chaseacton / Objective-C-Style-Guide

Guidelines for iOS development

Geek Repo:Geek Repo

Github PK Tool:Github PK Tool

Propeller Objective-C Coding Style Guide

================================

Introduction

The purpose of this styleguide is to keep Propeller code clean, neat and readable so that future coders can more easily read, understand and modify the code.

Version: 1.0.0

Credits

The creation of this style guide was a collaborative effort of Jim Dabrowski and Chase Acton. It is based heavily on the Ray Wenderlich Objective-C Style Guide which, in-turn was influenced by the creators of the New York Times and Robots & Pencils' Objective-C Style Guides.

Table of Contents

Xcode Project Organization

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.

Code Organization

Only public properties and public methods should be declared in the header (.h) files. All private properties, and private methods should be declared in anonymous categories in the implementation (.m) files. All private methods should have a matching declaration in the anonymous category.

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 - IBActions

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

#pragma mark - Public

- (void)publicMethod {}

#pragma mark - Private

- (void)privateMethod {}

#pragma mark - Protocol conformance

// e.g.:
#pragma mark - UITextFieldDelegate

#pragma mark - UITableViewDataSource

#pragma mark - UITableViewDelegate
// ... etc. 

#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 same line as the statement but close on a new 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
                 }];

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;

The four-letter prefix PROP 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.

Preferred:

static NSTimeInterval const PROPTutorialViewControllerNavigationFadeAnimationDuration = 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.

Variables

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

Private properties should be used in place of instance variables whenever possible.

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 PROPTutorial : NSObject

@property (strong, nonatomic) NSString *tutorialName;

@end

Not Preferred:

@interface PROPTutorial : NSObject {
  NSString *tutorialName;
}

Property Attributes

Default property attributes should be omitted. The order of properties should be atomicity then storage.

Preferred:

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

Not Preferred:

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

Properties with mutable counterparts (e.g. NSString) should prefer copy instead of strong.

Preferred:

@property (nonatomic, copy) NSString *tutorialName;

Not Preferred:

@property (nonatomic, strong) NSString *tutorialName;

Dot-Notation Syntax

Dot-notation should always be used for accessing and mutating properties. Bracket notation should always be used when sending messages.

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.

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 PROPAboutViewControllerCompanyName = @"Propeller";

static CGFloat const PROPImageThumbnailHeight = 50.0;

Not Preferred:

#define CompanyName @"Propeller"

#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 includes a macro to facilitate and encourage use of fixed underlying types: NS_ENUM()

For Example:

typedef NS_ENUM(NSInteger, PROPLeftMenuTopItemType) {
  PROPLeftMenuTopItemMain,
  PROPLeftMenuTopItemShows,
  PROPLeftMenuTopItemSchedule
};

You can also make explicit value assignments:

typedef NS_ENUM(NSInteger, PROPGlobalConstants) {
  PROPPinSizeMin = 1,
  PROPPinSizeMax = 5,
  PROPPinCountMin = 100,
  PROPPinCountMax = 500,
};

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

Not Preferred:

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

Case Statements

Braces are not required for case statements, unless enforced by the complier.
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 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:

PROPLeftMenuTopItemType menuType = PROPLeftMenuTopItemMain;

switch (menuType) {
  case PROPLeftMenuTopItemMain:
    // ...
    break;
  case PROPLeftMenuTopItemShows:
    // ...
    break;
  case PROPLeftMenuTopItemSchedule:
    // ...
    break;
}

Private Properties

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

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

@end

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. 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:(PROPAirplaneType)type;
@end

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

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
  }
}

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).

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.

Model Objects

We use JSONModel (https://github.com/icanzilb/JSONModel) to create model objects from the API.

  • Prefix bools with 'is'

Preferred:

@property (nonatomic, readonly) BOOL isOn;

Not Preferred:

@property (nonatomic, readonly) BOOL on;
  • Use full names in most cases. (e.g. 'medication' instead of 'med')
  • For array properties, use either the 'List' suffix or a plural name (e.g. deliveryDevices or deliverDeviceList)
  • Use NSDate whenever possible. Avoid using strings to hold dates
  • Use JSONKeyMapper to map API key names to Objective-C style variable names rather than setting the property's getter

Preferred:

@interface

@property (nonatomic) NSString *type;
@property (nonatomic) NSString *firstName;

@implementation

+ (JSONKeyMapper *)keyMapper{
    return [[JSONKeyMapper alloc] initWithDictionary:@{
                                                       @"typ": @"type",
                                                       @"fnam": @"firstName"
                                                       }];
}

Not Preferred:

@property (nonatomic, getter=type) NSString *typ;
@property (nonatomic, getter=firstName) NSString *fnam;
  • Use propertyIsOptional to set primitive data types as optional
@interface

@property (nonatomic) BOOL isDiscontinued;

@implementation

+ (BOOL)propertyIsOptional:(NSString*)propertyName{
    if ([propertyName isEqualToString:@"isDiscontinued"]){
        return YES;
    }
    return NO;
}

About

Guidelines for iOS development

License:Other