Tagview Objective-C Style Guide

Apple has already written a widely accepted coding guide for Objective-C. So, before reading this guide, please make sure you've read the Apple's Cocoa Coding Guidelines.

Example

Below is an example that aggregates all the styles guidelines that we are gonna discuss on this document:

Particle.h

#import <Foundation/Foundation.h>
#include <Math.h>
#import "Spring.h"
#import "Vector.h"
#include "UtilityCFunctions.h"

typedef enum Solvers : NSUInteger {
    kEuler = 1,
    kVerlet = 2
} IntegrationMethod;

@interface Particle : NSObject <Springable>

@property (nonatomic, assign) CGFloat friction;
@property (nonatomic, strong) Vector *position;
@property (nonatomic, readonly) Vector *velocity;
@property (nonatomic, assign) IntegrationMethod integrationMethod;
@property (nonatomic, assign, getter = isFixed) BOOL fixed;

+ (Particle *)fixedParticleAtPosition:(Vector *)position;

- (void)initWithPosition:(Vector *)position;
- (void)initWithPosition:(Vector *)position velocity:(Vector *)velocity;

- (void)addForce:(Vector *)force;
- (void)integrate;

@end

Particle.m

@interface Particle ()

@property (nonatomic, strong) Vector *velocity;
@property (nonatomic, strong) Vector *acceleration;
@property (nonatomic, strong) Vector *previousPosition;

@end

@implementation Particle

#pragma mark - Initializers

// Designated initializer
- (id)initWithPosition:(Vector *)position velocity:(Vector *)velocity {
    if (self = [super init]) {
        _friction = 1;
        _position = position;
        _velocity = velocity;
        _acceleration = [[Vector alloc] init];
    }

    return self;
}

- (id)initWithPosition:(Vector *)position {
    Vector *velocity = [[Vector alloc] init];
    return [self initWithPosition:position velocity:velocity];
}


#pragma mark - Class methods

+ (Particle *)fixedParticleAtPosition:(Vector *)position {
    Particle *fixedParticle = [[Particle alloc] initWithPosition:position];
    fixedParticle.fixed = YES;

    return fixedParticle;
}


#pragma mark - Instance methods

- (void)addForce:(Vector *)force {
    [self.acceleration add:force];
}


#pragma mark - Getters and Setters

- (Vector *)previousPosition {
    if (!_previousPosition) {
        _previousPosition = self.position;
    }

    return _previousPosition;
}


#pragma mark - Integration

- (void)integrate {
    switch (self.integrationMethod) {
        case kEuler:
            [self eulerIntegration];
            break;

        case kVerlet:
            [self verletIntegration];
            break;

        default:
            [self eulerIntegration];
    }
}

- (void)eulerIntegration {
    [self.velocity add:self.acceleration];
    [self.velocity multiply:self.friction];
    [self.position add:self.velocity];
    [self.acceleration multiply:0];
}

- (void)verletIntegration {
    self.velocity = [Vector subtractVector:self.position withVector:self.previousPosition];
    self.previousPosition = [self.position clone];
    [self.velocity add:self.acceleration];
    [self.velocity multiply:self.friction];
    [self.position add:self.velocity];
    [self.acceleration multiply:0];
}

@end

Guidelines

Whitespace

Put one space before leading braces, ifs, whiles, fors, switches, and @properties.

// Bad
if(!_name){
    _name = @"Default";
}

// Good
if (!_name) {
    _name = @"Default";
}


// Bad
@property(nonatomic, strong)Vector *velocity;

// Good
@property (nonatomic, strong) Vector *velocity;

Don't put a spaces between parentheses.

// Bad
if ( !_name ) {
    _name = @"Default";
}

// Good
if (!_name) {
    _name = @"Default";
}

Method declaration and invocation

Put a space after the - or +.

// Bad
-(void)activate;

// Good
- (void)activate;

Put a space before the asterisks.

// Bad
- (void)setVelocity:(Vector*)velocity;

// Good
- (void)setVelocity:(Vector *)velocity;

Don't put a spaces on method arguments and on method declarations.

// Bad
User *user = [[User alloc] initWithFirstName: @"Rodrigo" lastName: @"Navarro"];

// Good
User *user = [[User alloc] initWithFirstName:@"Rodrigo" lastName:@"Navarro"];


// Bad
- (void)setVelocity: (Vector *)velocity;

// Good
- (void)setVelocity:(Vector *)velocity;

If you have too many parameters to fit on one line, giving each its own line is preferred. If multiple lines are used, align each using the colon before the parameter.

- (void)initWithPosition:(Vector *)position 
                velocity:(Vector *)velocity 
            acceleration:(Vector *)acceleration {
    ...
}

When the first keyword is shorter than the others, indent the later lines by at least four spaces, maintaining colon alignment:

- (void)position:(Vector *)position
    maximumVelocity:(Vector *)velocity
       acceleration:(Vector *)acceleration {
    ...
}

Container Literals

If the collection fits on one line, put a single space after the opening and before the closing brackets.

// Bad
NSArray *array = @[@"One", @"Two", @"Three"];
NSArray *array = @[@"One",@"Two",@"Three"];

// Good
NSArray *array = @[ @"One", @"Two", @"Three" ];


// Bad
NSDictionary *dict = @{@"firstName":@"Rodrigo", @"lastName":@"Navarro" };

// Good
NSDictionary *dict = @{ @"firstName": @"Rodrigo", @"lastName": @"Navarro" };

If the collection spans more than a single line, place the opening bracket on the same line as the declaration, indent the body by four spaces, and place the closing bracket on a new line that is indented to the same level as the opening bracket.

NSArray *array = @[
    @"One", 
    @"Two", 
    @"Three"
];

Line Breaks

Don't put a line break after ifs, whiles, fors, and switches.

// Bad
if (!_name )
{
    _name = @"Default";
}

// Good
if (!_name) {
    _name = @"Default";
}

Don't put a line break before a method definition block.

// Bad
- (void)initWithPosition:(Vector *)position
{
    ...
}

// Good
- (void)initWithPosition:(Vector *)position {
    ...
}

Put line breaks between @properties and method definitions.

// Bad
@interface Particle : NSObject <Springable>
@property (nonatomic, assign, getter = isFixed) BOOL fixed;
+ (Particle *)fixedParticleAtPosition:(Vector *)position;

// Good
@interface Particle : NSObject <Springable>

@property (nonatomic, assign, getter = isFixed) BOOL fixed;

+ (Particle *)fixedParticleAtPosition:(Vector *)position;

Properties

Always use properties instead of message passing when possible.

// Bad
if ([array count] > 10) {
    ...
}

// Good
if (array.count > 10) {
    ...
}

// Bad
[view setHidden:NO];

// Good
view.hidden = YES;

Don't use getters and setters during object initialization, instead, access the instance variables directly.

// Bad
- (id)initWithPosition:(Vector *)position velocity:(Vector *)velocity {
    if (self = [super init]) {
        self.position = position;
        self.velocity = velocity;
    }

    return self;
}

// Good
- (id)initWithPosition:(Vector *)position velocity:(Vector *)velocity {
    if (self = [super init]) {
        _position = position;
        _velocity = velocity;
    }

    return self;
}

Import vs Include

Choose between #import and #include based on the language of the header that you are including.

• When including a header that uses Objective-C or Objective-C++, use #import
• When including a standard C or C++ header, use #include

#import <Cocoa/Cocoa.h>
#include <CoreFoundation/CoreFoundation.h>
#import "GTMFoo.h"
#include "base/basictypes.h"

For more information on this topic, see this Stackoverflow answer on the subject.