Objective-C ::使用方法更改對象

Question

我有一個名爲「CardSet」的類，其中包含一個用於容納「卡片」的NSMutableArray * cardSet，我將其擴展爲製作「DeckCards」。我想要「CardSet」有一個名爲「（void）addCard：（Card *）」（以及類似的方法「removeCard」）的方法。我想要「addCard」，以便如何訪問並設置cardSet。更好的是，我想使用「addCard」方法初始化cardSet。類文件 「CardSet.h」 記載：

#import <Cocoa/Cocoa.h> 

#import <Card.h> 

@interface CardSet : NSObject { 

    NSMutableArray* cardSet; 

} 

-(id)init; 

-(NSMutableArray*)getCardSet; 

-(void)setCardSet:(NSMutableArray *)new_cardset; 

-(Card*)getCard:(NSInteger) index; 

**-(void)addCard:(Card*) new_card;** 

-(void)removeCard:(Card*) old_card; 

-(void)dealloc; 

@property (readwrite, retain, getter=getCardSet, setter=setCardSet) NSMutableArray* cardSet; 

@end 

和方法文件讀取：

#import "CardSet.h" 

@implementation CardSet 

-(id)init{ 
    if(self = [super init]){} //will add initialisations here later 
    return self; 
} 

-(NSMutableArray*)getCardSet{ 
    return cardSet; 
} 

-(void)setCardSet:(NSMutableArray *)new_cardSet{ 
    cardSet = new_cardSet; 
} 

-(Card*)getCard:(NSInteger)index{ 
    return [cardSet objectAtIndex:index]; 
} 

**-(void)addCard:(Card *)new_card{ 
    [cardSet addObject:new_card]; 
}** 

-(void)removeCard:(Card *)old_card{ 
    [cardSet removeObject:old_card]; 
} 

-(void)dealloc{ 
    [cardSet release]; 
    [super dealloc]; 
} 

@synthesize cardSet; 

@end 

這編譯就好了。我想用它的「addCard」方法初始化一個「DeckCards」實例52次。當我在DeckCards setter方法中調用addCard 52次並詢問其「cardSet」的大小時，我返回0.

這似乎是一個範圍或特權問題？ 「addCard」方法是否具有setter特權？必須使用setter參數與返回和相應的成員類型相同？

[我可以通過在「DeckCard」之外創建一個NSMutableArray對象「deck_cards_temp」來解決上述問題，向其中添加52張卡片，並通過setter繼承「DeckCards」 CardSet」。這是不是很滿意！]

你有什麼建議？非常感謝您的幫助和耐心。

Answer 1

你永遠不會實際創建cardSet對象。你應該在你-init方法來創建它：

-(id)init 
{ 
    if(self = [super init]) 
    { 
     cardSet = [[NSMutableArray alloc] init]; 
    } 
    return self; 
} 

因爲你從來沒有真正創建磁盤陣列，所有-addCard:的呼叫被髮送給nil對象。

當您將一個數組傳遞給-setCardSet:時，您傳遞的是初始化數組，因此該數組不再爲零，並且-addCard:調用正常工作。

Answer 2

CardSet.h

#import <Cocoa/Cocoa.h> 

// For know we just need to know there is a class named "Card" being used but implemented later 
@class Card; 

@interface CardSet : NSObject { 
    NSMutableArray *cardSet; 
} 

// Here are the methods according to "correct" naming conventions 
- (Card *)cardAtIndex:(NSInteger)index; 
- (void)addCard:(Card *)card; 
- (void)removeCard:(Card *)card; 

// This will help us and forget about writing the setter/getter 
@property (nonatomic, retain) NSMutableArray *cardSet; 

@end 

CardSet.m

#import "CardSet.h" 
// Now we tell the compiler what "Card" is and what methods etc. it has 
#import "Card.h" 

@implementation CardSet 

@synthesize cardSet; 

- (id)init { 
    if (self = [super init]) { 
     // If we don't create the cardSet, how are we able to work with it!? 
     NSMutableArray *anArray = [[NSMutableArray alloc] init]; 
     self.cardSet = anArray; 
     [anArray release]; 
    } 
    return self; 
} 

- (Card *)cardAtIndex:(NSInteger)index { 
    return [cardSet objectAtIndex:index]; 
} 

- (void)addCard:(Card *)card { 
    [cardSet addObject:card]; 
} 

- (void)removeCard:(Card *)card { 
    [cardSet removeObject:card]; 
} 

- (void)dealloc { 
    [cardSet release]; 
    [super dealloc]; 
} 

@end 

正如Abizern已經指出：命名的數組一樣類是一件壞事。

Answer 3

我會縮短該init方法：

- (id)init { 
    if (self = [super init]) { 
     // If we don't create the cardSet, how are we able to work with it!? 
     self.cardSet = [NSMutableArray array]; 
    } 
    return self; 
}