Question

我在上课时遇到了麻烦。我必须创建“StockHolding”对象，它们是NSObject的子类。我创建实例变量和方法。然后我创建了3个完整的股票代码和名称和价格，并将它们加载到一个可变数组中。我很难快速枚举数组中的对象并打印每个对象的属性（价格）。问题是我在尝试枚举对象并打印属性时遇到错误。我尝试过几种不同的方法来解决这个问题而没有运气。有任何想法吗？我还注意到currentStock没有打印名称，而是指针位置。也许这些问题是相关的。提前谢谢。

'标题'

#import <Foundation/Foundation.h>

@interface StockHolding : NSObject
{
    float fPurchaseSharePrice; 
    float fCurrentSharePrice; 
    int iNumberOfShares;
}

@property float fPurchaseSharePrice;
@property float fCurrentSharePrice;
@property int iNumberOfShares;

-(float) fCostInDollars; //fPurchaseSharePrice * fNumberOfShares
-(float) fValueInDollars; //fCurrentSharePrice * fNumberOfShares

@end

'执行'

#import "StockHolding.h"

@implementation StockHolding

@synthesize fCurrentSharePrice, fPurchaseSharePrice, iNumberOfShares;

-(float)fCostInDollars; //fPurchaseSharePrice * iNumberOfShares
{    
    return (fPurchaseSharePrice * iNumberOfShares);
}

-(float)fValueInDollars; //fCurrentSharePrice * iNumberOfShares
{
    return (fCurrentSharePrice * iNumberOfShares);
}

@end

'主'

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

@autoreleasepool {
    StockHolding *Apple = [[StockHolding alloc] init];
    [Apple setFPurchaseSharePrice:225];
    [Apple setFCurrentSharePrice:300];
    [Apple setINumberOfShares:50];

    StockHolding *Cisco = [[StockHolding alloc] init];
    [Cisco setFPurchaseSharePrice:100];
    [Cisco setFCurrentSharePrice:50];
    [Cisco setINumberOfShares:75];

    StockHolding *WalMart = [[StockHolding alloc] init];
    [WalMart setFPurchaseSharePrice:75];
    [WalMart setFCurrentSharePrice:150];
    [WalMart setINumberOfShares:75];

    NSMutableArray *Portfolio = [NSArray arrayWithObjects: Apple, Cisco, WalMart, nil];

    for (NSObject *currentStock in Portfolio){   
        NSLog(@"Purchase Price: %@", currentStock );
        NSLog(@"Details: %f", [currentStock FPurchaseSharePrice]);  //  <---Error is on this line.  It says "No visible @interface for NSObject declares the selector fPurchaseSharePrice"
    }

}
return 0;
}

Answer 1

而是为你的for循环执行此操作

for (StockHolding *currentStock in Portfolio){   
    NSLog(@"Purchase Price: %@", currentStock );
    NSLog(@"Details: %f", [currentStock fPurchaseSharePrice]);  //  <---Error is on this line.  It says "No visible @interface for NSObject declares the selector fPurchaseSharePrice"
}

Answer 2

在您的NSLog中：FPurchaseSharePrice应为fPurchaseSharePrice。

此外，如果覆盖 - （NSString *）描述，打印对象将产生该字符串，而不是您当前看到的该对象的指针。

- (NSString *)description
{
    return [NSString stringWithFormat:@"StockHolding: %.2f, %.2f", self.fCostInDollars, self.fValueInDollars];
}

收率：

Purchase Price: StockHolding: 11250.00, 15000.00

而不是：

Purchase Price: <StockHolding: 0x7fe438c0a480>

最后，您可以执行以下操作：

，而不是在for循环中转换为NSObject

for (StockHolding *currentStock in Portfolio)

可能没有回应的错误会消失。

Answer 3

好吧，就像它说：你没有一个有这个名字的方法。在Objective-C中，方法名称区分大小写，并且您将属性（和相应的访问者）声明为fPurchaseSharePrice。你想用这个：

NSLog(@"Details: %f", [currentStock fPurchaseSharePrice]);

Big Nerd Ranch Objective C第17章挑战 - 定义类

3 个答案: