为什么日期时间改变到16年前的1月1日不正确显示年份？ [英] why datetime change to 1st Jan in 16 year ago does not show year part properly?

问题描述

我想将日期从今天的日期开始到1月16日的1日。我使用代码

i want to set the date to 1st of Jan 16 years ago from today's date. I used the code

DateTime dtm = new DateTime(DateTime.Today.Year, 1, 1);
dtm.AddYears(-16);
dtpDOB.Value = dtm;// assign value to date time picker

但它显示日期值为1/1/2014，为什么这不会在16年内设定年份？

but it shows the date value as 1/1/2014, why this does not set the year part back in 16 years?

谢谢

推荐答案

DateTime type是一个 struct 。因此，其属性是 immutable （它们不能被修改后的构造函数）。在C＃中通过按值传递结构。

The DateTime type is a struct. Because of that, its properties are immutable (they can't be changed post-constructor). structs are passed by value in C#.

正如其他几个人所说，您需要重新分配价值。

Because of that, as a few other people have said, you need to reassign the value.

dtm = dtm.AddYears(-16);

这就像一个典型的字符串操作C＃。当您调用 string.Replace（string，string）时，需要捕获该操作的返回值。对于LINQ-y IEnumerable< T> 操作也是如此。

It's just like a typical string operation in C#. When you call string.Replace(string, string), you need to capture the return value of the operation. The same is true for LINQ-y IEnumerable<T> operations.

虽然说，看起来像你最好是适当调用构造函数。

Although that said, it seems like you'd be better off to just call the constructor appropriately.

dtpDOB.Value = new DateTime(DateTime.Today.Year - 16, 1, 1);

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