类的扩展(Extension , NSData, NSDateFormatter, Category, Extension, Protocol, delegate)

        NSDate *date = [NSDate date];
        NSLog(@"%@", date);

        //NSTimeInterval = double
        NSDate *date1 = [NSDate dateWithTimeIntervalSinceNow:60];
        NSLog(@"%@", date1);
        
        //昨天的现在时刻
        NSDate *yesterday = [NSDate dateWithTimeIntervalSinceNow:(-1 * (24 * 60 * 60))];
        NSLog(@"%@", yesterday);
        
        //明年的现在时刻
        NSDate *nextYear = [NSDate dateWithTimeIntervalSinceNow:366 * 24 * 60 * 60];
        NSLog(@"%@", nextYear);
        
        //昨天的现在时刻 与 明年的现在时刻 间隔多少秒
        NSTimeInterval interval = [yesterday timeIntervalSinceDate:nextYear];
        NSLog(@"%lf", interval);

        //创建一个时间戳
        //把日期转化成时间戳
        NSTimeInterval timestamp = [date timeIntervalSince1970];
        NSLog(@"%lf", timestamp);
        
        //把时间戳转化成日期
        NSTimeInterval timestamp1 = 200;
        NSDate *date2 = [NSDate dateWithTimeIntervalSince1970:timestamp1];
        NSLog(@"%@", date2);

NSTimeZone *timeZone = [NSTimeZone timeZoneWithAbbreviation:@"GMT"];
        [formatter setTimeZone:timeZone];

        NSString *dateString = [formatter stringFromDate:date];
        NSLog(@"%@", dateString);

        NSString *string = @"2014年05月01日 10点23分18秒";
        [formatter setDateFormat:@"yyyy年MM月dd日 HH点mm分ss秒"];
        [formatter setTimeZone:[NSTimeZone timeZoneWithAbbreviation:@"GMT"]];
        NSDate *stringDate = [formatter dateFromString:string];
        NSLog(@"%@", stringDate);

1.
Person_Cosplay.h
#import "Person.h"

@interface Person ()

- (void)dance;

@end

2.
Person.m
@interface Person () {
    NSInteger _age;
}

- (void)dance;

@end

@implementation Person

- (void)setName:(NSString *)name {
    _name = name;
}
- (NSString *)name {
    return _name;
}

- (void)eat {
    NSLog(@"吃个便饭");
    [self dance];
}

- (void)dance {
    NSLog(@"动次打次");
}
@end

NSString+play.h
#import <Foundation/Foundation.h>
@interface NSString (play)
/*
{
    CGFloat _price;
}
*/
- (void)playBasketball;
@end

NSString+play.m
#import "NSString+play.h"
@implementation NSString (play)
- (void)playBasketball {
    NSLog(@"怒扣敬明");
}
@end

    main.m
        NSString *string2 = [[NSString alloc] init];
        [string2 playBasketball];

Love.h//协议
#import <Foundation/Foundation.h>
@protocol Love <NSObject>
@required//必须遵守的(默认值)
- (void)buyFood;
- (void)sendWater;
@optional//可选的
- (void)buyiPhone;
@end

Student.h
#import <Foundation/Foundation.h>
//一个类如何遵守协议
//1.引入协议
#import "Love.h"
//2.遵守协议
@interface Student : NSObject <Love>
@end

Student.m
#import "Student.h"
@implementation Student
- (void)buyFood {
    NSLog(@"早起, 排队, 买热包子, 小跑送到楼下");
}
- (void)sendWater {
    NSLog(@"大热天, 排队接水, 送到楼下");
}
- (void)buyiPhone {
    NSLog(@"省吃俭用, 中午不吃饭, 晚上辣椒蘸酱油, 坚持了一年, 终于攒够了公交费到那里, 卖了个肾, 买了个iPhone送给TA, Ta说分手吧");
}
@end

main.m
        Student *stu = [[Student alloc] init];
        [stu buyFood];
        [stu sendWater];
        [stu buyiPhone];

Woman.h
#import <Foundation/Foundation.h>
#import "Nurse.h"
@interface Woman : NSObject {
    //delegate实例变量
    //1.因为不确定最终找到的保姆是什么类型, 类型用id
    //2.并不是所有人都可以当保姆, 必须遵守协议
    //注: id<Nurse>, 基于类型的限定 
    id<Nurse> _delegate;
}
- (void)setDelegate:(id<Nurse>)delegate;
- (id<Nurse>)delegate;
- (void)work;
- (void)cook;
- (void)takeCareOfBaby;
@end

Woman.m
#import "Woman.h"
@implementation Woman
- (void)setDelegate:(id<Nurse>)delegate {
    _delegate = delegate;
}
- (id<Nurse>)delegate {
    return _delegate;
}
- (void)work {
    NSLog(@"辛苦工作");
}
- (void)cook {
//     NSLog(@"精心做饭");
    //判断代理有没有做饭的能力(判断delegate是否相应canCook这个方法)
    if ([_delegate respondsToSelector:@selector(canCook)]) {
         [_delegate canCook];
    }
   
}
- (void)takeCareOfBaby {
//     NSLog(@"耐心照看孩子");
    if ([_delegate respondsToSelector:@selector(canTakeCareOfBaby)]) {
        [_delegate canTakeCareOfBaby];
    }
    
}
@end

Nurse.h//协议
#import <Foundation/Foundation.h>
@protocol Nurse <NSObject>
- (void)canCook;
- (void)canTakeCareOfBaby;
@end

Chef.h
#import <Foundation/Foundation.h>
#import "Nurse.h"
@interface Chef : NSObject<Nurse>
@end

Chef.m
#import "Chef.h"
@implementation Chef
- (void)canCook {
    NSLog(@"做了蚂蚁上树, 锅包肉, 小鸡炖蘑菇, 铁锅炖大鹅");
}
- (void)canTakeCareOfBaby {
    NSLog(@"厨师教孩子刀法");
}
@end

main.m
Woman *woman = [[Woman alloc] init];
        [woman work];
        [woman cook];
        [woman takeCareOfBaby];        
        Chef *chef = [[Chef alloc] init];      
        //妇女设定代理是厨师
        [woman setDelegate:chef];    
        //妇女想要做饭
        [woman cook];
        [woman takeCareOfBaby];