This style guide serves as a way to standardize Objective-C code we write at Punch Through Design.
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 {}
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
}
@synthesize and @dynamic should each be declared on new lines in the implementation.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
}];
Let your code breathe. Spaces are your friend. Use them liberally. They help your code look more organized and easier for most people to read.
Place an extra line between sections of code to create related sections to make your code easier to read.
Preferred:
for (int i = 0; i < PTConstant; i++) {
int newIndex = i + thatOtherVariable;
bool doSomethingAmazing = false;
if (newIndex < PTMaxLimitOfSomething) {
doSomethingAmazing = true;
}
if (doSomethingAmazing) {
[self doThatAmazingThingWithIndex:newIndex];
}
}
for ( int i = 0; i < PTConstant; i++ ) {
int newIndex = i + thatOtherVariable;
bool doSomethingAmazing = false;
if ( newIndex < PTMaxLimitOfSomething ) {
doSomethingAmazing = true;
}
if ( doSomethingAmazing ) {
[self doThatAmazingThingWithIndex:newIndex];
}
}
Not Preferred:
for (int i=0;i<PTConstant;i++) {
int newIndex=i+thatOtherVariable;
bool doSomethingAmazing=false;
if (newIndex<PTMaxLimitOfSomething) {
doSomethingAmazing=true;
}
if (doSomethingAmazing) {
[self doThatAmazingThingWithIndex:newIndex];
}
}
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.
The golden rule: Code says how, comments say why.
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. This may be omitted for Core Data entity names.
The default prefix for Punch Through Design projects should be “PTD”.
Constants should be camel-case with all words capitalized and prefixed by the related class name for clarity.
Preferred:
static NSTimeInterval const PTDTutorialViewControllerNavigationFadeAnimationDuration = 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.
When writing method implementations, opening brackets go on their own line.
Preferred:
- (void)setExampleText:(NSString *)text image:(UIImage *)image
{
// code goes here
}
Not Preferred:
- (void)setExampleText:(NSString *)text image:(UIImage *)image {
// code goes here
}
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 PTDTutorial : NSObject
@property (strong, nonatomic) NSString *tutorialName;
@end
Not Preferred:
@interface PTDTutorial : 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. Constants should be declared as static constants and not #defines unless explicitly being used as a macro.
Preferred:
static NSString * const PTDAboutViewControllerCompanyName = @"Punch Through Design";
static CGFloat const PTDImageThumbnailHeight = 50.0;
Not Preferred:
#define CompanyName @"Punch Through Design"
#define thumbnailHeight 2
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, PTDLeftMenuTopItemType) {
PTDLeftMenuTopItemMain,
PTDLeftMenuTopItemShows,
PTDLeftMenuTopItemSchedule
};
You can also make explicit value assignments (showing older k-style constant definition):
typedef NS_ENUM(NSInteger, PTDGlobalConstants) {
PTDPinSizeMin = 1,
PTDPinSizeMax = 5,
PTDPinCountMin = 100,
PTDPinCountMax = 500
};
Older k-style constant definitions should be avoided unless writing CoreFoundation C code (unlikely).
Not Preferred:
enum GlobalConstants {
kMaxPinSize = 5,
kMaxPinCount = 500
};
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, always include a ‘default’ case that logs unexpected behavior or throws an error. For example:
PTDLeftMenuTopItemType menuType = PTDLeftMenuTopItemMain;
switch (menuType) {
case PTDLeftMenuTopItemMain:
// ...
break;
case PTDLeftMenuTopItemShows:
// ...
break;
case PTDLeftMenuTopItemSchedule:
// ...
break;
default:
NSLog(@"This shouldn't happen!")
break;
}
Private properties should be declared in class extensions (anonymous categories) in the implementation file of a class. Named categories (such as PTDPrivate or private) should never be used unless extending another class. The Anonymous category can be shared/exposed for testing using the
For Example:
@interface PTDDetailViewController ()
@property (strong, nonatomic) GADBannerView *googleAdView;
@property (strong, nonatomic) ADBannerView *iAdView;
@property (strong, nonatomic) UIWebView *adXWebView;
@end
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.
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.
One-liner if statements without braces are dangerous. One-liner if statements with braces are acceptable, as long as there’s space between the braces for the single statement. You should still consider adding newlines if it increases readability.
Preferred:
if (!error) {
return success;
}
or
if (!error) { 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:(PTDAirplaneType)type;
@end
More 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]) {
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;
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).
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.
Lines of code longer than 120 characters should be wrapped to the next line for readability. For example:
self.productsRequest = [[SKProductsRequest alloc] initWithProductIdentifiers:productIdentifiers andProductSelectors:productSelectors];
A long line of code like this should be carried on to the second line adhering to this style guide’s Spacing section (four spaces).
self.productsRequest = [[SKProductsRequest alloc] initWithProductIdentifiers:productIdentifiers
andProductSelectors:productSelectors];
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.
This guide is based on the raywenderlich.com Objective-C Style Guide. We used the Jekyll style guide built by sportngin. Thanks for all your hard work!