From akosma wiki

Contents 1 Objective-C Code Standards 1.1 Files, Code Organization and Other Issues 1.2 Brackets 1.3 Instance Variable + Property Naming Standards 1.4 Pointers 1.5 Comments 1.6 Protocols 1.7 Before Committing Code in SCM Systems

Objective-C Code Standards

To improve readability and maintainability, the Objective-C code created by akosma software follows these coding standards:

Files, Code Organization and Other Issues

• Do not include more than one class in the same file. Use one file per class, with the filename matching the name of the class, for easier retrieval.
• Put protocols in a separate file. Do not include protocols in class headers.
• Lines are indented with 4 spaces, which means NO TABS.
• Add a space between numbers, mathematical operators and other symbols.
• Class names use PascalCase, variables and methods use camelCase, constants use ALL_CAPS_WITH_UNDERSCORES.
• Unless they are assigned some value in the declaration, always initialize all pointer variables to nil, no matter whether they are instance fields or not.
• Use the @class statement in header files (for both classes and protocols) whenever possible, instead of #import'ing them, to reduce the number of dependencies between files.

Brackets

• The layout of brackets follows the "Allman" or "ANSI style", with opening bracket in a separate line:

@interface SomeClass : NSObject
{
    // ivars go here
}

• Always use opening brackets, even in one-line blocks, such as the following if and while statements:

while(x == y)
{
    [something message];
}
[other message];

if(x == y)
{
    [something message];
}

Instance Variable + Property Naming Standards

• Against Apple's own recommendation, ivars must have an underscore as prefix.
• Properties have the same name as the ivars they wrap, minus the underscore:

@interface SomeClass : NSObject
{
    NSInteger _ivar;
}
@property (nonatomic) NSInteger ivar;
@end

@implementation SomeClass
@synthesize ivar = _ivar;
@end

• Do not override @synthesized properties with your own code: use @dynamic properties instead, particularly when you are not wrapping an existing ivar.
• Always use accessors to get or set ivars; do not access them directly. This will make your code KVO- and KVC-compliant, and in Objective-C this is important.
• Append the "IBOutlet" decoration to properties, not to ivars:

@interface SomeClass : NSObject
{
    UILabel _ivar;
}
@property (nonatomic, retain) IBOutlet UILabel ivar;
@end

@implementation SomeClass
@synthesize ivar = _ivar;
@end

Pointers

• Pointer variables always feature a space between the class name and the star sign:

- (ReturnClass *)methodName:(ParamClass1 *)param1 another:(ParamClass2 *)param2
{
    SomeOtherClass *variable = [[SomeOtherClass alloc] init];
    return nil;
}

Comments

• Self-documenting code is a myth; always add comments to explain what's going on. More comments is better.
• Add HeaderDocs (there's a menu in Xcode for that) to class and method definitions. These comments can later be extracted using Doxygen or HeaderDoc:

/*!
    @class       SomeController
    @superclass  UIViewController
    @abstract   Does interesting things, indeed.
*/
@interface SomeController : UIViewController 
{
}

/*!
    @method     doSomething
    @abstract   Changes the internal state of the object.
    @discussion Unbelievable things can happen if you call this method.
    @result     Just a float number meaning lots of things.
*/
- (float)doSomething;

Protocols

• Albeit Objective-C is a dynamic language, do not use informal protocols; create explicit files with protocol definitions.
• Put protocol definitions in their own source code files, never in the same file of the class which uses the protocol methods, neither in the class used as delegate.
• Follow Apple's guidelines for naming the methods of a protocol; in particular, make sure that the first parameter of every protocol method is a pointer to the object calling the method:

@protocol SomeControllerDelegate

- (void)someController:(SomeController *)controller didSomethingWithThisObject:(id)object;

• Use the @required and @optional keywords to explicitly separate methods of a protocol which must be implemented from those that should be implemented:

@protocol SomeControllerDelegate
@required
- (void)someController:(SomeController *)controller didSomethingWithThisObject:(id)object;

@optional
- (void)someControllerDidSomethingElse:(SomeController *)controller;
@end

Before Committing Code in SCM Systems

• Do not leave compiler warnings unattended. Objective-C code must always compile without warnings -- warnings must be treated as errors.
• Use the LLVM/Clang Static Analyzer to check your code for memory leaks or unforeseen problems (integrated in Xcode 3.2).
• Run all unit tests.
• Always add a meaningful comment with your commit.