/IOS-Playground

Coding guidelines

Objective-C Style Guide

Introduction

Here are some of the documents from Apple that informed the style guide. If something isn't mentioned here, it's probably covered in great detail in one of these:

Table of Contents

Dot-Notation Syntax

Dot-notation should always be used for accessing properties. Bracket notation is preferred when using methods and in other instances.

For example:

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

Not:

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

Spacing

  • Indent using 4 spaces. Never indent with tabs. This should be configured on the project.

  • if/else/switch/while and friends should always open on the same line as the statement, conditions like else or do that follow if or while respectively start in the same line where the previous condition ends.

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 should have braces, except when initializing and lazy loading.

Common code

For example:

if (!error) {
    Field *field = [self.collectionView fieldForIndexPath:field];
    return field.isValid;
}

even if it's one line

if (!error) {
    return success;
}

Not:

if (!error)
    return success;

Initializer

- (instancetype)initWithFrame:(CGRect)frame {
    self = [super initWithFrame:frame];
    if (!self) return nil;

    return self;
}

Lazy loading

- (UILabel *)label {
    if (_label) return _label;

    _label = [UILabel new];

    return _label;
}

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.

For example:

result = (a > b) ? x : y;

Not:

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

Error handling

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

For example:

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

Not:

NSError *error = nil;
[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).

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)updatePersonWithName:(NSString *)name
                    andImage:(UIImage *)image;

In the method implementation opening bracket should always be placed in the same line as the last parameter:

For Example:

- (void)updatePersonWithName:(NSString *)name
                    andImage:(UIImage *)image {
    // Implementation
}

In method invocations the parameters should be colon aligned, if the method becomes a cascade consider splitting the logic in several methods.

For Example:

[someObject updatePersonWithName:@"Example Text"
                           image:[UIImage imageNamed:@"Image.png"]
                  andDescription:@"Example description"];

Variables

Variables should be named as descriptively as possible. Abbreviated variable names should be avoided.

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

Property definitions should be used in place of naked instance variables whenever possible. Direct instance variable access 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.

When declaring a strong property, you can leave out the strong keyword as this is the default.

When declaring properties in public headers that contain mutable counterparts (NSString, NSDictionary, NSArray) make sure to include the copy keyword.

For example:

@interface HYPSection: NSObject

@property (nonatomic) NSString *headline;

@end

Not:

@interface HYPSection : 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. HYP) 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 HYPArticleViewControllerNavigationFadeAnimationDuration = 0.3;

Not:

static const NSTimeInterval fadetime = 1.7;

Properties and local variables should be camel-case with the leading word being lowercase.

Instance variables should be camel-case with the leading word being lowercase, and should be prefixed with an underscore. This is consistent with instance variables synthesized automatically by LLVM. If LLVM can synthesize the variable automatically, then let it.

For example:

@synthesize descriptiveVariableName = _descriptiveVariableName;

Not:

id varnm;

Prefer remoteID or localID when naming local or remote foreign keys.

For example:

Note *note;
note.localID = 12; // local
note.remoteID = 10; // from backend

Not:

objc Note *note; note.noteID = 1;


**or**

```objc```
Note *note;
note.noteId = 1;

Pragma marks

Use pragma marks to structure your code. Sort them in a linear fashion, starting with the initialization, lazy loaded properties and other getters followed by the setters.

Private and custom delegate methods are added at the bottom.

Methods that overwrite their parent methods should be grouped in #pragma mark - PARENT_CLASS

#pragma mark - Initializers

#pragma mark - Getters

#pragma mark - Setters

#pragma mark - View life cycle

#pragma mark - Actions

#pragma mark - Notifications

#pragma mark - HYPBaseTableViewController

#pragma mark - UITableViewDelegate

#pragma mark - CustomViewDelegate

#pragma mark - Private methods

init and dealloc

dealloc methods should be placed at the top of the implementation, directly after the @synthesize and @dynamic statements. init should be placed directly below the dealloc methods of any class.

init methods should be structured like this:

- (instancetype)init {
    self = [super init]; // or call the designated initalizer
    if (!self) return nil;

    // Custom initialization

    return self;
}

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 *buildingZIPCode = [NSNumber numberWithInteger:10018];

Literals should be used when accessing NSDictionary or NSArray instances.

NSString *name = names[0];
NSString *productManager = productManagers[@"iPhone"];

Not:

NSString *name = [names objectAtIndex:0];
NSString *productManager = [productManagers objectForKey:@"iPhone"];

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.

They should be located in the class that uses them, if they are shared between classes you can have them in the public header.

For example:

static NSString * const HYPAboutViewControllerCompanyName = @"Hyper";

static const CGFloat HYPImageThumbnailHeight = 50.0f;

static const CGSize HYPImageDefaultSize = {40.0f, 40.0f};

Not:

#define CompanyName @"Hyper"

#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, HYPAdRequestState) {
    HYPAdRequestStateInactive,
    HYPAdRequestStateLoading
};

Private Properties

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

For example:

@interface HYPAdvertisement ()

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

@end

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 are two examples:

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

Not:

if ([someObject boolValue] == NO)
if (isAwesome == YES) // 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.

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.

Attribution

This document is based on the NYTimes Objective-C Style Guide.