thebushidocollective/han/objc-protocols-categories

// Basic protocol declaration
@protocol Drawable <NSObject>
@required
- (void)draw;
- (CGRect)bounds;
 
@optional
- (void)drawWithStyle:(NSString *)style;
@end
 
// Protocol adoption in interface
@interface Circle : NSObject <Drawable>
@property (nonatomic, assign) CGFloat radius;
@property (nonatomic, assign) CGPoint center;
@end
 
@implementation Circle
 
- (void)draw {
    NSLog(@"Drawing circle at (%.1f, %.1f) with radius %.1f",
          self.center.x, self.center.y, self.radius);
}
 
- (CGRect)bounds {
    return CGRectMake(
        self.center.x - self.radius,
        self.center.y - self.radius,
        self.radius * 2,
        self.radius * 2
    );
}
 
@end
 
// Multiple protocol adoption
@protocol Movable <NSObject>
- (void)moveToPoint:(CGPoint)point;
- (CGPoint)currentPosition;
@end
 
@protocol Scalable <NSObject>
- (void)scaleBy:(CGFloat)factor;
- (CGFloat)currentScale;
@end
 
@interface Shape : NSObject <Drawable, Movable, Scalable>
@property (nonatomic, assign) CGPoint position;
@property (nonatomic, assign) CGFloat scale;
@end
 
@implementation Shape
 
- (void)draw {
    NSLog(@"Drawing shape");
}
 
- (CGRect)bounds {
    return CGRectZero;
}
 
- (void)moveToPoint:(CGPoint)point {
    self.position = point;
}
 
- (CGPoint)currentPosition {
    return self.position;
}
 
- (void)scaleBy:(CGFloat)factor {
    self.scale *= factor;
}
 
- (CGFloat)currentScale {
    return self.scale;
}
 
@end
 
// Protocol as type
void drawShapes(NSArray<id<Drawable>> *shapes) {
    for (id<Drawable> shape in shapes) {
        [shape draw];
        NSLog(@"Bounds: %@", NSStringFromCGRect([shape bounds]));
    }
}
 
// Checking protocol conformance
void checkConformance(id object) {
    if ([object conformsToProtocol:@protocol(Drawable)]) {
        id<Drawable> drawable = object;
        [drawable draw];
    }
}
 
// Protocol inheritance
@protocol AdvancedDrawable <Drawable>
- (void)drawWithTransform:(CGAffineTransform)transform;
- (void)drawWithBlendMode:(CGBlendMode)blendMode;
@end
 
@interface AdvancedShape : NSObject <AdvancedDrawable>
@end
 
@implementation AdvancedShape
 
- (void)draw {
    NSLog(@"Advanced drawing");
}
 
- (CGRect)bounds {
    return CGRectZero;
}
 
- (void)drawWithTransform:(CGAffineTransform)transform {
    NSLog(@"Drawing with transform");
}
 
- (void)drawWithBlendMode:(CGBlendMode)blendMode {
    NSLog(@"Drawing with blend mode");
}
 
@end

// Protocol with optional methods
@protocol DataSourceDelegate <NSObject>
 
@required
- (NSInteger)numberOfItems;
 
@optional
- (NSString *)titleForItemAtIndex:(NSInteger)index;
- (UIImage *)imageForItemAtIndex:(NSInteger)index;
- (void)didSelectItemAtIndex:(NSInteger)index;
 
@end
 
// Implementing partial optional methods
@interface ListView : UIView <DataSourceDelegate>
@property (nonatomic, weak) id<DataSourceDelegate> dataSource;
@end
 
