日期转换

- (void)viewDidLoad {
    [super viewDidLoad];

    NSDate *currentDate = [NSDate date];
    //传入一个日期  判断这个日期是今天 明天 还是昨天
    [self compareDate:currentDate];
    
    //传入今天的时间，返回今天后14天的时间
    for (int i=1; i<15; i++) {
        NSLog(@"========%@日",[self GetTomorrowDay:currentDate index:i]);
    }

    NSLog(@"获取当地时间===%@",[self getCurrentTime]);
}

//获取当地时间
- (NSString *)getCurrentTime {
    NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
    [formatter setDateFormat:@"yyyy-MM-dd"];
    NSString *dateTime = [formatter stringFromDate:[NSDate date]];
    return dateTime;
}
//将字符串转成NSDate类型
- (NSDate *)dateFromString:(NSString *)dateString {
    
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setDateFormat: @"yyyy-MM-dd"];
    NSDate *destDate= [dateFormatter dateFromString:dateString];
    return destDate;
}


//传入今天的时间，返回今天后多少天的时间    (返回明天的时间  index=1)
- (NSString *)GetTomorrowDay:(NSDate *)aDate index:(NSInteger)index{
    NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSCalendarIdentifierGregorian];
    NSDateComponents *components = [gregorian components:NSCalendarUnitWeekday | NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay fromDate:aDate];
    [components setDay:([components day]+index)];
    NSDate *beginningOfWeek = [gregorian dateFromComponents:components];
    NSDateFormatter *dateday = [[NSDateFormatter alloc] init];
    [dateday setDateFormat:@"MM-dd"];
    return [dateday stringFromDate:beginningOfWeek];
}

// 传入一个日期  判断这个日期是今天 明天 还是昨天
-(NSString *)compareDate:(NSDate *)data{

    NSTimeInterval secondsPerDay=24*60*60;
    NSDate *today=[[NSDate alloc]init];
    NSDate *tomorrow,*yesterday;
    tomorrow=[today dateByAddingTimeInterval:secondsPerDay];
    yesterday=[today dateByAddingTimeInterval:-secondsPerDay];
    
    NSString *todayString=[[today description]substringToIndex:10];
    NSString *yesterdayString=[[today description]substringToIndex:10];
    NSString *tomrrowString=[[today description]substringToIndex:10];
    
    NSString *dateString =[[data description]substringToIndex:10];
    
    if ([dateString isEqualToString:todayString]) {
        return @"今天";
    }else if ([dateString isEqualToString:yesterdayString]){
         return @"昨天";
    }else if ([dateString isEqualToString:tomrrowString]){
         return @"明天";
    }else{
        NSLog(@"%@",dateString);
        return dateString;
    }
}