My-Objective-C-Style-Guide

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Table of Contents

• Language
• Operators
• Types
• Code Organization
• Spacing
• Comments
• Naming
  • Underscores
• Methods
• Variables
• Property Attributes
• Dot-Notation Syntax
• Literals
• Constants
• Enumerated Types
• Bitmasks
• Case Statements
• Private Properties
• Image Naming
• Booleans
• Conditionals
  • Ternary Operator
• Init Methods
• Class Constructor Methods
• Inheritance & Super
• CGRect Functions
• Golden Path
• Exceptions & Error handling
• Singletons
• Line Breaks
• Imports
• Xcode Project

Language

Even if I'm French, I always use US English for code & comments in order to maintain coherence with Cocoa and third party Framework naming.

Preferred:

UIColor *myColor = [UIColor whiteColor];

Not Preferred:

UIColor *myColour = [UIColor whiteColor];

Operators

NSString *foo = @"bar";
NSInteger answer = 42;
answer += 9;
answer++;
answer = 40 + 2;

The ++, --, etc are preferred to be after the variable instead of before to be consistent with other operators. Operators separated should always be surrounded by spaces unless there is only one operand.

Types

NSInteger and NSUInteger should be used instead of int, long, etc per Apple's best practices and 64-bit safety. CGFloat is preferred over float for the same reasons. This future proofs code for 64-bit platforms.

All Apple types should be used over primitive ones. For example, if you are working with time intervals, use NSTimeInterval instead of double even though it is synonymous. This is considered best practice and makes for clearer code.

Find more informations about these types following these links:

• Foundation Types & Collections
• CGGeometry Reference link to CGFloat
• Foundation Data Types

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

• I use 2 spaces indentation (can be set in Xcode Preferences).

• Every file ends with a newline (better diff display/scoll to end of file).

• Braces for control statements (if/else/switch/while etc.) always open on the same line as the statement but close on a new line.

• Method braces are placed on a newline (in order to avoid copying the opening brace of a method I'd like to expose in my header file).

Preferred:

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

Not Preferred:

- (void)doSomething{
  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.
• Make liberal use of vertical whitespace to divide code into logical chunks.

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
                 }];

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 (e.g. MRC) 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. Two letter prefix is used by Apple and you do not want your work to collide with Apple future Framework/Classes.

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

Preferred:

static NSTimeInterval const MRCHomeViewControllerFadeAnimationDuration = 0.3;

Not Preferred:

static NSTimeInterval const fadetime = 0.3;

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.

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, 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 MRCTutorial : NSObject

@property (strong, nonatomic) NSString *tutorialName;

@end

Not Preferred:

@interface MRCTutorial : NSObject {
  NSString *tutorialName;
}

Property Attributes

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-Notation Syntax

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 concise. Bracket notation is preferred in all other instances.

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;

Literals

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

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.

Preferred:

static NSString * const kMRCRealName = @"Florian PETIT";

static CGFloat const kMRCImageThumbnailHeight = 50.0;

Not Preferred:

#define RealName @"Florian PETIT"

#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()

For Example:

typedef NS_ENUM(NSInteger, MRCLeftMenuTopItemType) {
  MRCLeftMenuTopItemMain,
  MRCLeftMenuTopItemShows,
  MRCLeftMenuTopItemSchedule
};

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

typedef NS_ENUM(NSInteger, MRCGlobalConstants) {
  MRCPinSizeMin = 1,
  MRCPinSizeMax = 5,
  MRCPinCountMin = 100,
  MRCPinCountMax = 500,
};

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

Not Preferred:

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

Bitmasks

When working with bitmasks, use the NS_OPTIONS macro.

For Example:

typedef NS_OPTIONS(NSUInteger, MRCAdCategory) {
  MRCAdCategoryAutos      = 1 << 0,
  MRCAdCategoryJobs       = 1 << 1,
  MRCAdCategoryRealState  = 1 << 2,
  MRCAdCategoryTechnology = 1 << 3
};

Case Statements

Braces are not required for case statements, unless enforced by the complier (if you try to declare a new variable inside a case - remember that a case does not declare a scope of its own). When a case contains more than one line, braces should be added.

switch (condition) {
  case 1:
    // ...
    break;
  case 2: {
    // ...
    // Multi-line example using braces
    break;
  }
  case 3:
    // ...
    break;
  default:
    // ...
    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;
}

When using an enumerated type for a switch, 'default' is not needed. For example:

MRCLeftMenuTopItemType menuType = MRCLeftMenuTopItemMain;

switch (menuType) {
  case MRCLeftMenuTopItemMain:
    // ...
    break;
  case MRCLeftMenuTopItemShows:
    // ...
    break;
  case MRCLeftMenuTopItemSchedule:
    // ...
    break;
}

Private Properties

Private properties should be declared in class extensions (anonymous categories) in the implementation file of a class. Named categories (such as MRCPrivate 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 MRCDetailViewController ()

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

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.

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.

Conditionals

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) {
  return success;
}

Not Preferred:

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;

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:(MRCAirplaneType)type;
@end

More information on instancetype can be found on NSHipster.com.

Inheritance & Super

When should you call super in an overridden method ? The usual rule of thumb is that when you are overriding a method that does some kind of initialization/setup, you should call super first and then do your custom stuff. And when you override some kind of teardown method, you should call super last.

Setup methods are: init..., viewWillAppear, viewDidAppear, setUp.

Teardown methods are: dealloc, viewDidUnload, viewWillDisappear, tearDown.

For Example:

- (void)viewDidLoad
{
  [super viewDidLoad];
  // Documentation does not specify when this should be
  // called, only that it has to be called at "some point"
  // ...
}

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.

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 };

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
  }
}

Exceptions & Error handling

• Don't use exceptions for flow control.

• Use exceptions only to indicate programmer error.

• 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).

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.

Line Breaks

Line breaks should be applied according the 100 column rule I'm using in Xcode (a column guide can be set in preferences). Pretty neat to avoid wrapping when using the splitted Xcode's Assistant Editor.

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];

Imports

Always use @class whenever possible in header files instead of #import since it has a slight compile time performance boost. (In fact the Type is know but the header is not imported so you'll be reducing compiler overhead)

From the Objective-C Programming Guide (Page 38):

The @class directive minimizes the amount of code seen by the compiler and linker, and is therefore the simplest way to give a forward declaration of a class name. Being simple, it avoids potential problems that may come with importing files that import still other files. For example, if one class declares a statically typed instance variable of another class, and their two interface files import each other, neither class may compile correctly.

Apple introduced a new @import directive, starting with Xcode 5 you can enable module feature from your target build settings and enable the Link Frameworks Automatically option to automatically import frameworks 'on-the-fly' while using @import, this directive also reduces compiler overhead. Have a look Here

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.

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Other Style guides that may influence your coding style:

• NY-Times Objective-C Style Guide
• Apple Coding Guidelines for Cocoa
• Apple Programming with Objective-C
• Apple Avoid Category Method Name Clashes
• Google Objective-C Style Guide
• Raywenderlich Style Guide
• Github Objective-C Conventions
• Sam Soffes Style Guide
• Luke Redpath Style Guide