@implementation ListView
 
- (void)reloadData {
    NSInteger count = [self.dataSource numberOfItems];
 
    for (NSInteger i = 0; i < count; i++) {
        // Check if optional method is implemented
        if ([self.dataSource respondsToSelector:
            @selector(titleForItemAtIndex:)]) {
            NSString *title = [self.dataSource titleForItemAtIndex:i];
            NSLog(@"Title: %@", title);
        }
 
        if ([self.dataSource respondsToSelector:
            @selector(imageForItemAtIndex:)]) {
            UIImage *image = [self.dataSource imageForItemAtIndex:i];
            NSLog(@"Image: %@", image);
        }
    }
}
 
// Required method implementation
- (NSInteger)numberOfItems {
    return 0;
}
 
@end
 
// Selective implementation in adopter
@interface SimpleDataSource : NSObject <DataSourceDelegate>
@end
 
@implementation SimpleDataSource
 
- (NSInteger)numberOfItems {
    return 10;
}
 
- (NSString *)titleForItemAtIndex:(NSInteger)index {
    return [NSString stringWithFormat:@"Item %ld", (long)index];
}
 
// imageForItemAtIndex: not implemented
 
@end
 
// Delegate pattern with optional methods
@protocol ViewControllerDelegate <NSObject>
 
@optional
- (void)viewControllerWillAppear:(UIViewController *)controller;
- (void)viewControllerDidAppear:(UIViewController *)controller;
- (void)viewControllerWillDisappear:(UIViewController *)controller;
- (void)viewControllerDidDisappear:(UIViewController *)controller;
 
@end
 
@interface CustomViewController : UIViewController
@property (nonatomic, weak) id<ViewControllerDelegate> delegate;
@end
 
@implementation CustomViewController
 
- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];
 
    if ([self.delegate respondsToSelector:
        @selector(viewControllerWillAppear:)]) {
        [self.delegate viewControllerWillAppear:self];
    }
}
 
- (void)viewDidAppear:(BOOL)animated {
    [super viewDidAppear:animated];
 
    if ([self.delegate respondsToSelector:@selector(viewControllerDidAppear:)]) {
        [self.delegate viewControllerDidAppear:self];
    }
}
 
@end
 
// Property requirements in protocols
@protocol Identifiable <NSObject>
 
@required
@property (nonatomic, readonly) NSString *identifier;
@property (nonatomic, strong) NSString *name;
 
@optional
@property (nonatomic, strong) NSDictionary *metadata;
 
@end
 
@interface User : NSObject <Identifiable>
@end
 
@implementation User
 
@synthesize identifier = _identifier;
@synthesize name = _name;
// metadata not implemented (optional)
 
@end

// Basic category
@interface NSString (Validation)
- (BOOL)isValidEmail;
- (BOOL)isValidPhoneNumber;
- (NSString *)trimmedString;
@end
 
@implementation NSString (Validation)
 
- (BOOL)isValidEmail {
    NSString *emailRegex =
        @"[A-Z0-9a-z._%+-]+@[A-Za-z0-9.-]+\\.[A-Za-z]{2,}";
    NSPredicate *predicate = [NSPredicate predicateWithFormat:
        @"SELF MATCHES %@", emailRegex];
    return [predicate evaluateWithObject:self];
}
 
- (BOOL)isValidPhoneNumber {
    NSString *phoneRegex = @"^\\d{3}-\\d{3}-\\d{4}$";
    NSPredicate *predicate = [NSPredicate predicateWithFormat:
        @"SELF MATCHES %@", phoneRegex];
    return [predicate evaluateWithObject:self];
}
 
- (NSString *)trimmedString {
    return [self stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];
}
 
@end
 
// Using category methods
void categoryExample(void) {
    NSString *email = @"user@example.com";
    if ([email isValidEmail]) {
        NSLog(@"Valid email");
    }
 
    NSString *text = @"  Hello World  ";
    NSString *trimmed = [text trimmedString];
    NSLog(@"Trimmed: '%@'", trimmed);
}
 
// Category for code organization
@interface DataManager : NSObject
- (void)saveData:(NSData *)data;
- (NSData *)loadData;
@end
 
