iphone - NSDictionary 可能无法响应 setObject :forKey on a NSMutableDictionary object

Question

我是 Xcode 新手，正在尝试这个小程序。

//  BookStoreMine.h
//  BookStore

#import <Cocoa/Cocoa.h>
#import "Book.h"

@interface BookStoreMine : NSObject {
NSDictionary* mybookStore;

}
@property (retain) NSDictionary* myBookStore;

-(id)init;
-(void)printInventory;
-(BOOL)addBook:(Book *)newBook;
-(BOOL)removeBookWithTitle:(NSString *)whichTitle;
-(void)dealloc;

@end

//  BookStoreMine.m
//  BookStore
#import "BookStoreMine.h"


@implementation BookStoreMine
@synthesize myBookStore;

-(id)init {
    self = [super init];
    if (self != nil) {
    myBookStore = [[NSMutableDictionary alloc] init];
}
return self;
}

-(BOOL)addBook:(Book *)newBook {
**[myBookStore setObject:newBook forKey:newBook.title];**
return YES;
}    

-(BOOL) removeBookWithTitle:(NSString *)whichTitle{
if ([myBookStore objectForKey:whichTitle] != nil) {
    **[myBookStore removeObjectForKey:whichTitle];**
    return YES;
}
return NO;
}

-(void)printInventory{
Book *book;
for (NSString* key in myBookStore) {
    book = [myBookStore objectForKey:key];
    NSLog(@" Title: %@",book.title);
    NSLog(@" Author: %@",book.author);
    NSLog(@" Description: %@",book.description);
    NSLog(@"ID is:%@",book.ID);
}
}

-(void)dealloc{
self.myBookStore = nil;
[super dealloc];
}

@end

当我在 myBookStore 上使用 setObject 方法以及在 myBookStore 对象上使用 removeObject 方法时，我会收到警告。警告是“NSDictionary 可能不会响应 setObject:forKey 或 removeObject:forKey。当我使用的对象是 NSMutableDictionary 时，为什么会收到与 NSDictionary 相关的警告？如何摆脱警告？(PS:程序编译运行没有任何问题)

Answer 1

在运行时，您将myBookStore对象设置为NSMutableDictionary的实例。

在编译时，它仍然被声明为NSDictionary，它不会响应设置或删除的消息。

如果将变量声明为 NSMutableDictionary，警告将会消失。