Question

我创建了一个NSMutableDictionary以及一个向字典中添加对象的方法。我知道函数addObject正确地将对象添加到字典中，但是稍后当我尝试使用方法Print_Object打印对象时，属于对象的每个变量都打印为null/0。我的代码有问题吗？

-(NSMutableDictionary *)_stock{
    if (!_stock) {
        _stock = [[NSMutableDictionary alloc]init];
    }
    return _stock;  
}

-(void) addObject:(NSString*) desc key: (NSString*) theKey floatrc: (float) retailcost floatwsc: (float) wholesalecost intnoh: (int) numonhand floatns: (int) numsold {
    object_info* obj = [[object_info alloc]init];
    [obj setDescription: desc];
    [obj setRetailCost: retailcost];
    [obj setWholeSaleCost:wholesalecost];
    [obj setNumOnHand: numonhand];
    [obj setNumItemsSold: numsold];
    [self.stock setValue:obj forKey:theKey];   
}

-(void) Print_Object:(NSString *) theKey {
    object_info* obj = [self.stock objectForKey:theKey];
    NSLog(@"Key: %@ Description: %@ Retail Cost: %f Wholesale Cost: %f Number on Hand: %i Number Sold: %i", theKey, obj.description, obj.retail_cost, obj.wholesale_cost, obj.num_on_hand, obj.num_items_sold);     
}

这是object_info的声明：

#import "object_info.h"

@implementation object_info

//Getters
-(NSString *)description {
    return description;
}


-(float) retail_cost {
    return retail_cost;
}

-(float) wholesale_cost {
    return wholesale_cost;
}

-(int) num_on_hand {
    return num_on_hand;
}

-(int) num_items_sold {
    return num_items_sold;
}

//Setters
-(void)setDescription:(NSString *) value {
    description = value;
}

-(void) setRetailCost: (float) n {
    retail_cost = n;
}

-(void) setWholeSaleCost: (float) n {
    wholesale_cost = n;
}

-(void) setNumOnHand: (int) n {
    num_on_hand = n;
}

-(void) setNumItemsSold: (int) n {
    num_items_sold = n;
}

@end

这是object_info.h：

#import <Foundation/Foundation.h>

@interface object_info : NSObject
{
    NSString *description;
    float retail_cost;
    float wholesale_cost;
    int num_on_hand;
    int num_items_sold;
}

-(NSString *)description;
-(void)setDescription:(NSString *)value;

-(float) retail_cost;
-(void) setRetailCost:(float) n;

-(float) wholesale_cost;
-(void) setWholeSaleCost:(float) n;

-(int) num_on_hand;
-(void) setNumOnHand: (int) n;

-(int) num_items_sold;
-(void) setNumItemsSold:(int) n;

@end

Answer 1

您能告诉我们stock的声明吗？我怀疑你已将其声明为@property，在这种情况下，您尝试将-_stock声明为getter将无效。实例变量将为_stock，但getter将仅为-stock。如果这是一个正确的猜测，那么您是NSLog(@"%@", self.stock)您应该看到(null)作为输出 - 您的自定义getter未被调用，因此不会创建任何字典。

您的代码通常看起来很老套;特别是：

你现在几乎从未将实例存储放在@interface内;把它放在@implementation;
您的整个object_info可以重新表述为@property，然后您无需在@implementation内部实现内容，只需允许属性自动合成;
而不是[obj setDescription: desc];等，您现在通常会看到使用点语法，例如obj.description = desc;。编译器仍然会确保调用正确的setter（或getter），它只是一个需要较少心理上下文的表达式，允许直接从左到右读取;
访问字典的更正常的现代方式是dictionary[key] = value存储和dictionary[key]访问。

Answer 2

  [self addObject:@"AAA" key:@"BBB" floatrc:100 floatwsc:200 intnoh:300 floatns:400];
  [self Print_Object:@"BBB"];

这对我来说很好，你用错了钥匙吗？

  [self addObject:@"AAA" key:@"BBB" floatrc:100 floatwsc:200 intnoh:300 floatns:400];
  [self Print_Object:@"AAA"];

这是错误的，因为该对象为零。

  2017-02-16 10:48:34.086 Test[53298:14250944] Key: AAA Description: (null) Retail Cost: 0.000000 Wholesale Cost: 0.000000 Number on Hand: 0 Number Sold: 0

NSMutableDictionary对象无法从方法中正确访问？

2 个答案: