我们可以为 class object 使用 setvalue 和 forkey 属性吗？

Question

I have a class named "Book" and the source code is as following:-

Book.h

#import <"UIKit/UIKit.h>


@interface Book : NSObject {

    NSInteger bookID;
    NSString *title;    //Same name as the Entity Name.
    NSString *author;   //Same name as the Entity Name.
    NSString *summary;  //Same name as the Entity Name.

}

@property (nonatomic, readwrite) NSInteger bookID;

@property (nonatomic, retain) NSString *title;

@property (nonatomic, retain) NSString *author;

@property (nonatomic, retain) NSString *summary;

@end

Book.m

#import "Book.h"

@implementation Book

@synthesize title, author, summary, bookID;

-(void) dealloc {

    [summary release];
    [author release];
    [title release];
    [super dealloc];
}

@end

Then within another class can I write:-

Book *aBook = [[Book alloc]init];
[aBook setValue:currentElementValue forKey:elementName];

If yes then why?? Because generally setvalue and forkey is used to store data in NSMutableDictionary..

Answer 1

Basically Key-Value coding is intended to work with an object's properties. Key-Value Coding Programming Guide starts with the lines,

Key-value coding is a mechanism for accessing an object's properties indirectly , using strings to identify properties, rather than through invocation of an accessor method or accessing them directly through instance variables. In essence, key-value coding defines the patterns and method signatures that your application's accessor methods implement.

The setObject:forKey: and removeObjectForKey: methods are intended to be used with dictionaries. You can also use setValue:forKey: method to set values to a dictionary. But, you can not use setObject:forKey: method for class objects.

One more difference is that setObject:forKey: doesn't accept nil as the value. Instead you should use NSNull as the value. But setValue:forKey: accepts nil and removes the key from the dictionary, which saves the memory.

[Please someone correct me if I am wrong somewhere!]