如何在其他方法中访问字典？

Question

下面是我用来尝试通过另一种方法访问初始化字典的代码：

#import "UserFoodData.h"

@implementation UserFoodData

-(void)loadUserFoodData{
    NSString *appDataPath = [[NSBundle mainBundle] pathForResource:@"UserFoodData"     ofType:@"plist"];
    NSMutableDictionary *userFoodDictionary = [[NSMutableDictionary alloc]     initWithContentsOfFile:appDataPath];

    for (userFoodDictionary in userFoodDictionary){
        NSLog(@"%@", userFoodDictionary);
    }

}

-(void)setName:(NSString *)foodName andCarbs:(NSNumber *)carbAmount{
    [userFoodDictionary setObject:foodName forKey:foodName];

}

@end

我似乎收到的错误消息是：使用未声明的标识符'userFoodDictionary'

现在我认为是错误的，因为编译器认为setName：andCarbs方法有可能只能在初始化应用程序主屏幕时调用的loadUserFoodData之前执行。 有人可以帮我解决问题吗？

Answer 1

我似乎收到的错误消息是：

使用未声明的标识符“ userFoodDictionary”

编译器说：

1.我没有在本地看到任何变量，例如userFoodDictionary或-（void）setName：（NSString *）foodName和Carbs：（NSNumber *）carbAmount中的实例变量。

2.但是您正在尝试访问它。

 and also your for loop has mistakes. please verify my answer

编译器正在尝试在“ UserFoodData”类中查找userFoodDictionary。 因为您要在loadUserFoodData方法之外访问userFoodDictionary。 因此，为了访问本地方法之外的内容，必须将该引用保留在头文件中，然后可以在类中的任何位置访问它。

@interface UserFoodData : NSObject

@property(nonatomic,retain)NSMutableDictionary *userFoodDictionary;

@end

#import "UserFoodData.h"

@implementation UserFoodData
//@synthesize userFoodDictionary; synthesise is automatically entered by compiler

-(void)loadUserFoodData{
    NSString *appDataPath = [[NSBundle mainBundle] pathForResource:@"UserFoodData"     ofType:@"plist"];

    self.userFoodDictionary = [[NSMutableDictionary alloc]     initWithContentsOfFile:appDataPath];

//Please not down this
    for (id aFood in userFoodDictionary){
        NSLog(@"%@", aFood);
    }

}

-(void)setName:(NSString *)foodName andCarbs:(NSNumber *)carbAmount{
    [self.userFoodDictionary setObject:foodName forKey:foodName];

}

@end

Answer 2

我假设您在发布的第二种方法中遇到了错误。

- (void)setName:(NSString *)foodName andCarbs:(NSNumber *)carbAmount{
    [userFoodDictionary setObject:foodName forKey:foodName];
}

该方法未定义userFoodDicitionary 。 如果您希望字典在方法调用之间持久存在，请将其存储在@property 。

您应该真正阅读了Objective-C的入门资料，您可以从这份Apple文档开始

Answer 3

这里有多个问题...

一方面，您的for循环有一个语法错误……不仅如此，而且您正尝试通过一个名为userFoodDictionary的字典进行迭代， userFoodDictionary使用一个迭代器变量也称为userFoodDictionary 。 更改为类似：

for (id dictKey in userFoodDictionary) {
    NSLog(@"%@", dictKey);
}

您还试图访问超出范围的变量。 userFoodDictionary在loadUserFoodData的范围内声明。 该方法完成后，将释放该变量，因此您当然不能在setName:andCarbs:访问它。 为此，您需要在更广泛的范围内进行定义-创建属性，静态变量，iVar等。

这里缺少许多OOP概念...如果您是编程的新手，那么Objective-C是一个很难入门的地方，它可能会使您陷入很多循环（双关语）。

Answer 4

尝试这个...

#import "UserFoodData.h"

@implementation UserFoodData

-(void)loadUserFoodData{
    NSString *appDataPath = [[NSBundle mainBundle] pathForResource:@"UserFoodData"     ofType:@"plist"];
    NSMutableDictionary *userFoodDictionary = [[NSMutableDictionary alloc]     initWithContentsOfFile:appDataPath];

    for (userFoodDictionary in userFoodDictionary){
        NSLog(@"%@", userFoodDictionary);
    }

}

-(void)setName:(NSString *)foodName andCarbs:(NSNumber *)carbAmount{
    NSString *appDataPath = [[NSBundle mainBundle] pathForResource:@"UserFoodData"     ofType:@"plist"];
    NSMutableDictionary *userFoodDictionary = [[NSMutableDictionary alloc]     initWithContentsOfFile:appDataPath];
    [userFoodDictionary setObject:foodName forKey:foodName];
}

@结束

让我知道是否有帮助... :)

Answer 5

我认为问题是您的NSMutableDictionary应该是在.h中声明为NSMutableDictionary的ivar，如下所示

NSMutableDictionary *userFoodDictionary

在.m中

-(void)loadUserFoodData{
    NSString *appDataPath = [[NSBundle mainBundle] pathForResource:@"UserFoodData"     ofType:@"plist"];
    userFoodDictionary = [[NSMutableDictionary alloc]     initWithContentsOfFile:appDataPath];

for (userFoodDictionary in userFoodDictionary){
    NSLog(@"%@", userFoodDictionary);
}

}
-(void)setName:(NSString *)foodName andCarbs:(NSNumber *)carbAmount{
    [userFoodDictionary setObject:foodName forKey:foodName];

}

Answer 6

所以问题在下面的行中

for (userFoodDictionary in userFoodDictionary){
    NSLog(@"%@", userFoodDictionary);
}

替换为

for (NSMutableDictionary *userFoodDic in userFoodDictionary){
    NSLog(@"%@", userFoodDic);
}

可以解决您的问题

好，也有其他问题

请也将userFoodDictionary声明为属性之一，如@Sebastian在其回答中所述：)