CardMatchingGame

• .h

  @import Foundation
  #import "Deck.h"
  @interface CardMatchingGame : NSObject
  - (instancetype)initWithCardCount: (NSUInteger)count usingDeck: (Deck *)deck;
  @property (nonatomic, readonly) NSUInteger score;
  - (void)chooseCardAtIndex: (NSUInteger)index;
  - (Card *)cardAtIndex: (NSUInteger)index;
  @end
  

• .m

  #import "CardMathcingGame.h"
  @interface CardMatchingGame()
  @property (nonatomic, readwrite) NSInteger score;
  @property (nonatomic, strong) NSMutableArray *cards;
  @end
  
  @implementation
  - (NSMutableArray)cards {
        if (!_cards) _cards = [[NSMutableArray alloc] init];
        return _cards;
  }
  
  - (instancetype)initWithCardCount: (NSUInteger)count usingDeck: (Deck *)deck {
        self = [super init];
        if (self) {
            for (int i = 0; i < count; ++i) {
                Card *card = [deck drawRandomCard];
                if (card) {
                [self.cards addObject:card];
              } else {
                    self = nil;
                  break;
              }
          }
      }
        return self;
  }
  
  - (instancetype)init {
        return nil;
  }
  
  - (Card *)cardAtIndex: (NSUInteger)index {
    return (index < [self.cards count]) ? self.cards[index] : nil;
  }
  
  static const int MISMATCH_PENALTY = 2;
  static const int MATCH_BONUS = 2;
  static const int COST_TO_CHOOSE = 1;
  - (void)chooseCardAtIndex: (NSUInteger)index {
    Card *card = [self cardAtIndex: index];
        if (!card.isMatched) {
            if (card.isChosen) {
                card.chosen = NO;
          } else {
                // match against another card
                for (Card *otherCard in self.cards) {
                    if (otherCard.isChosen && !otherCard.isMatched) {
                        int matchScore = [card match:@[otherCard]];
                        if (matchScore) {
                            self.score += matchScore * MATCH_BONUS;;
                            card.matched = YES;
                            otherCard.matched = YES;
                      } else {
                            self.score -= MISMATCH_PENALTY;
                            otherCard.chosen = NO;
                      }
                        break;
                  }
                    
              }
                self.score -= COST_TO_CHOOSE;
                card.Chosen = YES;
          }
      }
  }
  @end
  

其他

• firstObject/lastObject 方法和下标访问的差别在于，这两种方法当越界时会返回 nil，而下标访问会直接崩溃
• 所有的对象一定要记得初！始！化！否则默认是 nil