This style guide contains suggestions proper code formatting, company conventions, and common patterns.
Creator and maintainer: Oliver Kocsis
This Guide is based on Raywenderlich's objective-c style guide. https://github.com/raywenderlich/objective-c-style-guide
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
- Cocoa Fundamentals Guide
- Coding Guidelines for Cocoa
- iOS App Programming Guide
- Using Swift with Cocoa and Objective-C
- Nullability and Objective-C
- Language
- Code Organization
- Spacing
- Comments
- Naming
- Methods
- Nullability
- Variables
- Property Attributes
- Dot-Notation Syntax
- Literals
- Constants
- Enumerated Types
- Case Statements
- Private Properties
- Booleans
- Conditionals
- Init Methods
- Class Constructor Methods
- CGRect Functions
- Golden Path
- Error handling
- Singletons
- Line Breaks
- Smiley Face
- Xcode Project
US English should be used.
Preferred:
UIColor *myColor = [UIColor whiteColor];Not Preferred:
UIColor *myColour = [UIColor whiteColor];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 {}- Indent using 4 spaces. Never indent with tabs. Be sure to set this preference in Xcode. (The rest of the document uses 2 spaces indentation, this conserves space in print and makes line wrapping less likely, in xcode we use the default 4 spaces.)
- Method braces and other braces (
if/else/switch/whileetc.) 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,
@synthesizeand@dynamicshould each be declared on new lines in the implementation. - Colon-aligning method invocation should often be used, and is a must if the >= 3 parameters. Please do colon align methods containing blocks as Xcode's does.
Preferred:
// colon-aligning makes the block indentation easy to read
[UIView animateWithDuration:1.0
animations:^{
// something
}
completion:^(BOOL finished) {
// something
}];Not Preferred:
[UIView animateWithDuration:1.0 animations:^{
// something
} completion:^(BOOL finished) {
// something
}];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.
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 should always be used for class names and constants, however may be omitted for Core Data entity names. For any official raywenderlich.com books, starter kits, or tutorials, the prefix 'CSA' should be used.
Constants should be camel-case with all words capitalized and prefixed by the related class name for clarity.
Preferred:
static NSTimeInterval const CSATutorialViewControllerNavigationFadeAnimationDuration = 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;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.
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.For better interoperability with future swift code, one must use nullability qualifiers whereever possible.
The easyest way to achieve this is using the NS_ASSUME_NONNULL_BEGIN/NS_ASSUME_NONNULL_END, and wrap all header files to these macros. Then you only need to mark the nullable params and returns, because all the other will be assumed no to be nullable, and therefore the swift caller won't mishandle it to be an optional, when it is guarandied to be non null. For other info please read apple documention.
Preferred:
NS_ASSUME_NONNULL_BEGIN
@interface AAPLList : NSObject <NSCoding, NSCopying>
// ...
- (nullable AAPLListItem *)itemWithName:(NSString *)name;
- (NSInteger)indexOfItem:(AAPLListItem *)item;
@property (copy, nullable) NSString *name;
@property (copy, readonly) NSArray *allItems;
// ...
@end
NS_ASSUME_NONNULL_END
// --------------
self.list.name = nil; // okay
AAPLListItem *matchingItem = [self.list itemWithName:nil]; // warning!Nonnull parameters always need to be checked up on arrival for nil-ness, using NSParameterAssert() function.
Preferred:
.h:
NS_ASSUME_NONNULL_BEGIN
@interface MyClass : NSObject
- (void)someMethodWithNonNullParameter:(NSNumber *) param;
...
}
@end
NS_ASSUME_NONNULL_END
.m:
- (void)someMethodWithNonNullParameter:(NSNumber *) param {
NSParameterAssert(param);
...
}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 CSATutorial : NSObject
@property (strong, nonatomic) NSString *tutorialName;
@endNot Preferred:
@interface CSATutorial : NSObject {
NSString *tutorialName;
}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 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;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 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. Constant names should start with a lower case k, as apple docs say. Constants should be declared as static constants and not #defines unless explicitly being used as a macro.
Preferred:
static NSString * const kCSAAboutViewControllerCompanyName = @"RayWenderlich.com";
static CGFloat const kCSAImageThumbnailHeight = 50.0;Not Preferred:
#define CompanyName @"RayWenderlich.com"
#define thumbnailHeight 2When using application wide constants, one should create a somewhat Constatns.h file and a .m pair for it, so to hide the actual value of the delcared constant into it.
Preferred:
.h file:
FOUNDATION_EXPORT NSString * kBaseUrlStr;.m file:
NSString * kBaseUrlStr = @"codingsans.com";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(). All enum value names should start with the name of the enum itself. CSALeftMenuTopItem -> CSALeftMenuTopItemFirstValue. This is important for swift compatibility.
For Example:
typedef NS_ENUM(NSInteger, CSALeftMenuTopItem) {
CSALeftMenuTopItemMain,
CSALeftMenuTopItemShows,
CSALeftMenuTopItemSchedule
};You can also make explicit value assignments (showing older k-style constant definition):
typedef NS_ENUM(NSInteger, CSAGlobalConstants) {
CSAGlobalConstantsPinSizeMin = 1,
CSAGlobalConstantsPinSizeMax = 5,
CSAGlobalConstantsPinCountMin = 100,
CSAGlobalConstantsPinCountMax = 500,
};Braces are required for case statements.
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: {
//some code
// ** fall-through! **
}
case 2: {
// some other code
// code executed for values 1 and 2
break;
}
case 3: {
// decalration1
// some code
// ** fall-through! **
case 4:
// using declariation1 var
break;
}
default:
// ...
break;
}
When using an enumerated type for a switch, 'default' is not needed. For example:
CSALeftMenuTopItem menuType = CSALeftMenuTopItemMain;
switch (menuType) {
case CSALeftMenuTopItemMain: {
// ...
break;
}
case CSALeftMenuTopItemShows: {
// ...
break;
}
case CSALeftMenuTopItemSchedule: {
// ...
break;
}
}Private properties should be declared in class extensions (anonymous categories) in the implementation file of a class. Named categories (such as CSAPrivate 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 CSADetailViewController ()
@property (strong, nonatomic) GADBannerView *googleAdView;
@property (strong, nonatomic) ADBannerView *iAdView;
@property (strong, nonatomic) UIWebView *adXWebView;
@endObjective-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. Altough it's ain't nice to store value in a boolean other then 1 or 0.
This allows for more consistency across files and greater visual clarity.
Preferred:
if (someObject) {} or if (someObject != nil) {}
if (someObject == nil) {}
if ([anotherObject boolValue] == NO) {}
Not Preferred:
if (!someObject) {}
if (![anotherObject boolValue]) {}
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.
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 == nil) {
return success;
}Not Preferred:
if (!error)
return success;or
if (!error) return success;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 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.
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:(CSAAirplaneType)type;
@endMore information on instancetype can be found on NSHipster.com.
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 };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] == NO) {
return;
}
if (//check if somthing is missing) {
return
}
//Do something important
}Not Preferred:
- (void)someMethod {
if ([someOther boolValue]) {
//Do something important
}
}When methods return an error parameter by reference, switch on the returned value, not the error variable.
Preferred:
NSError *error;
BOOL succ = [self trySomethingWithError:&error];
if (succ == NO) {
// 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).
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 are an important topic since this style guide is focused for print and online readability.
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];Smiley faces are a very prominent style feature of the raywenderlich.com site! It is very important to have the correct smile signifying the immense amount of happiness and excitement for the coding topic. The end square bracket is used because it represents the largest smile able to be captured using ascii art. A half-hearted smile is represented if an end parenthesis is used, and thus not preferred.
Preferred:
:]Not Preferred:
:)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.
If ours doesn't fit your tastes, have a look at some other style guides: