NSMutableDictionary

NSMutableDictionary 用于处理值对集合。保存到键的对象必须实现了copyWithZone:方法。和NSMutableArray一样添加到容器时对象收到retain消息，把对象从容器中移除时收到release消息，任何想在移除对象还要对该对象进行操作必须先对该对象发出一条retain消息，在使用完成后需要release。

#import <Foundation/Foundation.h>

int main (int argc, const char * argv[])
{

    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

    //创建Dictionary,Capacity仅控制初始化大小
    NSMutableDictionary *fruits = [NSMutableDictionary dictionaryWithCapacity:2];
    [fruits setObject:@"Orange" forKey:@"OrangeKey"];
    [fruits setObject:@"Apple" forKey:@"AppleKey"];
    [fruits setObject:@"Blueberry" forKey:@"BlueberryKey"];
    NSLog(@"%@", fruits);
    
    //获取一个对象
    id oneObj = [fruits objectForKey:@"AppleKey"];
    NSLog(@"%@", oneObj);

    //如果找不到应的条目，返加nil
    id noObj = [fruits objectForKey:@"aaa"];
    NSLog(@"%@", noObj);
    
    [pool drain];
    return 0;
}