C# 从日期时间中减去天数
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Subtract days from a DateTime
提问by Buena
I have the following code in my C# program.
我的 C# 程序中有以下代码。
DateTime dateForButton = DateTime.Now;
dateForButton = dateForButton.AddDays(-1); // ERROR: un-representable DateTime
Whenever I run it, I get the following error:
每当我运行它时，都会出现以下错误：
The added or subtracted value results in an un-representable DateTime.
Parameter name: value
添加或减去的值会导致无法表示的 DateTime。
参数名称：值
Iv'e never seen this error message before, and don't understand why I'm seeing it. From the answers Iv'e read so far, I'm lead to believe that I can use -1 in an add operation to subtract days, but as my question shows this is not the case for what I'm attempting to do.
我以前从未见过此错误消息，也不明白为什么我会看到它。从到目前为止我读到的答案中，我相信我可以在加法运算中使用 -1 来减去天数，但正如我的问题所显示的那样，我尝试做的事情并非如此。
采纳答案by CyberDude
That error usually occurs when you try to subtract an interval from DateTime.MinValueor you want to add something to DateTime.MaxValue(or you try to instantiate a date outside this min-max interval). Are you sure you're not assigning MinValuesomewhere?
该错误通常发生在您尝试从中减去一个间隔DateTime.MinValue或想要添加某些内容DateTime.MaxValue（或者您尝试实例化此最小-最大间隔之外的日期）时。你确定你不是在分配MinValue某个地方吗？
回答by Rajesh Subramanian
You can use the following code:
您可以使用以下代码：
dateForButton = dateForButton.Subtract(TimeSpan.FromDays(1));
回答by christiandev
DateTime dateForButton = DateTime.Now.AddDays(-1);
回答by sam
You can do:
你可以做：
DateTime.Today.AddDays(-1)
回答by Mark Benson
The object (i.e. destination variable) for the AddDays method can't be the same as the source.
AddDays 方法的对象（即目标变量）不能与源相同。
Instead of:
代替：
DateTime today = DateTime.Today;
today.AddDays(-7);
Try this instead:
试试这个：
DateTime today = DateTime.Today;
DateTime sevenDaysEarlier = today.AddDays(-7);
回答by cahit beyaz
The dateTime.AddDays(-1)does not subtract that one day from the dateTimereference. It will return a new instance, with that one day subtracted from the original reference.
在dateTime.AddDays(-1)不减去一天，有一个dateTime参考。它将返回一个新实例，从原始引用中减去这一天。
DateTime dateTime = DateTime.Now;
DateTime otherDateTime = dateTime.AddDays(-1);
回答by Ainsley Hobart
Using AddDays(-1)worked for me until I tried to cross months. When I tried to subtract 2 days from 2017-01-01 the result was 2016-00-30. It could not handle the month change correctly (though the year seemed to be fine).
使用AddDays(-1)对我有用，直到我试图跨越几个月。当我尝试从 2017-01-01 减去 2 天时，结果是 2016-00-30。它无法正确处理月份变化（尽管年份似乎很好）。
I used date = Convert.ToDateTime(date).Subtract(TimeSpan.FromDays(2)).ToString("yyyy-mm-dd");and have no issues.
我用过date = Convert.ToDateTime(date).Subtract(TimeSpan.FromDays(2)).ToString("yyyy-mm-dd");，没有问题。
回答by UsernameNotFound
I've had issues using AddDays(-1).
我在使用AddDays(-1) 时遇到了问题。
My solution is TimeSpan.
我的解决方案是TimeSpan。
DateTime.Now - TimeSpan.FromDays(1);
回答by Sambhav jain
Instead of directly decreasing number of days from the date object directly, first get date value then subtract days. See below example:
不是直接从日期对象中直接减少天数，而是先获取日期值然后减去天数。见下面的例子：
DateTime SevenDaysFromEndDate = someDate.Value.AddDays(-1);
Here, someDate is a variable of type DateTime.
这里，someDate 是一个 DateTime 类型的变量。
