字典：NSDictionary的应用举例

字典就是关键字及其定义（描述）的集合。Cocoa中的实现字典的集合NSDictionary在给定的关键字（通常是一个NSString）下存储一个数值（可以是任何类型的对象）。然后你就可以用这个关键字来查找相应的数值。
不同于数组，字典（也被称为散列表或关联数组）使用的是键查询的优化存储方式。它可以立即找出要查询的数据，而不需要遍历整个数组进行查找。
可使用dictionaryWithObjectsAndKeys来创建字典
查询字典的值：objectForKey
NSMutableDictionary的dictionary方法可以创建一个可变字典，也可以使用dictionaryWithCapaticy：。
使用 setObject:forkey: 方法添加字典元素，如果关键字已存在，则用新植替换旧值。
类似的，NSMutableDictionary类允许随意添加或删除字典元素。
添加元素：setObject:forkey:
删除元素：removeObjectForKey:

#import <Foundation/Foundation.h>
 
@interface MyClass : NSObject
{
    NSString *firstName;
    NSString *lastName;
}
-(void) setFirstName:(NSString*)m_firstName;
-(NSString*)firstName;
 
-(void) setLastName:(NSString*)m_lastName;
-(NSString*)lastName;
@end

//
//  MyClass.m
//  Dictionary
//
//  Created by Aron-Mac-VM on 3/14/16.
//  Copyright (c) 2016 PQLabs. All rights reserved.
//
 
#import "MyClass.h"
 
@implementation MyClass
-(void)setFirstName:(NSString *)m_firstName
{
    firstName = m_firstName;
}
-(NSString*)firstName
{
    return firstName;
}
 
-(void)setLastName:(NSString *)m_lastName
{
    lastName = m_lastName;
}
-(NSString*)lastName
{
    return lastName;
}
 
-(NSString*)description
{
    if(firstName == nil || lastName == nil)
    {
        return @"No Name found.";
    }
    else
    {
        return [NSString stringWithFormat:@"%@ %@",firstName,lastName];
    }
}
@end

//
//  main.m
//  Dictionary
//
//  Created by Aron-Mac-VM on 3/14/16.
//  Copyright (c) 2016 PQLabs. All rights reserved.
//
 
#import <Foundation/Foundation.h>
#import "MyClass.h"
int main(int argc, const char * argv[])
{
 
    @autoreleasepool {
 
        MyClass *my1 = [MyClass new];
        MyClass *my2 = [[MyClass alloc]init];
        MyClass *my3 = [MyClass new];
        MyClass *my4 = [MyClass new];
 
        NSDictionary *myClassDict;
        myClassDict = [NSDictionary dictionaryWithObjectsAndKeys:my1, @"my1",
            my2, @"my2",
            my3, @"my3",
            my4, @"my4",nil];
 
        //获取值objectForkey
        MyClass *sub = [myClassDict objectForKey:@"my3"];
        if(sub==nil)
        {
            exit();
        }
        [sub setFirstName:@"pan"];
        [sub setLastName:@"Sunde"];
        NSLog(@"mofiy the data: %@",sub);
 
        //遍历字典
        for(id key in myClassDict)
        {
            NSLog(@"key: %@, value: %@",key,[myClassDict objectForKey:key]);
        }
        //添加新元素
        //NSDictionary无法添加或者删除元素，可以使用NSMutableDictionary
 
        NSMutableDictionary *myNewDict = [NSMutableDictionary dictionary];
 
        //把原有的字典添加到新字典的一对元素
        [myNewDict setObject:myClassDict forKey:@"旧的不可变字典myClassDict"];
 
        //遍历添加已有数据(原字典)
        for(id key in myClassDict)
        {
            [myNewDict setObject:[myClassDict objectForKey:key] forKey:key];
        }
        NSString *newValue = @"This is a new Value";
        NSString *newKey = @"a new Key";
        [myNewDict setObject:newValue forKey:newKey];
 
        //遍历myNewDict
        NSLog(@"*********遍历字典myNewDict如下:");
        for(id key in myNewDict)
        {
            NSLog(@"Key: %@, value: %@",key,[myNewDict objectForKey:key]);
 
        }
        NSLog(@"*********遍历字典myNewDict Over:");
        //删除元素
 
        [myNewDict removeObjectForKey:@"a new Key"];
        for(id key in myNewDict )
        {
            NSLog(@"key: %@,value: %@",key,[myNewDict objectForKey:key]);
 
        }
 
    }
 
    return ;
}