在NSMutableArray的for循環中執行實例方法（包含3個對象）

Question

我正在遵循Big Nerd Ranch的Objective-C指南，在其中一項挑戰（第17章）中，他要求您創建3個實例一個你創建的對象，我創建了這個類，實現了setter，getters和兩個實例方法，然後我創建了3個對象實例並定義了所有的變量。然後他會要求你將3個對象放到一個數組中，並用for循環迭代這些值。

我遇到的問題是我不知道如何在「for循環」中執行實例方法。

這是我迄今爲止（所有值是隨機的，假設）：

StockHolding.h

#import <Foundation/Foundation.h> 

@interface StockHolding : NSObject 
{ 
    float purchaseSharePrice; 
    float currentSharePrice; 
    int numberOfShares; 
} 

@property float purchaseSharePrice; 
@property float currentSharePrice; 
@property int numberOfShares; 

- (float)costInDollars; 
- (float)valueInDollars; 

@end 

StockHolding.m

#import "StockHolding.h" 

@implementation StockHolding 

@synthesize purchaseSharePrice, currentSharePrice, numberOfShares; 

- (float)costInDollars; 
{ 
    return purchaseSharePrice * numberOfShares; 
} 
- (float)valueInDollars; 
{ 
    return currentSharePrice * numberOfShares; 
} 

@end 

的main.m

#import <Foundation/Foundation.h> 
#import "StockHolding.h" 


int main(int argc, const char * argv[]) 
{ 

    @autoreleasepool { 

    StockHolding *apple = [[StockHolding alloc] init]; 

     [apple setPurchaseSharePrice: 10]; 
     [apple setCurrentSharePrice: 50]; 
     [apple setNumberOfShares: 20]; 

    StockHolding *hmv = [[StockHolding alloc] init]; 

     [hmv setPurchaseSharePrice: 15]; 
     [hmv setCurrentSharePrice: 0]; 
     [hmv setNumberOfShares: 17]; 

    StockHolding *drpepper = [[StockHolding alloc] init]; 

     [drpepper setPurchaseSharePrice: 5]; 
     [drpepper setCurrentSharePrice: 15]; 
     [drpepper setNumberOfShares: 70]; 


     NSMutableArray *stocksList = [NSArray arrayWithObjects:apple, hmv, drpepper, nil]; 

     for (NSObject z in stocksList) { 

      NSLog(@"Original cost: %@", [z costInDollars]); 
      NSLog(@"Current value: %@", [z valueInDollars]); 

     } 

    } 
    return 0; 
} 

Answer 1

你的家庭工作很好。

沒有編譯就很難發現錯誤。

• 在NSLog您使用％@爲[stockObj costInDollars]返回float，所以這裏是一個錯誤。使用%f

你只需要在你的代碼的一些潤色。

1. 良好的命名約定。

2. 的使用for(StockHolding *stockObj in stocksList)到位for (NSObject z in stocksList)

   for (StockHolding *stockObj in stocksList) { 
       NSLog(@"Original cost: %f", [stockObj costInDollars]);//%f as costInDollars returns float not an object 
       NSLog(@"Current value: %f", [stockObj valueInDollars]);//same as above 
   } 
   

3. 的ivars可以跳過，@property將工作良好。

4. @synthesize在新編譯器中不需要。如果您使用，請嘗試每行使用一個屬性。

5. 相反的分配值：

   StockHolding *apple = [[StockHolding alloc] init]; 
   [apple setPurchaseSharePrice: 10]; 
   [apple setCurrentSharePrice: 50]; 
   [apple setNumberOfShares: 20]; 
   

   您可以使用：

   StockHolding *apple=[[StockHolding alloc]initWithPurchaseSharePrice:10 currentSharePrice:50 numberOfShares:20]; 
   

   爲此，您需要創建一個方法：

   -(StockHolding *)initWithPurchaseSharePrice:(float)purchase currentSharePrice:(float)current numberOfShares(int):numbers]; 
   

6. 而不是NSMutableArray *stocksList = [NSArray arrayWithObjects:apple, hmv, drpepper, nil];你可以使用：

   NSMutableArray *stocksList=@[apple, hmv, drpepper]; 
   

編輯：

要打印stockObject：呼叫以下方法[self printStockObject:stockObject];

-(void)printStockObject:(StockHolding *)stockObj{ 
    NSLog(@"Purchase Price : %f",stockObj.purchaseSharePrice); 
    NSLog(@"Current Price : %f",stockObj.currentSharePrice); 
    NSLog(@"Number of Shares : %d",stockObj.numberOfShares); 
} 

Answer 2

你也會知道我可以打印stockObj中的NSLog的名字嗎？我試過NSLog（@「％@」，stockObj）;但它只是返回內存地址。

覆蓋-description

-(NSString *)description { 
    return [NSString stringWithFormat:@"%@: purchase price: %f current price: %f, number of shares: %d", NSStringFromClass([self class]), self.purchaseSharePrice, self. currentSharePrice, self.numberOfShares]; 
} 

如果你也想在超類的description，做

[NSString stringWithFormat:@"%@: purchase price: %f current price: %f, number of shares: %d %@", NSStringFromClass([self class]), self.purchaseSharePrice, self. currentSharePrice, self.numberOfShares, [super description]]; 

---

AKV寫道，你應該循環是這樣的：

for (StockHolding *stockObj in stocksList) { 
    NSLog(@"%@",stockObj); 
} 

這是正確的。但是，如果你有其他的對象比在列表StockHolding，你也可以做

for (id stockObj in stocksList) { 
    NSLog(@"%@",stockObj); 
} 

，你可以發送任何消息id - 如果實現了，它會工作，否則崩潰。注意NSObject和id是不一樣的。

---

在現代版本的Xcode中，你不需要聲明iVars。你不需要綜合。

@interface StockHolding : NSObject 

@property float purchaseSharePrice; 
@property float currentSharePrice; 
@property int numberOfShares; 
@property (copy) NSString *shareName; 


- (float)costInDollars; 
- (float)valueInDollars; 

@end 

如果你不合成，實例變量名稱將是屬性的名稱與_ -prefix

shareName - >_shareName

StockHolding *apple = [[StockHolding alloc] init]; 
[apple setPurchaseSharePrice: 10]; 
[apple setCurrentSharePrice: 50]; 
[apple setNumberOfShares: 20]; 
[apple setShareName:@"apple"]; 

-description可能看起來像

-(NSString *)description { 
    return [NSString stringWithFormat:@"%@: %@ purchase price: %f current price: %f, number of shares: %d", NSStringFromClass([self class]),_shareName, self.purchaseSharePrice, self. currentSharePrice, self.numberOfShares]; 
}