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：objectForKeyNSMutableDictionary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@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#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(1); } [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 0;}