blocks|key|3362654|text|DateTime?+d=null;
DateTime+d2;
bool+success+=+DateTime.TryParse("some+date+text",+out+d2);
if+(success)+d=d2;|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|3362655|(可能有更优雅的解决方案，但为什么不简单地执行上面的操作呢？)|unstyled|3362656|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|J|8|@]|9|@]|A|$]]|$1|G|3|-4|5|F|7|K|8|@]|9|@]|A|$]]]|H|$]]

<pre><code>DateTime? d=null;
DateTime d2;
bool success = DateTime.TryParse("some date text", out d2);
if (success) d=d2;
</code></pre>

(There might be more elegant solutions, but why don't you simply do something as above?)

blocks|key|361096|text|正如Jason所说，您可以创建一个正确类型的变量并传递该变量。您可能希望将其封装在您自己的方法中：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|361097|public+static+DateTime?+TryParse(string+text)
{
++++DateTime+date;
++++if+(DateTime.TryParse(text,+out+date))
++++{
++++++++return+date;
++++}
++++else
++++{
++++++++return+null;
++++}
}|code-block|syntax|javascript|361098|..。或者，如果您喜欢条件运算符：|361099|public+static+DateTime?+TryParse(string+text)
{
++++DateTime+date;
++++return+DateTime.TryParse(text,+out+date)+?+date+:+(DateTime?)+null;
}|361100|或在C#+7中：|361101|public+static+DateTime?+TryParse(string+text)+=>
++++DateTime.TryParse(text,+out+var+date)+?+date+:+(DateTime?)+null;|361102|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|U|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

As Jason says, you can create a variable of the right type and pass that. You might want to encapsulate it in your own method:

<pre><code>public static DateTime? TryParse(string text)
{
 DateTime date;
 if (DateTime.TryParse(text, out date))
 {
 return date;
 }
 else
 {
 return null;
 }
}
</code></pre>

... or if you like the conditional operator:

<pre><code>public static DateTime? TryParse(string text)
{
 DateTime date;
 return DateTime.TryParse(text, out date) ? date : (DateTime?) null;
}
</code></pre>

Or in C# 7:

<pre><code>public static DateTime? TryParse(string text) =&gt;
 DateTime.TryParse(text, out var date) ? date : (DateTime?) null;
</code></pre>

blocks|key|3362778|text|以下是Jason建议的略微简明的版本：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3362779|DateTime?+d;+DateTime+dt;
d+=+DateTime.TryParse(DateTime.Now.ToString(),+out+dt)?+dt+:+(DateTime?)null;|code-block|syntax|javascript|3362780|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Here is a slightly concised edition of what Jason suggested:

<pre><code>DateTime? d; DateTime dt;
d = DateTime.TryParse(DateTime.Now.ToString(), out dt)? dt : (DateTime?)null;
</code></pre>

blocks|key|3362757|text|您不能这样做，因为Nullable<DateTime>是与DateTime不同的类型。您需要编写自己的函数来执行此操作，|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3362758|public+bool+TryParse(string+text,+out+Nullable<DateTime>+nDate)
{
++++DateTime+date;
++++bool+isParsed+=+DateTime.TryParse(text,+out+date);
++++if+(isParsed)
++++++++nDate+=+new+Nullable<DateTime>(date);
++++else
++++++++nDate+=+new+Nullable<DateTime>();
++++return+isParsed;
}|code-block|syntax|javascript|3362759|希望这能有所帮助:)|3362760|此编辑：删除了(显然)未正确测试的扩展方法，因为(正如一些糟糕的胡说所指出的那样)试图更改“”参数的扩展方法将不适用于值类型。|BOLD|3362761|附注:问题中的坏胡尔是一位老朋友:)|3362762|entityMap^0|9|I|T|8|0|0|0|1A|H|0|0|I|0^^$0|@$1|2|3|4|5|6|7|T|8|@$9|U|A|V|B|C]|$9|W|A|X|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|Y|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|Z|8|@]|D|@]|E|$]]|$1|M|3|N|5|6|7|10|8|@$9|11|A|12|B|O]]|D|@]|E|$]]|$1|P|3|Q|5|6|7|13|8|@$9|14|A|15|B|O]]|D|@]|E|$]]|$1|R|3|-4|5|6|7|16|8|@]|D|@]|E|$]]]|S|$]]

You can't because <code>Nullable&lt;DateTime&gt;</code> is a different type to <code>DateTime</code>.
You need to write your own function to do it, 

<pre><code>public bool TryParse(string text, out Nullable&lt;DateTime&gt; nDate)
{
 DateTime date;
 bool isParsed = DateTime.TryParse(text, out date);
 if (isParsed)
 nDate = new Nullable&lt;DateTime&gt;(date);
 else
 nDate = new Nullable&lt;DateTime&gt;();
 return isParsed;
}
</code></pre>

Hope this helps :)

EDIT:
Removed the (obviously) improperly tested extension method, because (as Pointed out by some bad hoor) extension methods that attempt to change the "this" parameter will not work with Value Types.

P.S. The Bad Hoor in question is an old friend :)

blocks|key|3362789|text|创建一个扩展方法怎么样？|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3362790|public+static+class+NullableExtensions
{
++++public+static+bool+TryParse(this+DateTime?+dateTime,+string+dateString,+out+DateTime?+result)
++++{
++++++++DateTime+tempDate;
++++++++if(!+DateTime.TryParse(dateString,out+tempDate))
++++++++{
++++++++++++result+=+null;
++++++++++++return+false;
++++++++}

++++++++result+=+tempDate;
++++++++return+true;

++++}
}|code-block|syntax|javascript|3362791|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

What about creating an extension method?

<pre><code>public static class NullableExtensions
{
 public static bool TryParse(this DateTime? dateTime, string dateString, out DateTime? result)
 {
 DateTime tempDate;
 if(! DateTime.TryParse(dateString,out tempDate))
 {
 result = null;
 return false;
 }

 result = tempDate;
 return true;

 }
}
</code></pre>

blocks|key|3149908|text|我不明白为什么微软不处理这个问题。一个聪明的小实用程序方法来处理这个问题(我在int上遇到了这个问题，但是用DateTime替换int会有相同的效果，可能是.....|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3149909|++++public+static+bool+NullableValueTryParse(string+text,+out+int?+nInt)
++++{
++++++++int+value;
++++++++if+(int.TryParse(text,+out+value))
++++++++{
++++++++++++nInt+=+value;
++++++++++++return+true;
++++++++}
++++++++else
++++++++{
++++++++++++nInt+=+null;
++++++++++++return+false;
++++++++}
++++}|code-block|syntax|javascript|3149910|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

I don't see why Microsoft didn't handle this. A smart little utility method to deal with this (I had the issue with int, but replacing int with DateTime will be the same effect, could be.....

<pre><code> public static bool NullableValueTryParse(string text, out int? nInt)
 {
 int value;
 if (int.TryParse(text, out value))
 {
 nInt = value;
 return true;
 }
 else
 {
 nInt = null;
 return false;
 }
 }
</code></pre>

blocks|key|360507|text|这就是你要找的线条：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|360508|DateTime?+d+=+DateTime.TryParse("some+date+text",+out+DateTime+dt)+?+dt+:+null;|code-block|syntax|javascript|360509|如果你想让它成为一个合适的TryParse伪扩展方法，你可以这样做：|360510|public+static+bool+TryParse(string+text,+out+DateTime?+dt)
{
++++if+(DateTime.TryParse(text,+out+DateTime+date))
++++{
++++++++dt+=+date;
++++++++return+true;
++++}
++++else
++++{
++++++++dt+=+null;
++++++++return+false;
++++}
}|360511|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

This is the one liner you're looking for:
<pre><code>DateTime? d = DateTime.TryParse(&quot;some date text&quot;, out DateTime dt) ? dt : null;
</code></pre>
If you want to make it a proper TryParse pseudo-extension method, you can do this:
<pre><code>public static bool TryParse(string text, out DateTime? dt)
{
 if (DateTime.TryParse(text, out DateTime date))
 {
 dt = date;
 return true;
 }
 else
 {
 dt = null;
 return false;
 }
}
</code></pre>

blocks|key|363814|text|下面是一个单行解决方案：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|363815|DateTime?+d+=+DateTime.TryParse("text",+out+DateTime+parseDate)+?+parseDate+:+(DateTime?)null;|code-block|syntax|javascript|363816|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Here's a single line solution:

<pre class="lang-cs prettyprint-override"><code>DateTime? d = DateTime.TryParse("text", out DateTime parseDate) ? parseDate : (DateTime?)null;
</code></pre>

blocks|key|3149953|text|或者，如果您不关心可能引发的异常，可以更改解析的TryParse：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3149954|DateTime?+d+=+DateTime.Parse("some+valid+text");|code-block|syntax|javascript|3149955|尽管也没有布尔值来表示成功，但在某些情况下，如果您知道输入文本总是有效的，那么它可能很实用。|3149956|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

Alternatively, if you are not concerned with the possible exception raised, you could change TryParse for Parse:

<pre><code>DateTime? d = DateTime.Parse("some valid text");
</code></pre>

Although there won't be a boolean indicating success either, it could be practical in some situations where you know that the input text will always be valid.

I want to use the DateTime.TryParse method to get the datetime value of a string into a Nullable. But when I try this:

<pre><code>DateTime? d;
bool success = DateTime.TryParse("some date text", out (DateTime)d);
</code></pre>

the compiler tells me 

<blockquote>
 'out' argument is not classified as a variable
</blockquote>

Not sure what I need to do here. I've also tried: 

<pre><code>out (DateTime)d.Value 
</code></pre>

and that doesn't work either. Any ideas?

How do I use DateTime.TryParse with a Nullable<DateTime>?

编译器

我想使用DateTime.TryParse方法将字符串的datetime值放入一个Nullable中。但是当我尝试这个的时候：DateTime? d;bool success = DateTime.TryParse("some date text", out (DateTime)d);编译器告诉我 'out‘参数未分类为变量不知道我需要在这里做什么。我也尝试过：out (DateTime)d.Va

问如何通过Nullable<DateTime>使用DateTime.TryParse？
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问如何通过Nullable<DateTime>使用DateTime.TryParse？EN

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问如何通过Nullable<DateTime>使用DateTime.TryParse？
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