设置里面设置时区会有错误-----需要设置setFirstWeekday：
NSCalendar *calendar = [NSCalendar currentCalendar];
[calendar setFirstWeekday:1];//1.Sun. 2.Mon. 3.Thes. 4.Wed. 5.Thur. 6.Fri. 7.Sat.
-
(NSInteger)firstWeekDayInMonth{
NSCalendar *calendar = [NSCalendar currentCalendar];
[calendar setFirstWeekday:1];//1.Sun. 2.Mon. 3.Thes. 4.Wed. 5.Thur. 6.Fri. 7.Sat.
NSDateComponents *comp = [calendar components:(NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay) fromDate:self];
[comp setDay:1];
NSDate *firstDayOfMonthDate = [calendar dateFromComponents:comp];NSUInteger firstWeekday = [calendar ordinalityOfUnit:NSCalendarUnitWeekday inUnit:NSCalendarUnitWeekOfMonth forDate:firstDayOfMonthDate] - 1;
return firstWeekday;
}
