learn-objective-c-on-the-mac.markdown

Learn Objective-C on the Mac

by Mark Dalrymple and Scott Knaster

I, Michael Parker, own this book and took these notes to further my own learning. If you enjoy these notes, please purchase the book!

Chapter 2: Extensions to C

• pg 8: Files ending in .m are handled by the Objective-C compiler.
• pg 9: The #import directive is like #include, but doesn't require the programmer to use an #ifndef directive so that a file is included only once.
• pg 9: A framework is a collection of parts -- header files, libraries, images, sounds, and more -- collected together into a single unit.
• pg 10: Each framework has a master header file that includes all the framework's individual header files.
• pg 13: BOOL is just a type definition for the signed character type, where YES is 1 and NO is 0.
• pg 16: Don't compare a BOOL value directly to YES, as some methods might return values that assume that anything non-zero is treated as YES.

Chapter 3: Introduction to Object-Oriented Programming

• pg 39: id is a generic type that's used to refer to any kind of object; it's simply a pointer.
• pg 41: Each object has a reference to its class; when an object receives a message, the object delegates to its class, which finds and executes the correct code.
• pg 46: The argument type or return type in a method signature is always in parentheses.
• pg 47: If a method takes an argument, it has a colon; if it takes no arguments, it has no colons.
• pg 48: Defining a method solely in the @implementation directive does not make it private; the method is still accessible due to the language's dynamic nature.

Chapter 4: Inheritance

• pg 62: There is no support for multiple inheritance, but you can reap some of its benefits by using categories and protocols.
• pg 68: NSObject declares one instance variable, named isa, which holds the pointer to the object's class.
• pg 69: To fix the fragile base class problem, the 64-bit Objective-C runtime in Leopard use indirection for determining ivar locations instead of adding offsets to self.
• pg 70: To call the superclass version of a method, send an appropriate message to super.

Chapter 5: Composition

• pg 75: The description method in your class defines how it is printed by NSLog with the %@ format specifier.
• pg 76: Pointers are automatically initialized to nil (a zero value) when declared.
• pg 77: When a constructor calls its superclass constructor with [super init], it's convention to assign the result to self.
• pg 80: Getter methods shouldn't start with get; in Cocoa, this means the value is returned via a pointer passed in as an argument.

Chapter 6: Source File Organization

• pg 88: Using a .mm file as an extension tells the compiler you've written your code in Objective-C++, which allows using C++ and Objective-C together.
• pg 90: In Xcode, groups allow organizing files together but do not equate to directories on your hard drive.
• pg 92: In an #import statement, a header file in angle brackets is a read-only system header file, while one in quotes is local to your project.
• pg 95: A class is forward referenced with @class, which is put between the import statements and the @interface keyword.

Chapter 7: More About Xcode

• pg 106: When typing a class or method name, press the escape key to see all code completion options.
• pg 108: To move between placeholders after code completion, press Control and forward slash.
• pg 111: Edit all in Scope will allow renaming a local variable in a function, while the Refactor option allows renaming an entire class.
• pg 115: To search for classes, methods, or properties, press Command, Option, Shift, and D.
• pg 119: Comments with TODO:, FIXME:, !!!: and ???: are indexed automatically by the function menu.
• pg 120: The split box beneath the lock will horizontally split the window; holding Option will split the window vertically.
• pg 122: Holding Control and double-clicking on a symbol will issue a documentation seach for that symbol.
• pg 124: Disable a breakpoint by clicking on it symbol, or remove it by dragging the symbol out of the gutter.
• pg 129: Hold control and press period to cycle forward through code completion options; adding shift will cycle backward.

Chapter 8: A Quick Tour of the Foundation Kit

• pg 131: Cocoa is two different frameworks: Foundation and Application Kit, where the former has useful low-level, data-oriented classes and types.
• pg 135: Declaring a method with a plus sign makes it a class method.
• pg 136: The isEqualToString method of a NSString compares string values; using == will only compare the pointers.
• pg 141: Because inheritance works with class methods and instance methods, stringWithFormat is available on class NSMutableString.
• pg 143: A class name with CF means it's part of the Core Foundation framework and written in C; CF and Cocoa objects are "toll-free bridged," so they can be used interchangeably.
• pg 147: When NSEnumerator returns nil, iteration has finished, and so you can't store nil in arrays.
• pg 149: The initializer lists for both NSArray and NSDictionary have nil as their last value.
• pg 150: Extending NSString, NSArray, or NSDictionary is problematic because they're implemented as class clusters, or many classes behind a common interface.
• pg 152: NSValue allows putting structs into an NSArray or NSDictionary; the @encode compiler directive creates the required string describing the type for you.

