Objective-C Cheat Sheet

Fundamental Objective-C syntax covering classes, properties, messaging, ARC memory management, and protocols.

2 PagesIntermediateApr 12, 2026

Hello World

A minimal Objective-C program.

objectivec

#import <Foundation/Foundation.h>int main(int argc, const char * argv[]) {    @autoreleasepool {        NSString *greeting = @"Hello, World!";        NSLog(@"%@", greeting);    }    return 0;}

Interface & Implementation

Declaring a class with properties and methods.

objectivec

// Person.h@interface Person : NSObject@property (nonatomic, strong) NSString *name;@property (nonatomic, assign) NSInteger age;- (instancetype)initWithName:(NSString *)name age:(NSInteger)age;- (void)sayHello;@end// Person.m@implementation Person- (instancetype)initWithName:(NSString *)name age:(NSInteger)age {    self = [super init];    if (self) {        _name = name;        _age = age;    }    return self;}- (void)sayHello {    NSLog(@"Hi, I'm %@", self.name);}@end

Properties & Messaging

Core object and messaging syntax.

[obj method]- Square-bracket message send syntax
@property (nonatomic, strong)- Declares an object property, auto-synthesizes getter/setter
self / super- Reference to the current instance / the superclass
nil- Null object pointer; messaging nil is a safe no-op
[[Person alloc] init]- Allocate memory, then initialize an instance
id- Generic object pointer type, any Objective-C object

Memory Management (ARC)

Automatic Reference Counting basics.

ARC- Automatic Reference Counting; the compiler inserts retain/release calls for you
strong- Owns the referenced object, keeps it alive
weak- Non-owning reference, automatically becomes nil when the object is deallocated
retain/release- Managed automatically under ARC; do not call manually in ARC code
@autoreleasepool- Block that drains autoreleased objects at its end

Protocols

Defining and conforming to a protocol.

objectivec

@protocol Greetable <NSObject>- (void)greet;@optional- (void)farewell;@end@interface Robot : NSObject <Greetable>@end@implementation Robot- (void)greet {    NSLog(@"Beep boop, hello!");}@end

Pro Tip

Prefer weak references for delegate properties (@property (nonatomic, weak) id<Delegate> delegate;) to avoid retain cycles between parent and child objects.

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