错误的星期几?

我正在试着得到每月第一天的周指数。但它返回了错误的值。我期待2(星期一),但结果是6(星期五)。也许我错过了什么。

NSDateComponents *dateComponents = [[NSDateComponents alloc] init];
[dateComponents setDay:1];
[dateComponents setMonth:1];
[dateComponents setYear:2016];

NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSCalendarIdentifierGregorian];
NSDate *date = [calendar dateFromComponents:dateComponents];

long weekDay = [calendar component:(NSCalendarUnitWeekday) fromDate:date];