blocks|key|718599|text|首先，Nullable<T>是一个结构，所以没有这样的对象。您不能调用GetType()，因为这会将值装箱(此时您要么得到null，从而得到一个异常，要么得到一个装箱的不可为空的值，因此不是您想要的类型)。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|718600|(装箱是造成断言混乱的原因--我假设IsType接受object。)|718601|但是，您可以使用类型推断来获取变量的类型作为类型参数：|718602|public+bool+IsNullable<T>(T+value)
{
++++return+Nullable.GetUnderlyingType(typeof(T))+!=+null;
}|code-block|syntax|javascript|718603|当您知道编译时的确切类型时，这并不是很有用，但它对泛型很有用。(当然，还有实现它的替代方法。)|718604|你的真实生活情况是什么？我假设这不是一个这样的断言，因为您在编译时就知道了这个问题的答案。|718605|entityMap^0|3|B|Z|9|0|I|6|Q|6|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]|$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|Z|8|@$9|10|A|11|B|C]|$9|12|A|13|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|14|8|@]|D|@]|E|$]]|$1|J|3|K|5|L|7|15|8|@]|D|@]|E|$M|N]]|$1|O|3|P|5|6|7|16|8|@]|D|@]|E|$]]|$1|Q|3|R|5|6|7|17|8|@]|D|@]|E|$]]|$1|S|3|-4|5|6|7|18|8|@]|D|@]|E|$]]]|T|$]]

Well firstly, <code>Nullable&lt;T&gt;</code> is a struct, so there isn't an object as such. You can't call <code>GetType()</code>, as that will box the value (at which point you either get null and thus an exception, or a boxed non-nullable value and therefore not the type you want).

(Boxing is what's messing up your assertion here - I would assume that <code>IsType</code> accepts <code>object</code>.)

You can use type inference though to get the type of the variable as a type parameter:

<pre><code>public bool IsNullable&lt;T&gt;(T value)
{
 return Nullable.GetUnderlyingType(typeof(T)) != null;
}
</code></pre>

That's not a huge amount of use when you know the exact type at compile-time as in your example, but it's useful for generics. (There are alternative ways of implementing it, of course.)

What's your real life situation? I assume it's not an assertion like this, given that you know the answer to this one at compile time.

blocks|key|718733|text|我喜欢@jon-skeet的答案，但它只有在你知道你要测试的类型的情况下才有效。在我们的世界中，我们使用反射来打开对象并根据正则表达式测试值。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|718734|简化扩展，使其适用于任何类型，对我们来说效果更好。|718735|public+static+bool+IsNullable(this+Type+type)
{
++++return+Nullable.GetUnderlyingType(type)+!=+null;
}|code-block|syntax|javascript|718736|泛型是生命的血液，但有时...:)|718737|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|O|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

I like the @jon-skeet answer but it only works if you know the type you are testing against. In our world we are using reflection to open up objects and test values against regex expressions.

simplifying the extension to work for any type worked better for us.

<pre><code>public static bool IsNullable(this Type type)
{
 return Nullable.GetUnderlyingType(type) != null;
}
</code></pre>

generics are life's blood but sometimes... :)

blocks|key|4412040|text|int?+i+=+0;
var+type+=+TypedReference.GetTargetType(__makeref(i));
var+isNullable+=+type.IsGenericType+&&
++++type.GetGenericTypeDefinition()+==+typeof(Nullable<>);|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|4412041|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>int? i = 0;
var type = TypedReference.GetTargetType(__makeref(i));
var isNullable = type.IsGenericType &amp;&amp;
 type.GetGenericTypeDefinition() == typeof(Nullable&lt;&gt;);
</code></pre>

blocks|key|718615|text|Assert在哪个名称空间中？|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|718616|如您所料，下面的代码返回true：|718617|int?+wtf+=+0;
if+(typeof(Nullable<int>).IsInstanceOfType(wtf))
{
++++//+Do+things
}|code-block|syntax|javascript|718618|尽管值得注意的是，typeof(Nullable<int>).IsInstanceOfType(42)也返回true+-这是因为该方法接受object，因此被包装为Nullable<int>。|718619|entityMap^0|0|6|0|C|4|0|0|9|16|1X|6|2A|D|0^^$0|@$1|2|3|4|5|6|7|Q|8|@$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|T|8|@$9|U|A|V|B|C]]|D|@]|E|$]]|$1|H|3|I|5|J|7|W|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|X|8|@$9|Y|A|Z|B|C]|$9|10|A|11|B|C]|$9|12|A|13|B|C]]|D|@]|E|$]]|$1|O|3|-4|5|6|7|14|8|@]|D|@]|E|$]]]|P|$]]

What namespace is <code>Assert</code> in?

