Question

我一直在使用Big Nerd Ranch的Objective-C指南，但我在显示我创建的课程中的所有项目时遇到了问题。有关更多参考，第17章中有关股票的挑战。我知道这个问题还有其他问题，但是我已经检查了所有其他问题的纠正代码，问题仍然存在。出于某种原因，只显示Facebook费用。这是我的工作：的 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;
@synthesize currentSharePrice;
@synthesize numberOfShares;


-(float)costInDollars
{

    return numberOfShares*purchaseSharePrice;
}


-(float)valueInDollars
{

    return numberOfShares*currentSharePrice;
}


@end

的main.m

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

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

    @autoreleasepool {

        StockHolding *apple, *google, *facebook = [[StockHolding alloc] init];

        [apple setNumberOfShares:43];
        [apple setCurrentSharePrice:738.96];
        [apple setPurchaseSharePrice:80.02];

        [google setNumberOfShares:12];
        [google setCurrentSharePrice:561.07];
        [google setPurchaseSharePrice:600.01];

        [facebook setNumberOfShares:5];
        [facebook setCurrentSharePrice:29.33];
        [facebook setPurchaseSharePrice:41.21];


         NSLog(@"%.2f.", [apple costInDollars]);
         NSLog(@"%.2f.", [google costInDollars]);
         NSLog(@"%.2f.", [facebook costInDollars]);



    }
    return 0;
}

感谢您的帮助！

Answer 1

StockHolding *apple, *google, *facebook = [[StockHolding alloc] init];

此行仅分配了最后一个facebook变量，因此当您向其添加项目时，apple和google仍为nil。

现在，由于Obj-C动态地将消息分派给对象，因此当您尝试使用nil向[google setNumberOfShares:12]变量添加项目或调用[apple costInDollars]时，不会引发错误。

尝试：

StockHolding *apple = [[StockHolding alloc] init], *google = [[StockHolding alloc] init], *facebook = [[StockHolding alloc] init];

我班上只展示了几件物品？

1 个答案: