iOS Guidelines

Project Structure

Organized .xcodeproj: files are grouped by layers (Presentation, Domain/Model, Infrastructure, etc), responsibilities (UI, Model, Logic, Vendor, etc), roles, etc. No flat structure allowed
Organized project folder: desirable but not required to keep file structure in sync with .xcodeproj
One .m / .swift == One class. No extra classes allowed
Localization is required even for the case, when you have only one language. Therefore adding extra language won't cause any difficulty in future
Images and other resources (.plist) should be grouped as well (i.e. $SRCROOT/Resources/Images/Common/, $SRCROOT/Resource/Assets/)

File Structure (.m)

Structure

imports

related constants

class extension

@implementation
- dealloc
- init methods
- other
@end

Method sections should be separated by #pragma mark - $sectionName

Braces, Asterisk

Curly braces are opened on the same line with code, closed - on a new line. For short blocks / closures a single line can be used
Asterisk placed near the name Type *var = ...;
Every code block should be wrapped by {}:

if (statement) {
    NSLog(@"%@", var);
}

The only exception is a short statement and an immediate return in the beginning:

- (void)performSomeTask {
    if (!user.hasToken) return;
    ...
}

Spaces, Formatting

General

Tab consists of 4 spaces
Max symbols in a row: 120
Use space after if, while, for and similar:

if (pointer != someOtherPointer)

CGFloat result = width * height * 2.f;

BOOL contentExists = self.content.length > 0;

for (int i = 0; i < x; i++) { ... }

Alignment: do not align code as ASCII-art.
Separate logical code blocks with 1 line wrap. Random number of \n is not allowed

Variable declaration

Between Type & Protocol there are no spaces: id<NSObject> object = ...;
Between var and casting parentheses there are no spaces: ClassType *a = (ClassType *)b;, ScalarType a = (ScalarType)b;

Class Declaration

If listing protocols goes beyond 120 characters, place each on a separate line:

@interface SCHCategoryViewController : UIViewController <UITableViewDelegate> 

@interface SCHCategoryViewController : UIViewController <
    UITableViewDelegate, 
    UITableViewDataSource, 
    SCHSyncronizationDelegate
>

Method Declaration

Use a single space between +/- and a returned type. Any additional spaces in arguments list are not allowed: - (void)doSomethingWithString:(NSString *)string flag:(BOOL)flag;
If the method goes beyond 120+10 characters, place each argument on a separate line, align by colon:

- (void)doSomethingWithString:(NSString *)string
                         rect:(CGRect)rectangle
                       length:(NSUInteger)length;

Method Invocation

Method invocation should use the same formatting as for declaration

Function Declaration

No space symbol between name and arguments parentheses
If the method goes beyond 120+10 characters, parentheses should be placed the same way, as opening/closing braces. Place each argument on a separate line aligned by 1 tab:

void * LongLongLongFunction(
    id firstArgument, 
    id secondArgument,
    id *outArgument,
    int other
)

NSAssert(
    [controller conformsToProtocol:@protocol(EParticipantSelection)],
    @"Controller %@ should confrom to protocol",
    NSStringFromProtocol(@protocol(EParticipantSelection))
);

Access specifiers & ivars

@public, @private, @protected should be aligned by 1 tab:

@interface MyClass : NSObject {
    @private
    id _privateIvar;

    @protected
    id _protectedIvar;
}

Access specifiers should be declared explicitly

Property Declaration

Between @property and opening parentheses 1 space symbol should be used
Parameters ordering: atomic/nonatomic, memory policy, access specified (readonly/readwrite), setter declaration, getter declaration: @property (nonatomic, copy, readonly, getter=customGetter) NSString *value;

Protocol Declaration

@required and @optional aligned to the line beginning

Blocks / Closures Declaration

Code inside block / closure aligned by 1 tab
Opening and closing braces should be aligned by the first symbol of declaration:

dipatch_async(dispatch_get_main_queue(), ^{
    // your code here
});

NSArray *contentArray = nil;
[contentArray enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop){
     // your code here
}];

[UIView animateWithDuration:0.3 animations:^{
    // your code here
} completion:^(BOOL finished){
     // your code here
}];

There is no space between ^ and return type / arguments: ^(id response){} ^NSUInteger * (id response){}

Naming

In general we're using Apple Coding Guidelines for Cocoa with several highlights:

Three-letters prefix is REQUIRED
Methods for the non-project class categories should be prefixed by lowercasePrefix_: - (void)sch_performTask:(id)arg

Constants

Magical numbers are not allowed - constants should be used instead. Exception: constant value, used in local one place with descriptive name
No "raw" strings. Exception: the same as for the magical numbers
Desirable to use extern keyword:

// SCHNotifier.h
OBJC_EXTERN NSString * const SCHNotifierDidChangeStateNotification;
OBJC_EXTERN const CGFloat SCHDefaultAnimationDuration;

// SCHNotifier.m

NSString * const SCHNotifierDidChangeStateNotification = @"com.project.notifier.stateDidChange";
const CGFloat SCHDefaultAnimationDuration = 0.33;

Required / recommended best practices

Types Declaration / Usage

Use typedef for blocks declaration and custom enums / scalar types
Use NSInteger, NSTimeInterval, CGFloat, etc over plain types. Therefore it is easier to migrate to the 64-bits

Forward Declaration

Use forward declaration whenever possible

Ivars

@public ivars not allowed

Properties

Use copy specifier in case mutability leads to unexpected behaviour (i.e. when NSMutableString passed as NSString and mutated outside of the class)
Use readonly for public properties whenever possible to prevent unexpected class usage (i.e. outlet assigned from client code, etc)
(iOS only) Use nonatomic whenever possible to speedup code execution
Desirable to access underlying property's ivar only in init/setter/getter
Use of @property solely to create _ivar is not recommended and should be prohibited

Exceptions handling

Use exceptions only where it is required. Desirable to use NSError ** and / or return result status (i.e. Success, Fail)

Protocols

Delegate methods should always pass sender argument:

@protocol CustomClassDelegate <NSObject>

- (NSInteger)someDelegateMethod:(CustomClass *)customClass;
- (void)customClass:(CustomClass *)customClass didSelectRowAtIndexPath:(NSIndexPath *)indexPath;

@end

Protocol support for properties / vars should be declared explicitly: id<Protocol> instance = ...;, @property (nonatomic, weak) id<Protocol> delegate;

Boolean statements

Desirable to use implicit equality check: if (bar && baz && quux)

Preprocessor usage

Prefer c-functions / constants / methods over #define

AppDelegate

Keep your AppDelegate as clean as possible. Any logic, not related to AppDelegate (database seeding, networking, etc) is not allowed

Clean .pch

Group required #defines, constants to a separate header (SCHConstants.h, SCHDefines.h). Garbage in .pch is not allowed

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