C# 如何检查DateTime是否为空
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/9249769/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
How to check if DateTime is null
提问by user1202765
I have my two DateTimeas follow:
我有我的两个DateTime如下：
DateTime startDate = CalendarFrom.SelectedDate;
DateTime endDate = CalendarTo.SelectedDate;
Now, I want to check if the startDateand endDateis selected or not. As I know, we cannot assign null to DateTimeso I write in this way:
现在，我想检查startDate和endDate是否被选中。据我所知，我们不能为 null 赋值，DateTime所以我这样写：
if (startDate == DateTime.MinValue && endDate == DateTime.MinValue)
{
// actions here
}
However I realise that for the endDate, it is not "1/1/0001 12:00:00 AM" so it cannot be checked by using DateTime.MinValue.
但是我意识到对于endDate，它不是“1/1/0001 12:00:00 AM”，因此无法使用DateTime.MinValue.
I would like to know how will I be able to do checking for the endDate. Thanks!
我想知道如何检查endDate. 谢谢！
回答by Jon Skeet
A DateTimeitself can't be null - it's cleanest to use DateTime?aka Nullable<DateTime>to represent nullable values.
ADateTime本身不能为空 - 使用DateTime?akaNullable<DateTime>来表示可空值是最干净的。
It's not clear what CalendarFromand CalendarToare, but they may not support Nullable<DateTime>themselves - but it would be a good idea to centralize the conversion here so you can use Nullable<DateTime>everywhere otherthan where you're directly using CalendarFromand CalendarTo.
目前还不清楚是什么CalendarFrom和CalendarTo，但它们可能不支持Nullable<DateTime>自己-但是这将是一个好主意，这里集中了转换，所以你可以使用Nullable<DateTime>随处其他比你在哪里使用直接CalendarFrom和CalendarTo。
回答by shiva
I am not sure what are your CalenderFrom and CalenderTo are; but I am assuming that they are static classess. Based on that assumption, this is how I would write this code.
我不确定你的 CalenderFrom 和 CalenderTo 是什么；但我假设它们是静态类。基于这个假设，这就是我编写这段代码的方式。
public static class CalendarFrom
{
public static DateTime SelectedFrom { get; set; }
}
public static class CalendarTo
{
public static DateTime SelectedDate { get; set; }
}
DateTime? startDate = CalendarFrom.SelectedFrom;
DateTime? endDate = CalendarTo.SelectedDate;
if (startDate.HasValue
&& ( startDate.Value != DateTime.MaxValue || startDate.Value != DateTime.MinValue))
{
}
回答by Jonathan Wood
DateTimeis a struct and so it can never be null.
DateTime是一个结构体，所以它永远不能为空。
I can think of two options:
我能想到两个选择：
If you really want to support null, use
DateTime?to create a nullable DateTime.Alternatively, it may be appropriate in your application to simply set a
DateTimevalue to a default value that indicates no real value has been set. For this default value, you could use eitherdefault(DateTime)or something likeDateTime.MinValue.
如果您真的想支持 null，请使用
DateTime?创建一个可为 null 的 DateTime。或者，在您的应用程序中简单地将一个
DateTime值设置为默认值可能是合适的，该值指示尚未设置实际值。对于这个默认值，可以使用两种default(DateTime)或类似的东西DateTime.MinValue。
