Classy Methods

Objectives

Accomplish the same tasks using literals, instance methods, and class methods.

Instructions

Fork and clone this lab.

Open the objc-classy-methods.xcodeproj file. Navigate to FISAppDelegate.m and enter the following code-alongs into the application:didFinishLaunchingWithOptions: method.

Code-Along I: `NSString`

A. Use an Instance Method

Create a new NSString variable called katherine and use the string literal to set it to @"Katherine":

NSString *katherine = @"Katherine";

Create a new NSString variable called katherineHepburn and use it to capture the return of calling the stringByAppendingString: method on katherine with @" Hepburn" supplied as the argument string (don't forget the leading space):

NSString *katherineHepburn = [katherine stringByAppendingString:@" Hepburn"];

Use NSLog() to print katherineHepburn to the console:

NSLog(@"%@", katherineHepburn);

This should print: Katherine Hepburn.

B. Use an `init...` Method

Create a new NSString variable called james and use the string literal to set it to @"James":

NSString *james = @"James";

Create a new NSString variable called jamesStewart and set use it to capture the return of calling the alloc and initWithFormat: method pair on NSString. Supply the argument with a format string with two object specifiers (%@) separated by a single space, the james string as the first specified object, and @"Stewart" as the second specified object:

NSString *jamesStewart = [[NSString alloc] initWithFormat:@"%@ %@", james, @"Stewart"];

Use NSLog() to print jamesStewart to the console:

NSLog(@"%@", jamesStewart);

This should print: James Stewart.

C. Use a Class Method

Create a new NSString variable called queen and use the string literal to set it to @"Queen":

NSString *queen = @"Queen";

Create a new NSString variable called queenElizabethII and use it to capture the return of calling the stringWithFormat: class method called on NSString itself. Supply the argument with a format string with three object specifiers (%@) separated by a single space, the queen string as the first specified object, @"Elizabeth" as the second specified object, and the Roman numerals @"II" as the third specified object:

NSString *queenElizabethII = [NSString stringWithFormat:@"%@ %@ %@", queen, @"Elizabeth", @"II"];

Use NSLog() to print queenElizabethII to the console:

NSLog(@"%@", queenElizabethII);

This should print: Queen Elizabeth II.

Code-Along II: `NSArray`

A. Use the Array Literal

Create a new NSArray variable called classyThings and use the array literal to set it to an array containing the strings @"monocle", @"top hat", and @"martini glass":

NSArray *classyThings = @[ @"monocle", @"top hat", @"martini glass" ];

Use NSLog() to print classyThings to the console:

NSLog(@"%@", classyThings);

This should print:

(
    monocle,
    "top hat",
    "martini glass"
)

B. Use an Initializer Method

Create a new NSArray variable called classyPeople and use it to capture the return of calling the alloc and initWithObjects: method pair on NSArray. Supply the argument with a list of the three full-name string objects from Code-Along I, end the list with nil:

NSArray *classyPeople = [[NSArray alloc] initWithObjects:@"Katherine Hepburn", @"James Stewart", @"Queen Elizabeth II", nil];

Use NSLog() to print classyPeople to the console:

NSLog(@"%@", classyPeople);

This should print:

(
    "Katherine Hepburn",
    "James Stewart",
    "Queen Elizabeth II"
)

C. Use a Class Method

Create a new NSArray variable called classyDrinks and use it to capture the return of calling the arrayWithObjects: class method on NSArray itself. Supply the argument with a list of strings; @"Old Fashioned", @"Churchill Martini", @"Prosecco"; and end the list with nil:

NSArray *classyDrinks = [NSArray arrayWithObjects:@"Old Fashioned", @"Churchill Martini", @"Prosecco", nil];

Use NSLog() to print classyDrinks to the console:

NSLog(@"%@", classyDrinks);

This should print:

(
    "Old Fashioned",
    "Churchill Martini",
    Prosecco
)

Code-Along III: `NSDictionary`

A. Use the Dictionary Literal

1 — Create a new NSDictionary variable called classyByLiteral and use the dictionary literal to set it to a dictionary containing three keys; @"classy things", @"classy people", and @"classy drinks"; which each point to an empty array literal:

NSDictionary *classyByLiteral = @{ @"classy things" : @[],
                                   @"classy people" : @[],
                                   @"classy drinks" : @[]
                                   };

