The official Objective-C style guide

• Language
• User interface
• Project structure
• Basic communication patterns
• Controllers
• Resources
• Code Organization
• Spacing
• Comments
• Naming
  • Underscores
• Methods
• Variables
• Property Attributes
• Dot-Notation Syntax
• Literals
• Constants
• Enumerated Types
• Case Statements
• Private Properties
• Booleans
• Conditionals
  • Ternary Operator
• Init Methods
• Class Constructor Methods
• CGRect Functions
• Golden Path
• Error handling
• Singletons
• Line Breaks
• Import resources

US English should be used.

Preferred:

UIColor *myColor = [UIColor whiteColor];

Not Preferred:

UIColor *myColour = [UIColor whiteColor];

Storyboards are more likely to conflict with the versions (git ...) due to their complex XML structure. This makes merger much more difficult than with the code. The code is easier to structure and use common approaches several times. All information is stored in one place. In Interface Builder, you need to find and select the "inspectors" to find what you are looking for. Recommendations: Do not mix everything. When the project started with storyboards, you should continue to use storyboards. For the separation of multiple user flows, it is recommended to split into smaller storyboards if possible.

Create a folder structure for all enclosures:

├─ Models
├─ Views
├─ Controllers
├─ Stores
├─ Helpers

The physical files should be kept in sync with the Xcode project files in order to avoid file sprawl. Any Xcode groups created should be reflected by folders in the filesystem. Code should be grouped not only by type, but also by feature for greater clarity. When possible, always turn on "Treat Warnings as Errors" in the target's Build Settings and enable as many additional warnings as possible. If you need to ignore a specific warning, use Clang's pragma feature.

Recommended to use of CocoaPods when adding libraries to the project.

Delegation: (one to one) The basic principle - one of the most common, one of the best examples is the use of tables and modal controllers. One element transfers responsibility for part of its functionality by reference to the other.

Callback blocks: (one to one) Provides a lower connectivity of code as more optimal for a large number of senders. Notification Center: (one to many) do not require connections between objects, has the smallest connectivity code. The ability to sign several objects at a single event. Distributed throughout the application. Problems can arise for pieces of code that depends on the execution time.

Key-Value Observing (KVO): (one to many) do not require knowledge of the structure of the reciever, does not block the common channel. On the other hand complicated debugging and support.

Pass all the required objects as parameters(dependency injection), instead of adding states to singletons.

+ [[FooDetailsViewController alloc] initWithFoo:(Foo *)foo];

Don't use underscores and dashes / hyphens in names, only CamelCase. Using a hyphen is only allowed to indicate the size. Using the assets is up to the developer.

IconCheckmarkHighlighted.png // Universal, non-Retina
[email protected] // Universal, Retina
IconCheckmarkHighlighted~iphone.png // iPhone, non-Retina
IconCheckmarkHighlighted@2x~iphone.png // iPhone, Retina
IconCheckmarkHighlighted-568h@2x~iphone.png // iPhone, Retina, 4-inch
IconCheckmarkHighlighted~ipad.png // iPad, non-Retina
IconCheckmarkHighlighted@2x~ipad.png // iPad, Retina

Use #pragma mark - to categorize methods in functional groupings and protocol/delegate implementations following this general structure.

#pragma mark - Lifecycle

- (instancetype) init {}
- (void) dealloc {}
- (void) viewDidLoad {}
- (void) viewWillAppear: (BOOL) animated {}
- (void) didReceiveMemoryWarning {}

#pragma mark - Custom Accessors

- (void) setCustomProperty: (id) value {}
- (id) customProperty {}

#pragma mark - IBActions

- (IBAction) submitData: (id) sender {}

#pragma mark - Public

- (void) publicMethod {}

#pragma mark - Private

- (void) privateMethod {}

#pragma mark - Protocol conformance
#pragma mark - UITextFieldDelegate
#pragma mark - UITableViewDataSource
#pragma mark - UITableViewDelegate

#pragma mark - NSCopying

- (id) copyWithZone: (NSZone*) zone {}

#pragma mark - NSObject

- (NSString*) description {}

Method braces and other braces (if/else/switch/while etc.) always open on the next line.

