NSCalendar和NSDateComponents使用

用NSDate可以获取当前日期，但是主要是用以毫秒数体现，用来表示UTC时间很方便。但是如果希望得到用int类型表示的年月日等信息，还需要用到NSCalendar和NSDateComponents类，以下是示例代码：

- (void)testCalendar
{
    NSDate *date = [NSDate date];
    NSCalendar* calendar = [NSCalendar currentCalendar];
    NSDateComponents* components = [calendar components:NSYearCalendarUnit|NSMonthCalendarUnit|NSDayCalendarUnit|NSWeekdayCalendarUnit fromDate:date];
    
    int month = [components month];
    int day = [components day];
    int year = [components year];
    int weekDay = [components weekday];
    
    NSLog(@"week day: %i", weekDay);
    NSLog(@"month: %i", month);
    NSLog(@"day: %i", day);
    NSLog(@"year: %i", year);
}