The following returns <code>true</code> as you would expect:

<pre><code>int? wtf = 0;
if (typeof(Nullable&lt;int&gt;).IsInstanceOfType(wtf))
{
 // Do things
}
</code></pre>

Although its worth noting that <code>typeof(Nullable&lt;int&gt;).IsInstanceOfType(42)</code> also returns true - this is because this method accepts an <code>object</code> and so gets boxed as a <code>Nullable&lt;int&gt;</code>.

blocks|key|2337180|text|这是我想出来的，因为其他一切似乎都失败了-至少在使用>=+C#+6的可移植类库/+DotNet核心上是这样|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2337181|基本上，您扩展泛型类型Object和Nullable<T>，并利用与底层类型匹配的静态扩展方法将被调用这一事实，并且优先于泛型T扩展方法。|offset|length|style|CODE|2337182|public+static+partial+class+ObjectExtension
{
++++public+static+bool+IsNullable<T>(this+T+self)
++++{
++++++++return+false;
++++}
}|code-block|syntax|javascript|2337183|一个用于Nullable<T>|2337184|public+static+partial+class+NullableExtension
{
++++public+static+bool+IsNullable<T>(this+Nullable<T>+self)+where+T+:+struct
++++{
++++++++return+true;
++++}
}|2337185|使用反射、type.IsGeneric和type.GetGenericParameters()在我当前的.NET运行时集上不起作用。|2337186|entityMap^0|0|B|6|I|B|1R|1|0|0|4|B|0|0|5|E|K|R|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|V|8|@$D|W|E|X|F|G]|$D|Y|E|Z|F|G]|$D|10|E|11|F|G]]|9|@]|A|$]]|$1|H|3|I|5|J|7|12|8|@]|9|@]|A|$K|L]]|$1|M|3|N|5|6|7|13|8|@$D|14|E|15|F|G]]|9|@]|A|$]]|$1|O|3|P|5|J|7|16|8|@]|9|@]|A|$K|L]]|$1|Q|3|R|5|6|7|17|8|@$D|18|E|19|F|G]|$D|1A|E|1B|F|G]]|9|@]|A|$]]|$1|S|3|-4|5|6|7|1C|8|@]|9|@]|A|$]]]|T|$]]

Here is what I came up with, as everything else seemed to fail - at least on Portable Class Library / DotNet Core with >= C# 6

Basically you extend generic Type <code>Object</code> and <code>Nullable&lt;T&gt;</code> and use the fact that the static extension method that matches the underlying type is going to be invoked and takes precedence over the generic <code>T</code> extension-method.

<pre><code>public static partial class ObjectExtension
{
 public static bool IsNullable&lt;T&gt;(this T self)
 {
 return false;
 }
}
</code></pre>

and one for <code>Nullable&lt;T&gt;</code>

<pre><code>public static partial class NullableExtension
{
 public static bool IsNullable&lt;T&gt;(this Nullable&lt;T&gt; self) where T : struct
 {
 return true;
 }
}
</code></pre>

Using Reflection and <code>type.IsGeneric</code> and <code>type.GetGenericParameters()</code> did not work on my current set of .NET Runtimes.

blocks|key|2621166|text|这对我很有效，希望你也能。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2621167|public+static+bool+IsNullable(this+Type+type)
{
++++return+Nullable.GetUnderlyingType(type)+!=+null;
}|code-block|syntax|javascript|2621168|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|$]]

It works fo me, hope for you too.
<pre><code>public static bool IsNullable(this Type type)
{
 return Nullable.GetUnderlyingType(type) != null;
}
</code></pre>