Preferred:

if (user.isHappy) 
{
  //Do something
} else 
{
  //Do something else
}

Not Preferred:

if (user.isHappy){
    //Do something
}
else {
    //Do something else
}

• There should be exactly one blank line between methods to aid in visual clarity and organization. Whitespace within methods should separate functionality, but often there should probably be new methods.
• Prefer using auto-synthesis. But if necessary, @synthesize and @dynamic should each be declared on new lines in the implementation.
• Colon-aligning method invocation should often be avoided. There are cases where a method signature may have >= 3 colons and colon-aligning makes the code more readable. Please do NOT however colon align methods containing blocks because Xcode's indenting makes it illegible.

Preferred:

// blocks are easily readable
[UIView animateWithDuration: 1.0 animations: ^{
  // something
} completion: ^(BOOL finished) {
  // something
}];

Not Preferred:

// colon-aligning makes the block indentation hard to read
[UIView animateWithDuration:1.0
                 animations:^{
                     // something
                 }
                 completion:^(BOOL finished) {
                     // something
                 }];

When they are needed, comments should be used to explain why a particular piece of code does something. Any comments that are used must be kept up-to-date or deleted.

Block comments should generally be avoided, as code should be as self-documenting as possible, with only the need for intermittent, few-line explanations. Exception: This does not apply to those comments used to generate documentation. Comments should be only in english. Transliteration is not allowed.

Class names, methods, variables and so on should discribe purpose as much as possible and each word should begin with a capital letter. Example: "CamelCase". Apple naming conventions should be adhered to wherever possible, especially those related to memory management rules (NARC).

Long, descriptive method and variable names are good.

Preferred:

UIButton *settingsButton;

Not Preferred:

UIButton *setBut;

A three letter prefix should always be used for constants, however may be omitted for Core Data entity names.

Constants should be camel-case with all words capitalized and prefixed by the related class name for clarity.

Preferred:

static NSTimeInterval const 
CSFViewControllerNavigationFadeAnimationDuration = 0.3;

Not Preferred:

static NSTimeInterval const fadetime = 1.7;

Properties should be with the leading word being lowercase, and each subsequent word should begin with a capital letter. Use auto-synthesis for properties rather than manual @synthesize statements unless you have good reason. Always specify attribute of property: atomic, nonatmic, strong, weak, assign, copy.

Preferred:

@property (strong, nonatomic) NSString *descriptiveVariableName;

Not Preferred:

id varnm;

When using properties, instance variables should always be accessed and mutated using self.. This means that all properties will be visually distinct, as they will all be prefaced with self..

An exception to this: inside initializers, the backing instance variable (i.e. _variableName) should be used directly to avoid any potential side effects of the getters/setters.

Local variables should not contain underscores.

In method signatures, there should be a space after the method type (-/+ symbol) and after type of the parameter(befoe * symbol). There should be a space between the method segments (matching Apple's style). Always include a keyword and be descriptive with the word before the argument which describes the argument.

The usage of the word "and" is reserved. It should not be used for multiple parameters as illustrated in the initWithWidth:height: example below.

Preferred:

- (void) setExampleText: (NSString*) text image: (UIImage*) image;
- (void) sendAction: (SEL) aSelector to: (id) anObject forAllCells: (BOOL) flag;
- (id) viewWithTag: (NSInteger) tag;
- (instancetype) initWithWidth: (CGFloat) width height: (CGFloat) height;

Not Preferred:

-(void)setT:(NSString *)text i:(UIImage *)image;
- (void)sendAction:(SEL)aSelector :(id)anObject :(BOOL)flag;
- (id)taggedView:(NSInteger)tag;
- (instancetype)initWithWidth:(CGFloat)width andHeight:(CGFloat)height;
- (instancetype)initWith:(int)width and:(int)height;  // Never do this.

