Introduction to Objective-C and Cocoa Touch

Informal introduction to Objective-C/Cocoa Touch given to Tumblr engineering

Transcript

1. Introduction to Objective-C
   and Cocoa Touch
   Bryan Irace
   

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2. I. Language
   

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3. “A superset of the C programming
   language and provides object-
   oriented capabilities and a
   dynamic runtime”
   • Inherits C syntax, primitives, flow control
   • Adds syntax for classes, methods, object literals
   • Dynamically typed, defers a lot to runtime
   

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4. Classes have separate header and
   implementation files
   !
   Header files declare a class’s “public” interface
   Class definitions
   

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5. // Import individual classes, or in this case, a whole framework
   #import
   !
   // Prefixed class name (no namespaces ) : superclass
   @interface BRYCalculator : NSObject
   !
   // Instance method with two arguments
   - (NSInteger)add:(NSInteger)number1 toNumber:(NSInteger)number2;
   !
   // Class method ("static" to you Java folk)
   + (void)initialize;
   !
   @end
   

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6. You don’t “invoke methods,” you “send
   messages.”
   !
   It’s kind of the same thing except any message
   can be sent to any object. More on this later.
   Message sending
   

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7. !
   [object doSomething];
   [object doSomethingWithObject:someArgument
   anotherObject:otherArgument];
   !
   [BRYObject initialize];
   

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8. NSString *string = nil;
   !
   // Won't crash
   [string description];
   !
   // Will return `NO`
   BOOL stringIsHTMLFileName = [string hasSuffix:@".html"];
   

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9. Properties are used to encapsulate your data.
   Accessor methods are created for you by the compiler.
   !
   Should pretty much always use them instead of direct
   instance variables.
   Properties
   

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10. @property (nonatomic, copy) NSString *firstName;
    !
    @property (nonatomic, copy) NSString *lastName;
    !
    @property (nonatomic, readonly) NSString *fullName;
    !
    @property (nonatomic, getter = isTumblrEmployee) BOOL tumblrEmployee;
    

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11. “Used to declare methods and properties that are
    independent of any specific class"
    Protocols
    

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12. // Protocols can extend other protocols
    @protocol TMTheming
    !
    !
    - (void)updateTheme:(TMTheme *)theme;
    !
    !
    @optional
    !
    !
    - (void)someOptionalMethod;
    !
    @end
    

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13. Add methods to existing classes
    Categories
    

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14. @interface NSArray (TumblrAdditions)
    !
    - (BOOL)isEmpty;
    !
    - (BOOL)isNotEmpty;
    !
    @end
    

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15. Lambdas, closures, whatever you call them
    Blocks
    

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16. view.alpha = 1;
    !
    [UIView animateWithDuration:0.2 animations:^{
    view.alpha = 0;
    }];
    !
    !
    !
    !
    NSArray *array = @[@0, @2, @3, @4, @5];
    !
    array = [array filteredArrayUsingBlock:^BOOL (NSNumber *number) {{
    return [number unsignedIntegerValue] % 2 == 0;
    }];
    

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17. Thankfully we no longer need to manually allocate and release memory (unless
    using C APIs)
    !
    Still need to be careful to not create retain cycles though
    Memory management
    

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18. BRYObject *object = [BRYObject new];
    BRYObject *otherObject = [[BRYObject alloc] init];
    object.childObject = otherObject;
    otherObject.childObject = object;
    !
    // Prevent a retain cycle by using a "weak reference"
    @property (nonatomic, weak) NSObject *childObject;
    

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19. II. SDK
    

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20. Comprised of numerous frameworks
    (Foundation, UIKit, TextKit, Core
    Data, AVFoundation, etc.)
    Cocoa Touch
    

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21. Singleton that allows you to handle application lifecycle events
    !
    • Application launches
    • Foreground/background
    • Push notifications
    • Inter-app communication
    App delegate
    

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22. Base class for almost all views
    !
    • Has a “frame” (coordinates and size), determines where it shows up on
    screen
    • Frame can be set manually or via constraints (AutoLayout)
    • Has an array of “subviews” (forming a hierarchy)
    • Can be configured in code or in Interface Builder
    UIView
    

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23. Generally one controller visible on screen at a time
    !
    • Provides hooks like “viewWillAppear”, “viewWillDisappear”, rotation
    • View controllers can have children
    • Can implement “container view controllers” (e.g. tab bar,
    navigation bar)
    UIViewController
    

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24. • Core Data: persistent object graph
    • SQLite
    • NSCoding: simple object serialization
    • User defaults: key/value preference store
    • Keychain: secure, encrypted container
    Persistence
    

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25. // `self` will be notified when the scroll view’s content offset changes
    [scrollView addObserver:self forKeyPath:@“contentOffset”];
    !
    // `[self wipeDatabase:]` will be called when notification is posted
    [[NSNotificationCenter defaultCenter] addObserver:self
    selector:@selector(wipeDatabase:)
    name:@"UserDidLogoutNotification"];
    Observing changes
    

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26. NSOperationQueue *queue = [[NSOperationQueue alloc] init];
    queue.maxConcurrentOperationCount = 2;
    !
    [queue addOperationWithBlock:^{
    // Do something on a background thread
    [[NSOperationQueue mainQueue] addOperationWithBlock:^{
    // Update the UI on the main thread
    }];
    }];
    Concurrency
    

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27. III. Demo
    

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28. IV. Runtime
    

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29. Can specify which objects respond to which
    selectors at runtime
    !
    Can kind of simulate multiple inheritance this way
    Dynamic method resolution
    

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30. SEL originalSelector = NSSelectorFromString(@"signRequest:withParameters:");
    SEL newSelector = NSSelectorFromString(@"addHeadersAndSignRequest:withParameters:");
    !
    Method originalMethod = class_getInstanceMethod(class, originalSelector);
    Method newMethod = class_getInstanceMethod(class, newSelector);
    method_exchangeImplementations(originalMethod, newMethod);
    !
    - (void)addHeadersAndSignRequest:(NSMutableURLRequest *)request
    withParameters:(NSDictionary *)parameters {
    // TODO: Add headers to request
    // Call original method by sending *new* message (because we swapped them,
    remember?)
    [self addHeadersAndSignRequest:request withParameters:parameters];
    }
    Swizzling
    

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31. Add state to objects without subclassing
    !
    objc_setAssociatedObject(self, UIViewShakeInitialFrameKey, self.frame,
    OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    self.frame = objc_getAssociatedObject(self, UIViewShakeInitialFrameKey);
    Associated objects
    

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32. V. Tooling
    

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33. Instruments
    

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