CodeToLive

Cocoa & Cocoa Touch in Objective-C

Cocoa (macOS) and Cocoa Touch (iOS) are the application frameworks that provide the core infrastructure for building Mac and iOS apps.

Core Architecture

Model-View-Controller (MVC)

// Model
@interface Task : NSObject
@property (nonatomic, copy) NSString *title;
@property (nonatomic) BOOL completed;
@end

// View Controller
@interface TaskViewController : UIViewController
@property (weak, nonatomic) IBOutlet UILabel *titleLabel;
@property (weak, nonatomic) IBOutlet UIButton *completeButton;
@property (strong, nonatomic) Task *task;

- (IBAction)completeButtonTapped:(id)sender;
@end

@implementation TaskViewController
- (void)viewDidLoad {
    [super viewDidLoad];
    self.titleLabel.text = self.task.title;
    [self updateCompleteButton];
}

- (void)updateCompleteButton {
    NSString *title = self.task.completed ? @"Completed" : @"Mark Complete";
    [self.completeButton setTitle:title forState:UIControlStateNormal];
}

- (IBAction)completeButtonTapped:(id)sender {
    self.task.completed = !self.task.completed;
    [self updateCompleteButton];
}
@end
            

Key Frameworks

Application Lifecycle

iOS App Lifecycle

// AppDelegate.h
@interface AppDelegate : UIResponder <UIApplicationDelegate>
@property (strong, nonatomic) UIWindow *window;
@end

// AppDelegate.m
@implementation AppDelegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    // App launched
    return YES;
}

- (void)applicationDidBecomeActive:(UIApplication *)application {
    // App became active
}

- (void)applicationWillResignActive:(UIApplication *)application {
    // App will become inactive
}

- (void)applicationDidEnterBackground:(UIApplication *)application {
    // App entered background
}

- (void)applicationWillEnterForeground:(UIApplication *)application {
    // App will enter foreground
}

- (void)applicationWillTerminate:(UIApplication *)application {
    // App will terminate
}
@end
            

macOS App Lifecycle

// AppDelegate.h
@interface AppDelegate : NSObject <NSApplicationDelegate>
@property (strong, nonatomic) NSWindow *window;
@end

// AppDelegate.m
@implementation AppDelegate

- (void)applicationDidFinishLaunching:(NSNotification *)notification {
    // App launched
}

- (void)applicationWillTerminate:(NSNotification *)notification {
    // App will terminate
}

- (BOOL)applicationShouldTerminateAfterLastWindowClosed:(NSApplication *)sender {
    return YES; // Quit when last window closed
}
@end
            

User Interface Components

Creating UI Programmatically

// Creating a button programmatically
UIButton *button = [UIButton buttonWithType:UIButtonTypeSystem];
button.frame = CGRectMake(20, 50, 280, 44);
[button setTitle:@"Tap Me" forState:UIControlStateNormal];
[button addTarget:self 
           action:@selector(buttonTapped:)
 forControlEvents:UIControlEventTouchUpInside];
[self.view addSubview:button];

// Creating a view controller
UIViewController *vc = [[UIViewController alloc] init];
vc.view.backgroundColor = [UIColor whiteColor];
UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(20, 100, 280, 30)];
label.text = @"Hello World";
[vc.view addSubview:label];
            

Using Storyboards and XIBs

// Loading from storyboard
UIStoryboard *storyboard = [UIStoryboard storyboardWithName:@"Main" bundle:nil];
UIViewController *vc = [storyboard instantiateViewControllerWithIdentifier:@"DetailVC"];

// Loading from XIB
CustomView *view = [[[NSBundle mainBundle] loadNibNamed:@"CustomView" owner:self options:nil] firstObject];
            

Event Handling

// Target-action pattern
UIButton *button = [UIButton buttonWithType:UIButtonTypeSystem];
[button addTarget:self 
           action:@selector(buttonTapped:)
 forControlEvents:UIControlEventTouchUpInside];

// Gesture recognizers
UITapGestureRecognizer *tap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(handleTap:)];
[self.view addGestureRecognizer:tap];

// Delegation
@interface MyViewController : UIViewController <UITextFieldDelegate>
@end

@implementation MyViewController
- (void)viewDidLoad {
    [super viewDidLoad];
    self.textField.delegate = self;
}

- (BOOL)textFieldShouldReturn:(UITextField *)textField {
    [textField resignFirstResponder];
    return YES;
}
@end
            

Core Data

// Core Data stack setup
@interface AppDelegate ()
@property (readonly, strong) NSPersistentContainer *persistentContainer;
@end

@implementation AppDelegate
- (NSPersistentContainer *)persistentContainer {
    if (_persistentContainer == nil) {
        _persistentContainer = [[NSPersistentContainer alloc] initWithName:@"Model"];
        [_persistentContainer loadPersistentStoresWithCompletionHandler:^(NSPersistentStoreDescription *storeDescription, NSError *error) {
            if (error != nil) {
                NSLog(@"Unresolved error %@, %@", error, error.userInfo);
                abort();
            }
        }];
    }
    return _persistentContainer;
}
@end

// Creating and saving objects
NSManagedObjectContext *context = self.persistentContainer.viewContext;
Person *person = [NSEntityDescription insertNewObjectForEntityForName:@"Person" inManagedObjectContext:context];
person.name = @"John";
person.age = 30;

NSError *error = nil;
if (![context save:&error]) {
    NSLog(@"Error saving context: %@", error);
}

// Fetching objects
NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"Person"];
fetchRequest.predicate = [NSPredicate predicateWithFormat:@"age > %@", @25];
NSSortDescriptor *sortDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"name" ascending:YES];
fetchRequest.sortDescriptors = @[sortDescriptor];

NSArray *people = [context executeFetchRequest:fetchRequest error:&error];
            

Networking

// URLSession data task
NSURL *url = [NSURL URLWithString:@"https://api.example.com/data"];
NSURLRequest *request = [NSURLRequest requestWithURL:url];

NSURLSessionDataTask *task = [[NSURLSession sharedSession] dataTaskWithRequest:request completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
    if (error) {
        NSLog(@"Error: %@", error);
        return;
    }
    
    NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *)response;
    if (httpResponse.statusCode == 200) {
        NSError *jsonError;
        NSDictionary *json = [NSJSONSerialization JSONObjectWithData:data options:0 error:&jsonError];
        if (!jsonError) {
            dispatch_async(dispatch_get_main_queue(), ^{
                // Update UI with json data
            });
        }
    }
}];
[task resume];
            

Best Practices

• Follow MVC pattern but be aware of Massive View Controller problem
• Use storyboards for simple flows and XIBs for reusable components
• Keep business logic out of view controllers when possible
• Use dependency injection for better testability
• Perform heavy operations on background threads
• Always update UI on main thread
• Use Auto Layout for responsive interfaces
• Follow Apple's Human Interface Guidelines