Variables should be named as descriptively as possible. Single letter variable names should be avoided except in for() loops.

Asterisks indicating pointers (* symbol) belong with the variable, e.g., NSString *text not NSString* text or NSString * text, except in the case of constants.

Private properties should be used in place of instance variables whenever possible. Although using instance variables is a valid way of doing things, by agreeing to prefer properties our code will be more consistent.

Direct access to instance variables that 'back' properties should be avoided except in initializer methods (init, initWithCoder:, etc…), dealloc methods and within custom setters and getters. For more information on using Accessor Methods in Initializer Methods and dealloc, see here.

Preferred:

@interface CSFTutorial : NSObject

@property (strong, nonatomic) NSString *tutorialName;

@end

Not Preferred:

@interface CSFTutorial : NSObject {
  NSString *tutorialName;
}

Property attributes should be explicitly listed, and will help new programmers when reading the code. The order of properties should be storage then atomicity, which is consistent with automatically generated code when connecting UI elements from Interface Builder.

Preferred:

@property (weak, nonatomic) IBOutlet UIView *containerView;
@property (strong, nonatomic) NSString *tutorialName;

Not Preferred:

@property (nonatomic, weak) IBOutlet UIView *containerView;
@property (nonatomic) NSString *tutorialName;

Properties with mutable counterparts (e.g. NSString) should prefer copy instead of strong. Why? Even if you declared a property as NSString somebody might pass in an instance of an NSMutableString and then change it without you noticing that.

Preferred:

@property (copy, nonatomic) NSString *tutorialName;

Not Preferred:

@property (strong, nonatomic) NSString *tutorialName;

Dot syntax is purely a convenient wrapper around accessor method calls. When you use dot syntax, the property is still accessed or changed using getter and setter methods. Read more here

Dot-notation should always be used for accessing and mutating properties, as it makes code more short. Bracket notation is preferred in methods.

Preferred:

NSInteger arrayCount = [self.array count];
view.backgroundColor = [UIColor orangeColor];
[UIApplication sharedApplication].delegate;

Not Preferred:

NSInteger arrayCount = self.array.count;
[view setBackgroundColor:[UIColor orangeColor]];
UIApplication.sharedApplication.delegate;

NSString, NSDictionary, NSArray, and NSNumber literals should be used whenever creating immutable instances of those objects. Pay special care that nil values can not be passed into NSArray and NSDictionary literals, as this will cause a crash.

Preferred:

NSArray *names = @[@"Brian", @"Matt", @"Chris", @"Alex", @"Steve", @"Paul"];
NSDictionary *productManagers = @{@"iPhone": @"Kate", @"iPad": @"Kamal", @"Mobile Web": @"Bill"};
NSNumber *shouldUseLiterals = @YES;
NSNumber *buildingStreetNumber = @10018;

Not Preferred:

NSArray *names = [NSArray arrayWithObjects:@"Brian", @"Matt", @"Chris", @"Alex", @"Steve", @"Paul", nil];
NSDictionary *productManagers = [NSDictionary dictionaryWithObjectsAndKeys: @"Kate", @"iPhone", @"Kamal", @"iPad", @"Bill", @"Mobile Web", nil];
NSNumber *shouldUseLiterals = [NSNumber numberWithBool:YES];
NSNumber *buildingStreetNumber = [NSNumber numberWithInteger:10018];

Constants are preferred over in-line string literals or numbers, as they allow for easy reproduction of commonly used variables and can be quickly changed without the need for find and replace. Constants should be declared as static constants and not #defines unless explicitly being used as a macro. Using define reasonable only in the case of a platform / target / enviroment dependent constants.

