Reverse engineered implementation of -[UIClassSwapper initWithCoder:]

UIClassSwapper.m

@implementation UIClassSwapper

- (instancetype) initWithCoder:(UINibDecoder *)decoder
{
	NSString *className = [decoder decodeObjectForKey:@"UIClassName"];
	NSString *originalClassName = [decoder decodeObjectForKey:@"UIOriginalClassName"];
	
	Class class = NSClassFromString(className);
	Class originalClass = NSClassFromString(originalClassName);
	
	if (!class) {
		NSLog(@"Unknown class %@ in Interface Builder file.\n", className);
	}
	
	id object = [(class ?: originalClass) alloc];
	[decoder replaceObject:self withObject:object];
	if (originalClass != [UICustomObject class]) {
		self = [object initWithCoder:decoder];
	}
	else {
		self = [object init];
	}
	return [self autorelease];
}

@end

If you drag & drop a custom object, i.e. the Object (NSObject) empty cube in a xib or storyboard, its UIOriginalClassName will be UICustomObject and thus will be initialized through init instead of initWithCoder: even if this object conforms to the NSCoding protocol.

Contrary to what you might expect, changing the custom class of a custom object in the IB inspector won’t affect how it’s initialized. If it was created as a custom object, it will always be initialized with the init method, no matter what its custom class is.

@0xced Thanks a ton for posting this. It was very helpful.

@0xced Do you know of any way to make the custom object's UIOriginalClassName something other than UICustomObject and thus, have it initialized with initWithCoder: initializer?
Thanks beforehand!