Class Name with a "+" - objective-c

Question

I am working on an iOS project in Xcode and I see some classes that have names with a "+"; for example:
TableViewController+TableView.h and then the class is named: #interface RKTableViewController (TableView) as opposed to RKTableViewController+TableView.
What is this + and the (TableView)? If its subclassing UITableView shouldn't the class be declared as: Subclassed name : Parent class name format?

Answer 1

The + in the filename isn't semantically important. Naming a file "ClassName+CategoryName.h/m" is just a popular convention for naming files containing categories.
#interface RKTableViewController (TableView)
#end
declares a category called "TableView" on the RKTableViewController class. Categories are used to add methods to a class outside its main implementation. See the Apple documentation on categories here: http://developer.apple.com/library/ios/#documentation/cocoa/conceptual/objectivec/chapters/occategories.html

Answer 2

These are categories. The are very helpful at times.
You can add methods to a class by declaring them in an interface file
under a category name and defining them in an implementation file
under the same name. The category name indicates that the methods are
additions to a class declared elsewhere, not a new class. You cannot,
however, use a category to add additional instance variables to a
class.
The methods the category adds become part of the class type. For
example, methods added to the NSArray class in a category are included
as methods the compiler expects an NSArray instance to have in its
repertoire. Methods added to the NSArray class in a subclass, however,
are not included in the NSArray type. (This matters only for
statically typed objects because static typing is the only way the
compiler can know an object’s class.)
Category methods can do anything that methods defined in the class
proper can do. At runtime, there’s no difference. The methods the
category adds to the class are inherited by all the class’s
subclasses, just like other methods.
http://developer.apple.com/library/ios/#documentation/cocoa/conceptual/objectivec/chapters/occategories.html
Example:
Here is an example of a category I use all the time. I don't own NSMutableArray but I would love for there to be a simple move function. Instead of subclassing just to add a simple function I attach a category.
// NSMutableArray+Move.h
#interface NSMutableArray (move)
- (void)moveObjectFromIndex:(NSUInteger)from toIndex:(NSUInteger)to;
#end
// NSMutableArray+Move.m
#implementation NSMutableArray (move)
- (void)moveObjectFromIndex:(NSUInteger)from toIndex:(NSUInteger)to
{
if (to != from) {
id obj = [self objectAtIndex:from];
[self removeObjectAtIndex:from];
if (to >= [self count]) {
[self addObject:obj];
} else {
[self insertObject:obj atIndex:to];
}
}
}
This allows me to do new things with a class thats already been created all over my app. So anywhere I use an NSMutableArray I can call my added method like so
NSMutableArray *myArray = [NSMutableArray arrayWithObjects:#"Object A", #"Object B", #"Object C", nil];
[myArray moveObjectFromIndex:0 toIndex:2];