NSDictionary类使用(转)

字典：NSDictionary

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:
Example:

//
 //  MyClass.h
 //  FoundationKit4
 //
 //  Created by Elf Sundae on 10/22/10.
 //  Copyright 2010 Control-Strength. All rights reserved.
 //

#import <Cocoa/Cocoa.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
//  FoundationKit4
//
//  Created by Elf Sundae on 10/22/10.
//  Copyright 2010 Control-Strength. 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

//
 // 示例字典（NSDictionary,NSMutableDictionary）操作
// Elf Sundae  10/22/2010
//

#import <Foundation/Foundation.h>
#import "MyClass.h"

int main (int argc, const char * argv[]) {
    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
   
 // 创建字典：dictionaryWithObjectsAndKeys:
    MyClass *my1 = [MyClass new];
    MyClass *my2 = [MyClass new];
    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(1);
     }
    [sub setFirstName:@"Elf"];
    [sub setLastName:@"Sundae"];
   
    NSLog(@"修改数据： %@",sub);
   
  // 遍历字典
     NSLog(@"***遍历字典myClassDict如下：");
  for (id key in myClassDict)
     {
         NSLog(@"key: %@ ,value: %@",key,[myClassDict objectForKey:key]);
     }
     NSLog(@"***遍历字典myClassDict结束。");
    
  // MARK: ***  添加新元素  ***   
  // NSDictionary无法添加或删除元素，可以使用NSMutableDictionary.
     NSMutableDictionary *myNewDict = [NSMutableDictionary dictionary];
  // 将原有字典添加到新字典的一对元素
  //[myNewDict setObject:myClassDic forKey:@"旧的不可变字典myClassDic"];
    
  // 遍历添加已有数据(原字典)
  for (id key in myClassDict)
     {
         [myNewDict setObject: [myClassDict objectForKey:key]
                   forKey:key];
     }
    
     NSString *newkey = @"newKey";
     NSString *newValue = @"This is a new Value.";
     [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结束。");
    
  // 删除元素
     [myNewDict removeObjectForKey: @"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结束。");
    
     [pool drain];
  return 0;
 }

// 输出结果（省略日期 时间等信息）
修改数据： Elf Sundae
***遍历字典myClassDict如下：
key: my3 ,value: Elf Sundae
key: my4 ,value: No Name found.
key: my1 ,value: No Name found.
key: my2 ,value: No Name found.
***遍历字典myClassDict结束。
***遍历字典myNewDict如下：
key: newKey ,value: This is a new Value.
key: my3 ,value: Elf Sundae
key: my4 ,value: No Name found.
key: my1 ,value: No Name found.
key: my2 ,value: No Name found.
***遍历字典myNewDict结束。
***遍历字典myNewDict如下：
key: my3 ,value: Elf Sundae
key: my4 ,value: No Name found.
key: my1 ,value: No Name found.
key: my2 ,value: No Name found.
***遍历字典myNewDict结束。