GitHub - dbgcode/objective-c-style-guide: A style guide that outlines the coding conventions for DBG iOS Team

# The official DBG Objective-C style guide. This style guide outlines the coding conventions for DBG iOS Team! ## Introduction The reason we made this style guide was so that we could keep the code in our projects nice and consistent - even though we have many different authors working on each project. ## Background 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: * [The Objective-C Programming Language](http://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/ObjectiveC/Introduction/introObjectiveC.html) * [Cocoa Fundamentals Guide](https://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/CocoaFundamentals/Introduction/Introduction.html) * [Coding Guidelines for Cocoa](https://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/CodingGuidelines/CodingGuidelines.html) * [iOS App Programming Guide](http://developer.apple.com/library/ios/#documentation/iphone/conceptual/iphoneosprogrammingguide/Introduction/Introduction.html) ## Table of Contents * [Language](#language) * [Code Organization](#code-organization) * [Spacing](#spacing) * [Comments](#comments) * [Naming](#naming) * [Underscores](#underscores) * [Methods](#methods) * [Variables](#variables) * [Property Attributes](#property-attributes) * [Dot-Notation Syntax](#dot-notation-syntax) * [Literals](#literals) * [Constants](#constants) * [Enumerated Types](#enumerated-types) * [Case Statements](#case-statements) * [Private Properties](#private-properties) * [Booleans](#booleans) * [Conditionals](#conditionals) * [Ternary Operator](#ternary-operator) * [Init Methods](#init-methods) * [Class Constructor Methods](#class-constructor-methods) * [CGRect Functions](#cgrect-functions) * [Early Return](#early-return) * [Error handling](#error-handling) * [Singletons](#singletons) * [Xcode Project](#xcode-project) ## Language US English should be used. **Preferred:** ```objc UIColor *myColor = [UIColor whiteColor]; ``` **Not Preferred:** ```objc UIColor *myColour = [UIColor whiteColor]; ``` ## Code Organization Use `#pragma mark -` to categorize methods in functional groupings and protocol/delegate implementations following this general structure. ```objc #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 same line as the statement but close on a new line. **Preferred:** ```objc if (user.isHappy) { // do something } else { // do something else } ``` **Not Preferred:** ```objc 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. * If 2 or more classes are declared inside a same file, they should be separated using 2 blank lines. * 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:** ```objc // blocks are easily readable [UIView animateWithDuration:1.0 animations:^{ // something } completion:^(BOOL finished) { // something }]; ``` **Not Preferred:** ```objc // 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. Comments should start with lower-case letters and should be single line. 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.* **Preferred:** ```objc // this type of commenting is preferred // short, sweet! [UIView animateWithDuration:1.0 animations:^{ // something } completion:^(BOOL finished) { // something }]; ``` **Not Preferred:** ```objc /* This type of commenting is not preffered. It starts with an upper-case letter and is multiline. Big, Ugly!*/ [UIView animateWithDuration:1.0 animations:^{ // something } completion:^(BOOL finished) { // something }]; ``` ## Naming Apple naming conventions should be adhered to wherever possible, especially those related to [memory management rules](https://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/MemoryMgmt/Articles/MemoryMgmt.html) ([NARC](http://stackoverflow.com/a/2865194/340508)). Long, descriptive method and variable names are good. **Preferred:** ```objc UIButton *buttonSettings; ``` **Not Preferred:** ```objc UIButton *butSet; ``` A prefix should always be used for class names and constants, however may be omitted for Core Data entity names. Prefixes can be based on the project name. In case the prefix cannot be derived from the project name, "DBG" should be used as the prefix. Constants should be camel-case with all words capitalized and prefixed by the related class name for clarity. **Preferred:** ```objc static NSTimeInterval const DBGTutorialViewControllerNavigationFadeAnimationDuration = 0.3; ``` **Not Preferred:** ```objc 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. UI element properties (like UIButton, UILabel, etc) should be prefixed by the UI element name without the prefix. Model properties (like FYMUser, DBGEmployee) should be prefixed by the model name without the prefix. **Preferred:** ```objc // using camel-case with leading word being lower-case @property (strong, nonatomic) NSString *descriptiveVariableName; // element name prefixed for UI element property @property (strong, nonatomic) UIButton *buttonSomeName; // class name prefixed for model property @property (strong, nonatomic) NSString *employeeName; ``` **Not Preferred:** ```objc 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. **Preferred:** ```objc // some method accessing/updating a property - (void)someMethod { // accessing a property NSString *propertyValue = self.someProperty; // updating a property self.someProperty = @"some new value"; } // some setter method - (void)setSomeProperty:(NSString *)someProperty { // should use underscore inside property accessors _someProperty = someProperty; } ``` **Not Preferred:** ```objc // some method accessing/updating a property - (void)someMethod { // accessing a property NSString *propertyValue = _someProperty; // updating a property _someProperty = @"some new value"; } // some setter method - (void)setSomeProperty:(NSString *)someProperty { // should not use self inside property accessors self.someProperty = someProperty; } ``` ## 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:** ```objc - (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:** ```objc -(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](#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](https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/MemoryMgmt/Articles/mmPractical.html#//apple_ref/doc/uid/TP40004447-SW6). **Preferred:** ```objc @interface DBGTutorial : NSObject @property (strong, nonatomic) NSString *tutorialName; @end ``` **Not Preferred:** ```objc @interface DBGTutorial : NSObject { // avoid doing this // use properties instead 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:** ```objc @property (weak, nonatomic) IBOutlet UIView *containerView; @property (strong, nonatomic) NSString *tutorialName; ``` **Not Preferred:** ```objc @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:** ```objc @property (copy, nonatomic) NSString *tutorialName; ``` **Not Preferred:** ```objc @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](https://developer.apple.com/library/ios/documentation/cocoa/conceptual/ProgrammingWithObjectiveC/EncapsulatingData/EncapsulatingData.html) 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:** ```objc // derived properties like count can be viewed as methods NSInteger arrayCount = [self.array count]; view.backgroundColor = [UIColor orangeColor]; [UIApplication sharedApplication].delegate; ``` **Not Preferred:** ```objc 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:** ```objc 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:** ```objc 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 `#define`s unless explicitly being used as a macro. **Preferred:** ```objc static NSString * const DBGAboutViewControllerCompanyName = @"RayWenderlich.com"; static CGFloat const DBGImageThumbnailHeight = 50.0; ``` **Not Preferred:** ```objc #define CompanyName @"RayWenderlich.com" #define thumbnailHeight 2 ``` ## Enumerated Types When using `enum`s, 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:** ```objc typedef NS_ENUM(NSInteger, DBGLeftMenuTopItemType) { DBGLeftMenuTopItemMain, DBGLeftMenuTopItemShows, DBGLeftMenuTopItemSchedule }; ``` You can also make explicit value assignments (showing older k-style constant definition): ```objc typedef NS_ENUM(NSInteger, DBGGlobalConstants) { DBGPinSizeMin = 1, DBGPinSizeMax = 5, DBGPinCountMin = 100, DBGPinCountMax = 500, }; ``` Older k-style constant definitions should be **avoided** unless writing CoreFoundation C code (unlikely). **Not Preferred:** ```objc 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. ```objc 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. ```objc 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: ```objc DBGLeftMenuTopItemType menuType = DBGLeftMenuTopItemMain; switch (menuType) { case DBGLeftMenuTopItemMain: // ... break; case DBGLeftMenuTopItemShows: // ... break; case DBGLeftMenuTopItemSchedule: // ... break; } ``` ## Private Properties Private properties should be declared in class extensions (anonymous categories) in the implementation file of a class. Named categories (such as `DBGPrivate` 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:** ```objc @interface DBGDetailViewController () @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:** ```objc if (someObject) {} if (![anotherObject boolValue]) {} ``` **Not Preferred:** ```objc 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: ```objc @property (assign, getter=isEditable) BOOL editable; ``` Text and example taken from the [Cocoa Naming Guidelines](https://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/CodingGuidelines/Articles/NamingIvarsAndTypes.html#//apple_ref/doc/uid/20001284-BAJGIIJE). ## Conditionals Conditional bodies should use braces if necessary. In the case, where braces are not necessary (e.g., it is one line only), both conditional statement and the code line should be written in the same line. You should not add a single code line under a conditional statement 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](http://programmers.stackexchange.com/a/16530) 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:** ```objc if (!error) { return success; } ``` or ```objc // this is mainly used while early returning methods if (!error) return success; ``` **Not Preferred:** ```objc 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:** ```objc NSInteger value = 5; result = (value != 0) ? x : y; BOOL isHorizontal = YES; result = isHorizontal ? x : y; ``` **Not Preferred:** ```objc 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'. ```objc - (instancetype)init { if (self = [super init]) { // ... } return self; } ``` See [Class Constructor Methods](#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. ```objc @interface Airplane + (instancetype)airplaneWithType:(DBGAirplaneType)type; @end ``` More information on instancetype can be found on [NSHipster.com](http://nshipster.com/instancetype/). ## CGRect Functions When accessing the `x`, `y`, `width`, or `height` of a `CGRect`, always use the [`CGGeometry` functions](http://developer.apple.com/library/ios/#documentation/graphicsimaging/reference/CGGeometry/Reference/reference.html) 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:** ```objc 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:** ```objc 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 }; ``` ## Early Return Code readability is greatly reduced with the increase in indentation. 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:** ```objc - (void)someMethod { if (![someOther boolValue]) { return; } //Do something important } ``` **Not Preferred:** ```objc - (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:** ```objc NSError *error; if (![self trySomethingWithError:&error]) { // Handle Error } ``` **Not Preferred:** ```objc NSError *error; [self trySomethingWithError:&error]; if (error) { // Handle Error } ``` Some of Apples 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. ```objc + (instancetype)sharedInstance { static id sharedInstance = nil; static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{ sharedInstance = [self new]; }); 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](http://boredzo.org/blog/archives/2009-11-07/warnings) as possible. If you need to ignore a specific warning, use [Clang's pragma feature](http://clang.llvm.org/docs/UsersManual.html#controlling-diagnostics-via-pragmas). ## Credits We would like to thank the creators of the [raywenderlich](https://github.com/raywenderlich/objective-c-style-guide) Objective-C Style Guide which provided a solid starting point for this guide to be created and based upon.

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