Preferred:

static NSString * const CSFAboutViewControllerCompanyName = @"Somewebsite.com";

static CGFloat const CSFImageThumbnailHeight = 50.0;

Not Preferred:

#define CompanyName @"SomeWebsite.com"

#define thumbnailHeight 2

To separate the parts written in C or in low-level classes use the constants starting with k.

Preferred:

static float const kADTDefaultItemSize = 50.0f;

When using enums, it is recommended to use the new fixed underlying type specification because it has stronger type checking and code completion. The SDK now includes a macro to facilitate and encourage use of fixed underlying types: NS_ENUM()

For Example:

typedef NS_ENUM(NSInteger, CSFLeftMenuTopItemType) 
{
  CSFLeftMenuTopItemMain,
  CSFLeftMenuTopItemShows,
  CSFLeftMenuTopItemSchedule
};

You can also make explicit value assignments (showing older k-style constant definition):

typedef NS_ENUM(NSInteger, CSFGlobalConstants) 
{
  CSFPinSizeMin = 1,
  CSFPinSizeMax = 5,
  CSFPinCountMin = 100,
  CSFPinCountMax = 500,
};

Older k-style constant definitions should be avoided unless writing CoreFoundation C code (unlikely).

Not Preferred:

enum GlobalConstants {
  kMaxPinSize = 5,
  kMaxPinCount = 500,
};

Braces are required for case statements even when a case contains only one line. Parameter names of the condition must be meaningful, for example, some "enum". Case statement is a good option to select from many states, which makes code more short.

switch (menuType) 
{
  case CSFLeftMenuTopItemMain:
  {
    // …
    // …
  }
    break;
  case CSFLeftMenuTopItemShows:
    // ...
    break;
  case CSFLeftMenuTopItemSchedule:
    // ...
    break;
}

There are times when the same code can be used for multiple cases, and a fall-through should be used. A fall-through is the removal of the 'break' statement for a case thus allowing the flow of execution to pass to the next case value. A fall-through should be commented for coding clarity.

switch (condition) 
{
  case 1:
    // ** fall-through! **
  case 2:
    // code executed for values 1 and 2
    break;
  default: 
    // ...
    break;
}

Private properties should be declared in class extensions (anonymous categories) in the implementation file of a class. Named categories (such as CSFPrivate or private) should never be used unless extending another class. The Anonymous category can be shared/exposed for testing using the +Private.h file naming convention.

For Example:

@interface CSFDetailViewController ()

@property (strong, nonatomic) GADBannerView *googleAdView;
@property (strong, nonatomic) ADBannerView *iAdView;
@property (strong, nonatomic) UIWebView *adXWebView;

@end

Objective-C uses YES and NO. Therefore true and false should only be used for CoreFoundation, C or C++ code. Since nil resolves to NO it is unnecessary to compare it in conditions. Never compare something directly to YES, because YES is defined to 1 and a BOOL can be up to 8 bits.

This allows for more consistency across files and greater visual clarity.

Preferred:

if (someObject) {}
if (![anotherObject boolValue]) {}

Not Preferred:

if (someObject == nil) {}
if ([anotherObject boolValue] == NO) {}
if (isAwesome == YES) {} // Never do this.
if (isAwesome == true) {} // Never do this.

Conditional bodies should always use braces even when a conditional body could be written without braces (e.g., it is one line only) to prevent errors. These errors include adding a second line and expecting it to be part of the if-statement. Another, even more dangerous defect may happen where the line "inside" the if-statement is commented out, and the next line unwittingly becomes part of the if-statement. In addition, this style is more consistent with all other conditionals, and therefore more easily scannable.

Preferred:

if (!error) 
{
}

Not Preferred:

if (someObject == nil){
}

The Ternary operator, ?: , should only be used when it increases clarity or code neatness. A single condition is usually all that should be evaluated. Evaluating multiple conditions is usually more understandable as an if statement, or refactored into instance variables. In general, the best use of the ternary operator is during assignment of a variable and deciding which value to use.

