lecture 2：more Objective-C and Demo

这一课新建了几个其他的类以及在做出了第一个小demo

objectivec#import <Foundation/Foundation.h> #import "Card.h"  @interface Deck : NSObject  - (void)addCard:(Card *)card atTop:(BOOL)atTop; - (void)addCard:(Card *)card;  - (Card *)drawRandomCard;  @end  

老爷爷讲希望能够“通用化”自己建的一些类，比如card，比如deck所以这里的card，deck不仅仅能用于纸牌

比如我以后要做一个塔罗牌游戏也可以用同样的card deck类

1. Obj-C中没有默认参数的概念，也没有方法重载的概念，所以addCard因为参数不同，必须定义两次，但实际implement当然可以借助另一个
2. Deck是由card组成的，所以当然要import card，更何况方法都是针对card的

Deck的实现方法

objectivec#import "Deck.h" @interface Deck () @property (strong, nonatomic) NSMutableArray *cards;// of Card  @end @implementation Deck - (NSMutableArray *)cards {  if (!_cards) _cards = [[NSMutableArray alloc]init];  return _cards; } - (void)addCard:(Card *)card atTop:(BOOL)atTop{  if (atTop) {   [self.cards insertObject:card atIndex:0];  } else {   [self.cards addObject:card];  } } -(void)addCard:(Card *)card{  [self addCard:card atTop:NO]; } - (Card *)drawRandomCard{  Card *randomCard = nil;  if ([self.cards count]) {   unsigned index = arc4random() % [self.cards count];   randomCard = self.cards[index];   [self.cards removeObjectAtIndex:index];  }  return randomCard; } @end  

1. 注意少一个参数的addCard是如何巧妙的使用多一个参数的addCard Method的
2. 因为需要存储card，Array再度出现，但是NSMutableArray,需要具有Mutable的特性
3. 定义了cards只是定义了pointer，并没有allocate heap，所以有多么巧妙的lazy instantiation，_cards一开始只是nil，然后如果它是nil，我们就[[NSMutableArray alloc]init],，这是一个getter，于是我们首次去调用self.cards的时候它就会帮我们alloc和init，然后就不用怕cards是nil，因为消息是可以发送给nil的（如果不采取这样的措施cards始终是nil？反正就是会出错）
4. 注意这里的语法[self.cards insertObject:card atIndex:0]
5. 注意这一篇的代码中用了各种个样的保护措施，比如- (NSMutableArray *)cards中的if和- (Card *)drawRandomCard中的if

objectivec//Playingcard.h #import "Card.h"  @interface PlayingCard : Card  @property (strong, nonatomic) NSString *suit; @property (nonatomic) NSUInteger rank; + (NSArray *)validSuits; + (NSUInteger)maxRank; + (NSArray *)rankStrings;  @end  

1. PlayingCard是Card的子类，@interface处可看出
2. 使用NSUInteger或unsigned int是习惯问题，还是跟着老师走吧，同样，没有*号，因为不是object
3. 出现了类的method，所以是+，并且声明在public interface

objectivec//PlayingCard.m #import "PlayingCard.h" @implementation PlayingCard - (NSString *) contents {  NSArray *rankStrings = [PlayingCard rankStrings];  return [rankStrings[self.rank] stringByAppendingString:self.suit]; } @synthesize suit = _suit;// because we provide setter AND getter + (NSArray *)validSuits {  return @[@"♠︎",@"♣︎",@"♥︎",@"♦︎"]; } - (void)setSuit:(NSString *)suit {  if ([[PlayingCard validSuits] containsObject: suit]) {   _suit = suit;  } } - (NSString *)suit {  return _suit ? _suit : @"?"; } + (NSArray *)rankStrings {  return @[@"?",@"A",@"2",@"3",@"4",@"5",@"6",@"7",@"8",@"9",@10,@"J",@"Q",@"K"]; } + (NSUInteger)maxRank{ return [[self rankStrings] count]- 1; } - (void)setRank:(NSUInteger)rank {  if (rank <= [PlayingCard maxRank]) {   _rank = rank;  } } @end  

这一段简直是信息量无穷，复制粘贴，磕磕碰碰最终的PlayingCard.m看起来很简洁又好看，信息量太大，我只能随手抓一点：

1. @[...]用来做Array
2. @synthesize suit= _suit；出现是因为我们给了这个property的setter getter method，setter是setSuit，getter是suit
3. 调用一个类的method也用类名字，比如值得注意的是这里用[PlayingCard rankStrings]而非[self rankStrings]
4. 三目运算符 / stringByAppendingString method / dot.运算符，信息量.......

objectivec//PlayingCardDeck.h #import "Deck.h" @interface PlayingCardDeck : Deck @end 

最后出现的这一个类是真实的包含52张牌的PlayingCardDeck,Deck的子类

objectivec//PlayingCardDeck.m #import "PlayingCardDeck.h" #import "PlayingCard.h" @implementation PlayingCardDeck -(instancetype)init {  self = [super init];  if (self) {   for (NSString *suit in [PlayingCard validSuits]) {    for (NSUInteger rank = 1; rank <= [PlayingCard maxRank]; rank++) {     PlayingCard * card = [[PlayingCard alloc]init];     card.rank = rank;     card.suit = suit;     [self addCard:card];    }   }  }  return self; } @end  

同样，信息量很大

1. "instancetype " tells the compiler that this method returns an object which will be the same type as the object that this message was sent to.
2. self = [super init] return self同样是保护措施
3. 用循序造出了4*13张牌，同时把他们都add到了自身，也就是自己这个deck中
4. 记得这是deck的子类，所以addCard drawRandomCard都继续可用

一堂课真的很大的信息量，假装理清楚几个类之间的关系了

Card Deck是通用类PlayingCard PlayingCardDeck是针对这个游戏的具体类

Demo非常的精巧，虽然是一个简单的Flip Card 和 计数 Demo

objectivec#import "CardGameViewController.h" @interface CardGameViewController () @property (weak, nonatomic) IBOutlet UILabel *flipsLabel; @property (nonatomic) int flipCount; @end @implementation CardGameViewController - (void) setFlipCount:(int)flipCount {  _flipCount = flipCount;  self.flipsLabel.text = [NSString stringWithFormat:@"Flips: %d",self.flipCount];  NSLog(@"flipCount changed to %d",self.flipCount); } - (IBAction)touchCardButton:(UIButton *)sender {  if ([sender.currentTitle length]) {   [sender setBackgroundImage:[UIImage imageNamed:@"cardback"]         forState:UIControlStateNormal];   [sender setTitle:@"" forState:UIControlStateNormal];  } else {   [sender setBackgroundImage:[UIImage imageNamed: @"cardfront"]         forState:UIControlStateNormal];   [sender setTitle:@"A♣︎" forState:UIControlStateNormal];  }  self.flipCount++; } @end  

很精巧，巧妙在于两处

1. 要制造卡片来回翻装的使用if / else, 利用卡片（实际上是button）两面不同的title长度来翻转卡片
2. 使用私有属性flipCount， 然后将flipsLabel上的数字进行更新

好棒的课程,好大的信息量