blocks|key|4412202|text|基于Vladimir+answer|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|4412203|public+static+class+GenericExtensions
{
+++public+static+bool+IsNullable<T>(this+T+item)+=>
+++++TypedReference.GetTargetType(__makeref(item)).FullName.Contains("System.Nullable");
}|code-block|syntax|javascript|4412204|用法：|4412205|int?+nullableInt+=+42;
bool+nIntIsNullable+=+nullableInt.IsNullable();|4412206|持续时间:机器平均持续时间<2ms。|4412207|备注：|style|BOLD|4412208|4412209|Important,+this+API+is+not+CLS-compliant.|unordered-list-item|4412210|Contains("System.Nullable")可以说得更具体。|CODE|4412211|4412212|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/a/21780367/7678085|1|https://docs.microsoft.com/en-us/dotnet/api/system.typedreference?view=net-6.0^0|B|6|0|0|0|0|0|0|0|3|0|0|0|15|1|0|0|R|0|0^^$0|@$1|2|3|4|5|6|7|1A|8|@]|9|@$A|1B|B|1C|1|1D]]|C|$]]|$1|D|3|E|5|F|7|1E|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|1F|8|@]|9|@]|C|$]]|$1|K|3|L|5|F|7|1G|8|@]|9|@]|C|$G|H]]|$1|M|3|N|5|6|7|1H|8|@]|9|@]|C|$]]|$1|O|3|P|5|6|7|1I|8|@$A|1J|B|1K|Q|R]]|9|@]|C|$]]|$1|S|3|-4|5|6|7|1L|8|@]|9|@]|C|$]]|$1|T|3|U|5|V|7|1M|8|@]|9|@$A|1N|B|1O|1|1P]]|C|$]]|$1|W|3|X|5|V|7|1Q|8|@$A|1R|B|1S|Q|Y]]|9|@]|C|$]]|$1|Z|3|-4|5|6|7|1T|8|@]|9|@]|C|$]]|$1|10|3|-4|5|6|7|1U|8|@]|9|@]|C|$]]]|11|$12|$5|13|14|15|C|$16|17]]|18|$5|13|14|15|C|$16|19]]]]

Based on Vladimir <a href="https://stackoverflow.com/a/21780367/7678085">answer</a>:
<pre><code>public static class GenericExtensions
{
 public static bool IsNullable&lt;T&gt;(this T item) =&gt;
 TypedReference.GetTargetType(__makeref(item)).FullName.Contains(&quot;System.Nullable&quot;);
}
</code></pre>
Usage:
<pre><code>int? nullableInt = 42;
bool nIntIsNullable = nullableInt.IsNullable();
</code></pre>
Duration: &lt;2ms on average machine.
Remarks:
<ul>
<li><a href="https://docs.microsoft.com/en-us/dotnet/api/system.typedreference?view=net-6.0" rel="nofollow noreferrer">Important, this API is not CLS-compliant.</a></li>
<li><code>Contains(&quot;System.Nullable&quot;)</code> can be more specific.</li>
</ul>

Surprisingly the following code fails the Assert:

<pre><code>int? wtf = 0;
Assert.IsType&lt;Nullable&lt;int&gt;&gt;(wtf);
</code></pre>

So just out curiosity, how can you determine if a given instance is a Nullable&lt;> object or not?

Detecting a Nullable Type via reflection

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

文章

问答

视频

学习中心

腾讯云实验室

直播

竞赛

腾讯云代码分析专区

腾讯iOA零信任安全管理系统专区

腾讯云架构师技术同盟交流圈

腾讯云数据库专区

腾讯云顾问专区

腾讯云原生专区

腾讯混元专区

腾讯云TCE专区

腾讯云Lighthouse专区

腾讯云HAI专区

腾讯云Edgeone专区

腾讯云存储专区

腾讯云智能专区

腾讯轻联专区 

腾讯云开发专区

TAPD专区

腾讯轻量云游戏服专区

腾讯云最具价值专家

腾讯云架构师技术同盟

腾讯云创作之星

腾讯云开发者先锋

腾讯云代码助手

云原生构建

TAPD 敏捷项目管理

Cloud Studio

SDK中心

API中心

命令行工具

涵盖代码开发、场景应用、自动测试全流程，助你从零构建专属AI助手

一站式MCP教程库，解锁AI应用新玩法

令人惊讶的是，以下代码无法执行断言：int? wtf = 0;Assert.IsType<Nullable<int>>(wtf);出于好奇，您如何确定给定的实例是否为Nullable<>对象？

问通过反射检测可为Nullable的类型
EN

回答 7

Stack Overflow用户

Stack Overflow用户

Stack Overflow用户

社区

活动

圈层

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问通过反射检测可为Nullable的类型EN

回答 7

Stack Overflow用户

Stack Overflow用户

Stack Overflow用户

社区

活动

圈层

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问通过反射检测可为Nullable的类型
EN