Non-boolean variables should be compared against something, and parentheses are added for improved readability. If the variable being compared is a boolean type, then no parentheses are needed.

Divide code into several lines, if it does not fit in the width of the screen.

Preferred:

NSInteger value = 5;
result = (value != 0) ? x : y;

BOOL isHorizontal = YES;
result = isHorizontal ? x : y;

Not Preferred:

result = a > b ? x = c > d ? c : d : y;

Init methods should follow the convention provided by Apple's generated code template. A return type of 'instancetype' should also be used instead of 'id'.

- (instancetype) init 
{
  self = [super init];
  if (self) 
  {
    // ...
  }
  return self;
}

See Class Constructor Methods for link to article on instancetype.

Where class constructor methods are used, these should always return type of 'instancetype' and never 'id'. This ensures the compiler correctly infers the result type.

@interface Airplane
+ (instancetype) airplaneWithType: (CSFAirplaneType) type;
@end

When accessing the x, y, width, or height of a CGRect, always use the CGGeometry functions instead of direct struct member access. From Apple's CGGeometry reference:

All functions described in this reference that take CGRect data structures as inputs implicitly standardize those rectangles before calculating their results. For this reason, your applications should avoid directly reading and writing the data stored in the CGRect data structure. Instead, use the functions described here to manipulate rectangles and to retrieve their characteristics.

Preferred:

CGRect frame = self.view.frame;

CGFloat x = CGRectGetMinX(frame);
CGFloat y = CGRectGetMinY(frame);
CGFloat width = CGRectGetWidth(frame);
CGFloat height = CGRectGetHeight(frame);
CGRect frame = CGRectMake(0.0, 0.0, width, height);

Not Preferred:

CGRect frame = self.view.frame;

CGFloat x = frame.origin.x;
CGFloat y = frame.origin.y;
CGFloat width = frame.size.width;
CGFloat height = frame.size.height;
CGRect frame = (CGRect){ .origin = CGPointZero, .size = frame.size };

When coding with conditionals, the left hand margin of the code should be the "golden" or "happy" path. That is, don't put a lot of if statements. Multiple return statements are OK.

Preferred:

- (void)someMethod 
{
  if (![someOther boolValue]) 
  {
    return;
  }

  //Do something important
}

Not Preferred:

- (void)someMethod {
  if ([someOther boolValue]) {
    //Do something important
  }
}

When methods return an error parameter by reference, switch on the returned value, not the error variable.

Preferred:

NSError *error;
if (![self trySomethingWithError:&error]) 
{
  // Handle Error
}

Not Preferred:

NSError *error;
[self trySomethingWithError:&error];
if (error) {
  // Handle Error
}

Some of Apple’s APIs write garbage values to the error parameter (if non-NULL) in successful cases, so switching on the error can cause false negatives (and subsequently crash).

Singleton objects should use a thread-safe pattern for creating their shared instance.

+ (instancetype) sharedInstance 
{
  static id sharedInstance = nil;

  static dispatch_once_t onceToken;
  dispatch_once(&onceToken, ^{
    sharedInstance = [[self alloc] init];
  });

  return sharedInstance;
}

Using macros call restricted methods of object creation is allowed. But it is necessary to redefine at least allocWithZone: and copyWithZone:.

Line breaks are an important topic since this style guide is focused for print and online readability.

For example:

self.productsRequest = [[SKProductsRequest alloc] initWithProductIdentifiers: productIdentifiers];

A long line of code like this should be carried on to the second line adhering to this style guide's Spacing section (two spaces).

self.productsRequest = [[SKProductsRequest alloc] 
  initWithProductIdentifiers: productIdentifiers];

CocoaPods

A simple way to connect external dependencies (libraries, components, and so on.). It is recommended to use when connecting CocoaPods libraries, if they do not need to fork.

// Frameworks 
@import QuartzCore;

// Models
#import "NYTUser.h"

// Views
#import "NYTButton.h"
#import "NYTUserView.h"