KidMastermind Objective-C Style Guide

This style guide outlines the coding conventions of the iOS team at KidMastermind.

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:

Credits

We would like to thank the creators of the official raywenderlich.com Objective-C style guide. This style guide provided a solid starting point for this guide to be created and based upon.

Language
Code Organization
Import
- Header Prefix
Spacing
Comments
Naming
- Underscores
Methods
- Method Arguments
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
Boyscout / Girl Guide
Copyrights
Xcode Project

Language

US English should be used.

Preferred:

UIColor *myColor = [UIColor whiteColor];

Not Preferred:

UIColor *myColour = [UIColor whiteColor];

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 {}

Import

Always use @class whenever possible in header files instead of #import since it has a slight compile time performance boost.

From the Object Oriented Programming and the Objective-C Programming Language 1.0 (Page 31):

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.

Header Prefix

Adding frameworks that are used in the majority of a project to a header prefix is preferred. If these frameworks are in the header prefix, they should never be imported in source files in the project.

For example, if a header prefix looks like the following:

#ifdef __OBJC__
    #import <Foundation/Foundation.h>
    #import <UIKit/UIKit.h>
#endif

#import <Foundation/Foundation.h> should never occur in the project outside of the header prefix.

Spacing

Indent using 4 spaces. Never indent with tabs. Be sure to set this preference in Xcode.
Method braces always open and close on a new line.

Preferred:

- (void)someMethod
{
    // Do something important
}

Not Preferred:

- (void)someMethod {
   // Do something important
}

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;

A three letter prefix (e.g. 'KMT') 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 KMTSampleViewControllerNavigationFadeAnimationDuration = 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 (copy, 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.

Method Arguments

There are a few general rules concerning the names of method arguments:

As with methods, arguments start with a lowercase letter and the first letter of successive words are capitalized (for example, removeObject:(id)anObject).
Don’t use “pointer” or “ptr” in the name. Let the argument’s type rather than its name declare whether it’s a pointer.
Avoid one- and two-letter names for arguments.
Avoid abbreviations that save only a few letters.

Traditionally (in Cocoa), the following keywords and arguments are used together:

...action:(SEL)aSelector
...alignment:(int)mode
...atIndex:(int)index
...content:(NSRect)aRect
...doubleValue:(double)aDouble
...floatValue:(float)aFloat
...font:(NSFont *)fontObj
...frame:(NSRect)frameRect
...intValue:(int)anInt
...keyEquivalent:(NSString *)charCode
...length:(int)numBytes
...point:(NSPoint)aPoint
...stringValue:(NSString *)aString
...tag:(int)anInt
...target:(id)anObject
...title:(NSString *)aString

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 KMTArticle : NSObject

@property (copy, nonatomic) NSString *articleName;

@end

Not Preferred:

@interface KMTArticle : NSObject {
    NSString *articleName;
}

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.
Declare properties readonly if they are only set once in -init.
Declare properties copy if they return immutable objects and aren't ever mutated in the implementation. strong should only be used when exposing a mutable object, or an object that does not conform to <NSCopying>.

Preferred:

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

Not Preferred:

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

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 KMTAboutViewControllerCompanyName = @"KidMastermind.com";

static CGFloat const KMTImageThumbnailHeight = 50.0;

Not Preferred:

#define CompanyName @"KidMastermind.com"

#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, KMTLeftMenuTopItemType) {
    KMTLeftMenuTopItemMain,
    KMTLeftMenuTopItemShows,
    KMTLeftMenuTopItemSchedule
};

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

typedef NS_ENUM(NSInteger, KMTGlobalConstants) {
    KMTPinSizeMin = 1,
    KMTPinSizeMax = 5,
    KMTPinCountMin = 100,
    KMTPinCountMax = 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 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:

KMTLeftMenuTopItemType menuType = KMTLeftMenuTopItemMain;

switch (menuType) {
    case KMTLeftMenuTopItemMain:
        // ...
        break;
    case KMTLeftMenuTopItemShows:
        // ...
        break;
    case KMTLeftMenuTopItemSchedule:
        // ...
        break;
}

Private Properties

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

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

Boyscout / Girl Guide

Always leave the code in better condition than you found it.

Copyrights

By default, use a KidMastermind copyright. There may be special circumstances where it should be changed to a customer name.

// Copyright (c) 2014 KidMastermind. All rights reserved.

Set the Organization in your .xcodeproj to override your default company name for new files that are created. Select the project in File Navigator, then use the File Inspector (first button) in the Utilities pane. Set the organization to KidMastermind.

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.

Other Objective-C Style Guides

If ours doesn't fit your tastes, have a look at some other style guides:

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KidMastermind Objective-C Style Guide

Introduction

Credits

Table of Contents

Language

Code Organization

Import

Header Prefix

Spacing

Comments

Naming

Underscores

Methods

Method Arguments

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

Boyscout / Girl Guide

Copyrights

Xcode project

Other Objective-C Style Guides

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