// Split functionality across categories
@interface DataManager (NetworkSync)
- (void)syncToServer;
- (void)downloadFromServer;
@end
 
@interface DataManager (LocalStorage)
- (void)saveToUserDefaults:(NSDictionary *)data;
- (NSDictionary *)loadFromUserDefaults;
@end
 
@implementation DataManager
 
- (void)saveData:(NSData *)data {
    NSLog(@"Saving data");
}
 
- (NSData *)loadData {
    return [NSData data];
}
 
@end
 
@implementation DataManager (NetworkSync)
 
- (void)syncToServer {
    NSLog(@"Syncing to server");
}
 
- (void)downloadFromServer {
    NSLog(@"Downloading from server");
}
 
@end
 
@implementation DataManager (LocalStorage)
 
- (void)saveToUserDefaults:(NSDictionary *)data {
    [[NSUserDefaults standardUserDefaults] setObject:data forKey:@"data"];
}
 
- (NSDictionary *)loadFromUserDefaults {
    return [[NSUserDefaults standardUserDefaults] dictionaryForKey:@"data"];
}
 
@end
 
// Category on UIKit classes
@interface UIColor (CustomColors)
+ (UIColor *)brandPrimaryColor;
+ (UIColor *)brandSecondaryColor;
@end
 
@implementation UIColor (CustomColors)
 
+ (UIColor *)brandPrimaryColor {
    return [UIColor colorWithRed:0.2 green:0.4 blue:0.8 alpha:1.0];
}
 
+ (UIColor *)brandSecondaryColor {
    return [UIColor colorWithRed:0.8 green:0.4 blue:0.2 alpha:1.0];
}
 
@end
 
// Using custom colors
void customColorExample(void) {
    UIView *view = [[UIView alloc] init];
    view.backgroundColor = [UIColor brandPrimaryColor];
}
 
// Category with associated objects
#import <objc/runtime.h>
 
@interface UIViewController (CustomProperty)
@property (nonatomic, strong) NSString *customIdentifier;
@end
 
@implementation UIViewController (CustomProperty)
 
- (NSString *)customIdentifier {
    return objc_getAssociatedObject(self, @selector(customIdentifier));
}
 
- (void)setCustomIdentifier:(NSString *)customIdentifier {
    objc_setAssociatedObject(
        self,
        @selector(customIdentifier),
        customIdentifier,
        OBJC_ASSOCIATION_RETAIN_NONATOMIC
    );
}
 
@end

// Public interface
@interface Person : NSObject
@property (nonatomic, strong, readonly) NSString *name;
@property (nonatomic, assign, readonly) NSInteger age;
 
- (instancetype)initWithName:(NSString *)name age:(NSInteger)age;
- (NSString *)description;
@end
 
// Class extension (private interface)
@interface Person ()
// Make readonly properties readwrite internally
@property (nonatomic, strong, readwrite) NSString *name;
@property (nonatomic, assign, readwrite) NSInteger age;
 
// Private properties
@property (nonatomic, strong) NSString *internalID;
@property (nonatomic, strong) NSMutableArray *privateData;
 
// Private methods
- (void)validateData;
- (void)logAccess;
@end
 
@implementation Person
 
- (instancetype)initWithName:(NSString *)name age:(NSInteger)age {
    self = [super init];
    if (self) {
        self.name = name;
        self.age = age;
        self.internalID = [[NSUUID UUID] UUIDString];
        self.privateData = [NSMutableArray array];
        [self validateData];
    }
    return self;
}
 
- (NSString *)description {
    [self logAccess];
    return [NSString stringWithFormat:@"%@ (%ld)", self.name, (long)self.age];
}
 
// Private method implementations
- (void)validateData {
    NSAssert(self.name.length > 0, @"Name must not be empty");
    NSAssert(self.age >= 0, @"Age must be non-negative");
}
 
- (void)logAccess {
    NSLog(@"Accessed person: %@", self.internalID);
}
 
@end