OC系列foundation Kit基础－NSDate

一.获取当前时间

1.1创建一个日期对象

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

　　输出结果：

2016-07-01 17:31:02.410 OCString[907:402963] 2016-07-01 09:31:02 +0000    //因为时区不一样，需要格式化为本地时间
Program ended with exit code: 0

1.2将时间格式化为本地时间

        //日前格式化
        NSDateFormatter *formatter = [[NSDateFormatter alloc]init];
        //设置日期格式化对象的两个属性
        formatter.dateStyle = NSDateFormatterShortStyle;
        formatter.timeStyle = NSDateFormatterShortStyle;
        NSString *result = [formatter stringFromDate:date];
        NSLog(@"%@",result);

　　输出结果：

2016-07-01 17:36:20.719 OCString[917:424185] 16/7/1 17:36
Program ended with exit code: 0

二.获取当月一共有多少天

 2.1创建一个日期对象

NSDate *date = [NSDate date];

2.2获取系统提供的日历对象

        //获取系统提供的日历对象
        NSCalendar *calender = [NSCalendar currentCalendar];

2.3获取当月第一天和最后一天

        NSRange range = [calender rangeOfUnit:NSCalendarUnitDay inUnit:NSCalendarUnitMonth forDate:date];
        NSLog(@"%@",NSStringFromRange(range));

　　输出结果：

2016-07-01 17:46:21.526 OCString[947:466115] {1, 31}
Program ended with exit code: 0

三.获取当年一共有多少天

同上二中的方法

四.获取当月第一天和最后一天是星期几

 4.1获取当月第一天是星期几

NSDate *date = [NSDate date];

 4.2获取系统提供的日历对象

  NSCalendar *calender = [NSCalendar currentCalendar];　

 4.3获取当月第一天和最后一天

NSRange range = [calender rangeOfUnit:NSCalendarUnitDay inUnit:NSCalendarUnitMonth forDate:date];

 4.4获取当天时间的日期值

NSDateComponents *todayComp = [calender components:NSCalendarUnitDay | NSCalendarUnitMonth | NSCalendarUnitYear fromDate:date];

 4.5计算第一天的日期   

        NSDateComponents *startComp = [todayComp copy];
        startComp.day = range.location;　

 4.6计算最后一天的日期    

        NSDateComponents *endComp = [todayComp copy];
        endComp.day = range.length;

  4.7日期转为时间对象

        NSDate *startDate = [calender dateFromComponents:startComp];
        NSDate *endDate = [calender dateFromComponents:endComp];

   4.8计算星期几

        NSInteger start_week = [calender ordinalityOfUnit:NSCalendarUnitWeekday inUnit:NSCalendarUnitWeekOfYear forDate:startDate];
        NSInteger end_week = [calender ordinalityOfUnit:NSCalendarUnitWeekday inUnit:NSCalendarUnitWeekOfYear forDate:endDate];