Chapter 9: Memory Management

• pg 163: The retain method returns an id, so you can chain it with other messages.
• pg 167: If a setter method retains its argument and then releases its current value, it guards against the retain count hitting 0 when passing the current value as the argument.
• pg 169: An autorelease pool is created on an event, and destroyed when the event ends.
• pg 172: If you get a hold of an object in any way other than new, alloc, or copy, assume it has a retain count of 1 and has been autoreleased.
• pg 175: Autorelease pools are kept in a stack; sending an autorelease message puts the receiver into the topmost pool.
• pg 177: For iPhone programming, Apple recommends you avoid using autorelease in your own code, and convenience functions that give you autoreleased objects.

Chapter 10: Object Initialization

• pg 179: The alloc method initializes all memory to zero, all numbers as 0, all booleans as NO, and all pointers as nil.
• pg 181: If a new object is returned from a superclass init method, self must be updated so any subsequent instance variable references affect the right memory locations.
• pg 183: The init methods are ordinary methods that follow a naming convention; you can provide as many convenience initializers as needed.
• pg 198: All initializer methods of a class use the designated initializer to do initialization work, and subclasses use the superclass' designated initializer as well.

Chapter 11: Properties

• pg 205: The @property keyword in the header file includes the type, while the @synthesize keyword does not.
• pg 208: Always specify copy in properties for string attributes; a common error is to use a string from a UI component, which are mutable and change as the user types.
• pg 212: A default decoration for the @property keyword is assign; alternatively you can use retain or copy.
• pg 213: Passing nil to a setter generated from the property will release the previous value if needed.

Chapter 12: Categories

• pg 226: Using categories you can split a class' implementation across multiple files, and even among frameworks.
• pg 227: To simulate a private method, exclude it from the .h file, and add it to a category at the top of the implementation file while leaving the definition in the header's @implementation part.

Chapter 13: Protocols

• pg 235: You adopt a protocol by listing its name in your class' interface declaration; then your class conforms to the protocol.
• pg 239: When implementing copyWithZone, send the allocWithZone message to [self class] to create a class of the right subtype.
• pg 242: A copyWithZone method should send a copyWithZone message to its parent class if available, but send a copy message to objects that compose it.
• pg 246: Specifying protocol names on instance variables and methods arguments ensures that the assigned variables conform to those protocols.

Chapter 14: Introduction to the AppKit

• pg 252: IBOutlet is defined to be nothing, so it disappears upon compiling; IBAction is defined to be void, and so the associated method returns nothing.
• pg 253: Nib files, which stands for NeXT Interface Builder, are binary files that serialize objects, and .xib files are XML that are compiled into nib files.
• pg 260: When making connections in Interface Builder, drag from the object that needs to know something to the object it needs to know about.
• pg 262: When an object recreated from a nib file is initialized, all its IBOutlet instances are nil; you must wait until awakeFromNib is called to do any work with them.

Chapter 15: File Loading and Saving

• pg 266: NSTimeInterval is simply a typedef of double representing some interval of seconds.
• pg 268: Property list files can be converted between XML and compressed binary format using the plutil command.
• pg 270: The NSCoder class allows for converting objects to NSData and back; NSData, along with NSArray, NSDictionary, NSString, NSNumber, and NSDate, can be used in property lists.
• pg 273: If a parent class adopts NSCoding, initWithCoder should call the superclass implementation of initWithCoder first; otherwise, simply call init.

Chapter 16: Key-Value Coding

• pg 280: KVC automatically boxes and unboxes scalar values into NSValue or NSNumber when neccessary.
• pg 281: Methods like valueForKey and setValue:forKey will use getters and setters if they exist, and will access the variables directly otherwise.
• pg 283: If a key path includes an array or to-many attribute, the remaining part of the key is sent to every object in the array, and the values are returned in an array.
• pg 288: KVC operators are always used with valueForKeyPath.
• pg 294: When printing, "<null>" is the [NSNull null] object which could be returned as a value from a NSDictionary, while "(null)" is nil and could mean the key did not exist.

Chapter 17: NSPredicate

• pg 301: You cannot use $VARIABLE for key paths in a NSPredictate string, only values; use the %K format specifier to substitute key paths.
• pg 303: Curly braces denote an array, even though they are printed as having parentheses.
• pg 305: String relational operators can be decorated with [c] for case-insensitivity, and [d] for diacritic-insensitivity (i.e. removing accents), or both.