWithData((CFDataRef)[img TIFFRepresentation], NULL);
    CGImageRef maskRef =  CGImageSourceCreateImageAtIndex(source, 0, NULL);

    return maskRef;
}

- (void)awakeFromNib
{
    NSImage* img1 = [NSImage imageNamed:@"image1"];
    NSImage* img2 = [NSImage imageNamed:@"image2"];

    NSLog(@"%@",img1);
    CGImageRef i1 = [self refFromImage:img1];
    CGImageRef i2 = [self refFromImage:img2];

    NSURL *fileURL = [NSURL fileURLWithPath:[@"~/Documents/final.icns" stringByExpandingTildeInPath]]; 
    CGImageDestinationRef dr = CGImageDestinationCreateWithURL((__bridge CFURLRef)fileURL, kUTTypeAppleICNS , 1, NULL);

    CGImageDestinationAddImage(dr, i1, NULL);
    CGImageDestinationAddImage(dr, i2, NULL);
    /* Even tried adding 'multiple' times

    CGImageDestinationAddImage(dr, i1, NULL);
    CGImageDestinationAddImage(dr, i2, NULL);
    CGImageDestinationAddImage(dr, i1, NULL);
    CGImageDestinationAddImage(dr, i2, NULL);

    */

    CGImageDestinationFinalize(dr);

    CFRelease(dr);
}

But, it still keeps throwing an error :

ImageIO: CGImageDestinationFinalize image destination does not have enough images

What's wrong with my code?

I've had a look at the answers below, but still nothing :

Save CGImageRef to PNG file errors? (ARC Caused?)
How exactly to make a CGImageRef from an image on disk

You can use IconFamily.

IconFamily is a Cocoa/Objective-C wrapper for the Mac OS X Carbon API's "icon family" data type. Its main purpose is to enable Cocoa applications to easily create custom file icons from NSImage instances, and thus take advantage of Mac OS X's high-resolution RGBA "thumbnail" icon formats to provide richly detailed thumbnail previews of the files' contents.

NSImage *mImage = [[NSImage alloc] initWithContentsOfFile:@"/Users/Username/Desktop/WhiteTiger.jpg"];
IconFamily *fam = [IconFamily iconFamilyWithThumbnailsOfImage:mImage];    
[fam writeToFile:@"/Users/Username/Desktop/WhiteTiger.icns"];