2 — Populate the value arrays with the following strings:

for @"classy things", populate its value array with @"monocle", @"top hat", and @"martini glass",
for @"classy people", populate its value array with @"Katherine Hepburn", @"James Stewart", and @"Queen Elizabeth II", and
for @"classy drinks", populate its value array with @"Old Fashioned", @"Churchill Martini", and @"Prosecco":

NSDictionary *classyByLiteral = @{ @"classy things" : @[ @"monocle"            ,
                                                         @"top hat"            ,
                                                         @"martini glass"      ],
                                   @"classy people" : @[ @"Katherine Hepburn"  ,
                                                         @"James Stewart"      ,
                                                         @"Queen Elizabeth II" ],
                                   @"classy drinks" : @[ @"Old Fashioned"      ,
                                                         @"Churchill Martini"  ,
                                                         @"Prosecco"           ]
                                   };

3 — Use NSLog() to print classyByLiteral to the console:

NSLog(@"%@", classyByLiteral);

This should print, in some order:

{
    "classy drinks" =     (
        "Old Fashioned",
        "Churchill Martini",
        Prosecco
    );
    "classy people" =     (
        "Katherine Hepburn",
        "James Stewart",
        "Queen Elizabeth II"
    );
    "classy things" =     (
        monocle,
        "top hat",
        "martini glass"
    );
}

B. Use an Initializer Method

Create a new NSDictionary variable called classyByInit and use to capture the return of calling the alloc and initWithObjectsAndKeys: method pair on NSDictionary. Use the array variables from Code-Along II to supply the argument with a list of the three arrays each followed by the associated key string to create a dictionary that matches the one above:

NSDictionary *classyByInit = [[NSDictionary alloc] initWithObjectsAndKeys:classyThings, @"classy things", classyPeople, @"classy people", classyDrinks, @"classy drinks", nil];
Top-tip: Be careful to list the "object" before the "key". This is inverted from the order of key : object when using the dictionary literal.

Use NSLog() to print classyByInit to the console:

NSLog(@"%@", classyByInit);

This should print a dictionary matching the one from section A. Verify that the keys and objects are not inverted:

// correct key : value order

{
    "classy drinks" =     (
        "Old Fashioned",
        "Churchill Martini",
        Prosecco
    );
    "classy people" =     (
        "Katherine Hepburn",
        "James Stewart",
        "Queen Elizabeth II"
    );
    "classy things" =     (
        monocle,
        "top hat",
        "martini glass"
    );
}

// incorrect key : value order

{
        (
        monocle,
        "top hat",
        "martini glass"
    ) = "classy things";
        (
        "Katherine Hepburn",
        "James Stewart",
        "Queen Elizabeth II"
    ) = "classy people";
        (
        "Old Fashioned",
        "Churchill Martini",
        Prosecco
    ) = "classy drinks";
}

C. Use a Class Method

1 — Create a new NSDictionary variable called classyByClass and use it to capture the return of calling the dictionaryWithObjects:forKeys: class method on NSDictionary itself. Supply the first argument with an array literal containing the three arrays from Code-Along II, and supply the second argument with an array containing the key string literals that match the keys used in sections A and B. Make sure to keep them in the correct order!:

NSDictionary *classyByClass = [NSDictionary dictionaryWithObjects:@[classyThings, classyPeople, classyDrinks]
                                                          forKeys:@[@"classy things", @"classy people", @"classy drinks"]];

2 — Use NSLog() to print classyByClass to the console:

NSLog(@"%@", classyByClass);

This should print another dictionary that matches the dictionaries from sections A and B:

{
    "classy drinks" =     (
        "Old Fashioned",
        "Churchill Martini",
        Prosecco
    );
    "classy people" =     (
        "Katherine Hepburn",
        "James Stewart",
        "Queen Elizabeth II"
    );
    "classy things" =     (
        monocle,
        "top hat",
        "martini glass"
    );
}

molgin/objc-classy-methods-000

Classy Methods

Objectives

Instructions

Code-Along I: NSString

A. Use an Instance Method

B. Use an init... Method

C. Use a Class Method

Code-Along II: NSArray

A. Use the Array Literal

B. Use an Initializer Method

C. Use a Class Method

Code-Along III: NSDictionary

A. Use the Dictionary Literal

B. Use an Initializer Method

C. Use a Class Method

Code-Along I: `NSString`

B. Use an `init...` Method

Code-Along II: `NSArray`

Code-Along III: `NSDictionary`