Objective–C Style Guide

Comments

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.

Naming

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 class names and constants, however may be omitted for Core Data entity names. For any official raywenderlich.com books, starter kits, or tutorials, the prefix 'RWT' should be used.

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

Preferred:

static NSTimeInterval const RWTTutorialViewControllerNavigationFadeAnimationDuration = 0.3;

Not Preferred:

static NSTimeInterval const fadetime = 1.7;

Properties should be camel-case with the leading word being lowercase. Use auto-synthesis for properties rather than manual @synthesize statements unless you have good reason.

Preferred:

@property (strong, nonatomic) NSString *descriptiveVariableName;

Not Preferred:

id varnm;

Underscores

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.

Methods

In method signatures, there should be a space after the method type (-/+ 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.

Dot-Notation Syntax

Dot-notation should always be used for accessing and mutating properties. Bracket notation is preferred in all other instances.

For example:

view.backgroundColor = [UIColor orangeColor];
[UIApplication sharedApplication].delegate;

Not:

[view setBackgroundColor:[UIColor orangeColor]];
UIApplication.sharedApplication.delegate;

Code Organization

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 {}

Spacing

Indent using 4 spaces. Never indent with tabs. Be sure to set this preference in Xcode.
Method braces and other braces (if/else/switch/while etc.) always open on the new line as the statement and close on a new line.

For example:

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.
@synthesize and @dynamic should each be declared on new lines in the implementation.

Conditionals

Conditional bodies can be used without braces if it is one line only.

For example:

if (!error)
    return success;

Not:

if (!error) {
    return success;
}

or

if (!error)
{
    return success;
}

or

if (!error) return success;

Ternary Operator

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.

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;

Methods

In method signatures, there should be a space after the scope (-/+ symbol). There should be a space between the method segments.

For Example:

- (void)setExampleText:(NSString *)text image:(UIImage *)image;

Variables

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

Asterisks indicating pointers belong with the variable, i.e. NSString *text not NSString* text or NSString * text, except in the case of global string constants.

Property definitions should be used in place of naked instance variables whenever possible. Direct instance variable access should be avoided except in dealloc methods and within custom setters and getters.

For example:

@interface NYTSection: NSObject

@property (nonatomic) NSString *headline;

@end

Not:

@interface NYTSection : NSObject {
    NSString *headline;
}

Naming

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.

For example:

UIButton *settingsButton;

Not

UIButton *setBut;

A three letter prefix (e.g. NYT) should always be used for class names and 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.

For example:

static const NSTimeInterval NYTArticleViewControllerNavigationFadeAnimationDuration = 0.3;

Not:

static const NSTimeInterval fadetime = 1.7;

Properties should be camel-case with the leading word being lowercase. If Xcode can automatically synthesize the variable, then let it. Otherwise, in order to be consistent, the backing instance variables for these properties should be camel-case with the leading word being lowercase and a leading underscore. This is the same format as Xcode's default synthesis.

For example:

@synthesize descriptiveVariableName = _descriptiveVariableName;

Not:

id varnm;

Underscores

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.. Local variables should not contain underscores.

Comments

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. This does not apply to those comments used to generate documentation.

Literals

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

For example:

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

Not:

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 *ZIPCode = [NSNumber numberWithInteger:10018];

Longer or more complex literals should be split over multiple lines (optionally with a terminating comma):

NSArray *theShit = @[
    @"Got some long string objects in here.",
    [AndSomeModelObjects too],
    @"Moar strings."
];

NSDictionary *keyedShit = @{
    @"this.key": @"corresponds to this value",
    @"otherKey": @"remoteData.payload",
    @"some": @"more",
    @"JSON": @"keys",
    @"and": @"stuff",
};

CGRect Functions

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.

For example:

CGRect frame = self.view.frame;

CGFloat x = CGRectGetMinX(frame);
CGFloat y = CGRectGetMinY(frame);
CGFloat width = CGRectGetWidth(frame);
CGFloat height = CGRectGetHeight(frame);

Not:

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;

Constants

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.

For example:

static NSString * const NYTAboutViewControllerCompanyName = @"The New York Times Company";  

static const CGFloat NYTImageThumbnailHeight = 50.0;

Not:

#define CompanyName @"The New York Times Company"

#define thumbnailHeight 2

Enumerated Types

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()

Example:

typedef NS_ENUM(NSInteger, NYTAdRequestState) {
    NYTAdRequestStateInactive,
    NYTAdRequestStateLoading
};

Init Methods

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.

Class Constructor Methods

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:(RWTAirplaneType)type;
@end

Private Properties

Private properties should be declared in class extensions (anonymous categories) in the implementation file of a class. Named categories (such as NYTPrivate or private) should never be used unless extending another class.

For example:

@interface NYTAdvertisement ()

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

@end

Image Naming

Image names should be named consistently to preserve organization and developer sanity. They should be named as one camel case string with a description of their purpose, followed by the un-prefixed name of the class or property they are customizing (if there is one), followed by a further description of color and/or placement, and finally their state.

For example:

RefreshBarButtonItem / RefreshBarButtonItem@2x and RefreshBarButtonItemSelected / RefreshBarButtonItemSelected@2x
ArticleNavigationBarWhite / ArticleNavigationBarWhite@2x and ArticleNavigationBarBlackSelected / ArticleNavigationBarBlackSelected@2x.

Images that are used for a similar purpose should be grouped in respective groups in an Images folder.

Booleans

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.

For example:

if (!someObject)
{
}

Not:

if (someObject == nil) {
}

For a BOOL, here's two examples:

if (isAwesome)
if (![someObject boolValue])

Not:

if ([someObject boolValue] == NO)
if (isAwesome == YES) // Never do this.

Golden Path

When coding with conditionals, the left hand margin of the code should be the "golden" or "happy" path. That is, don't nest 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
   }
}

Error handling

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).

If the name of a BOOL property is expressed as an adjective, the property can omit the “is” prefix but specifies the conventional name for the get accessor, for example:

@property (assign, getter=isEditable) BOOL editable;

Text and example taken from the Cocoa Naming Guidelines.

Singletons

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;
}

This will prevent [possible and sometimes prolific crashes] (http://cocoasamurai.blogspot.com/2011/04/singletons-your-doing-them-wrong.html).

Xcode project

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.

License

Original is here - https://github.com/NYTimes/objective-c-style-guide

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README.md

README.md

Objective–C Style Guide

Table of Contents

Comments

Naming

Underscores

Methods

Dot-Notation Syntax

Code Organization

Spacing

Conditionals

Ternary Operator

Methods

Variables

Naming

Underscores

Comments

Literals

CGRect Functions

Constants

Enumerated Types

Init Methods

Class Constructor Methods

Private Properties

Image Naming

Booleans

Golden Path

Error handling

Singletons

Categories

Xcode project

License

Files

README.md

Latest commit

History

README.md

File metadata and controls

Objective–C Style Guide

Table of Contents

Comments

Naming

Underscores

Methods

Dot-Notation Syntax

Code Organization

Spacing

Conditionals

Ternary Operator

Methods

Variables

Naming

Underscores

Comments

Literals

CGRect Functions

Constants

Enumerated Types

Init Methods

Class Constructor Methods

Private Properties

Image Naming

Booleans

Golden Path

Error handling

Singletons

Categories

Xcode project

License