blocks|key|1397945|text|是的，完全正确。使用反射：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1397946|static+IEnumerable<Type>+GetTypesWithHelpAttribute(Assembly+assembly)+{
++++foreach(Type+type+in+assembly.GetTypes())+{
++++++++if+(type.GetCustomAttributes(typeof(HelpAttribute),+true).Length+>+0)+{
++++++++++++yield+return+type;
++++++++}
++++}
}|code-block|syntax|javascript|1397947|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|$]]

Yes, absolutely. Using Reflection:

<pre><code>static IEnumerable&lt;Type&gt; GetTypesWithHelpAttribute(Assembly assembly) {
 foreach(Type type in assembly.GetTypes()) {
 if (type.GetCustomAttributes(typeof(HelpAttribute), true).Length &gt; 0) {
 yield return type;
 }
 }
}
</code></pre>

blocks|key|1398058|text|那么，您将不得不枚举加载到当前应用程序域中的所有程序集中的所有类。为此，您需要在当前应用程序域的AppDomain实例上调用GetAssemblies+method。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1398059|在那里，您可以在每个Assembly上调用GetExportedTypes+(如果只想要公共类型)或GetTypes来获取程序集中包含的类型。|1398060|然后，在每个Type实例上调用GetCustomAttributes+extension+method，传递要查找的属性的类型。|1398061|您可以使用LINQ为您简化此过程：|1398062|var+typesWithMyAttribute+=
++++from+a+in+AppDomain.CurrentDomain.GetAssemblies()
++++from+t+in+a.GetTypes()
++++let+attributes+=+t.GetCustomAttributes(typeof(HelpAttribute),+true)
++++where+attributes+!=+null+&&+attributes.Length+>+0
++++select+new+{+Type+=+t,+Attributes+=+attributes.Cast<HelpAttribute>()+};|code-block|syntax|javascript|1398063|上面的查询将获得应用了属性的每个类型，以及分配给它的属性的实例。|1398064|请注意，如果将大量程序集加载到应用程序域中，则该操作的开销可能会很大。您可以使用Parallel+LINQ来减少操作时间(以CPU周期为代价)，如下所示：|1398065|var+typesWithMyAttribute+=
++++//+Note+the+AsParallel+here,+this+will+parallelize+everything+after.
++++from+a+in+AppDomain.CurrentDomain.GetAssemblies().AsParallel()
++++from+t+in+a.GetTypes()
++++let+attributes+=+t.GetCustomAttributes(typeof(HelpAttribute),+true)
++++where+attributes+!=+null+&&+attributes.Length+>+0
++++select+new+{+Type+=+t,+Attributes+=+attributes.Cast<HelpAttribute>()+};|1398066|根据特定的Assembly对其进行过滤非常简单：|1398067|Assembly+assembly+=+...;

var+typesWithMyAttribute+=
++++from+t+in+assembly.GetTypes()
++++let+attributes+=+t.GetCustomAttributes(typeof(HelpAttribute),+true)
++++where+attributes+!=+null+&&+attributes.Length+>+0
++++select+new+{+Type+=+t,+Attributes+=+attributes.Cast<HelpAttribute>()+};|1398068|如果程序集中包含大量类型，则可以再次使用并行LINQ：|1398069|Assembly+assembly+=+...;

var+typesWithMyAttribute+=
++++//+Partition+on+the+type+list+initially.
++++from+t+in+assembly.GetTypes().AsParallel()
++++let+attributes+=+t.GetCustomAttributes(typeof(HelpAttribute),+true)
++++where+attributes+!=+null+&&+attributes.Length+>+0
++++select+new+{+Type+=+t,+Attributes+=+attributes.Cast<HelpAttribute>()+};|1398070|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.microsoft.com/en-us/dotnet/api/system.appdomain|1|https://docs.microsoft.com/en-us/dotnet/api/system.appdomain.getassemblies|2|https://docs.microsoft.com/en-us/dotnet/api/system.reflection.assembly|3|https://docs.microsoft.com/en-us/dotnet/api/system.reflection.assembly.getexportedtypes|4|https://docs.microsoft.com/en-us/dotnet/api/system.reflection.assembly.gettypes|5|https://docs.microsoft.com/en-us/dotnet/api/system.type|6|https://docs.microsoft.com/en-us/dotnet/api/system.reflection.customattributeextensions.getcustomattributes|7|https://docs.microsoft.com/en-us/dotnet/standard/parallel-programming/parallel-linq-plinq^0|1C|9|1Q|D|1C|9|0|1Q|K|1|0|A|8|L|G|1E|8|A|8|2|L|G|3|1E|8|4|0|6|4|F|J|6|4|5|F|10|6|0|0|0|0|14|D|7|0|0|5|8|0|0|0|0^^$0|@$1|2|3|4|5|6|7|1Q|8|@$9|1R|A|1S|B|C]|$9|1T|A|1U|B|C]]|D|@$9|1V|A|1W|1|1X]|$9|1Y|A|1Z|1|20]]|E|$]]|$1|F|3|G|5|6|7|21|8|@$9|22|A|23|B|C]|$9|24|A|25|B|C]|$9|26|A|27|B|C]]|D|@$9|28|A|29|1|2A]|$9|2B|A|2C|1|2D]|$9|2E|A|2F|1|2G]]|E|$]]|$1|H|3|I|5|6|7|2H|8|@$9|2I|A|2J|B|C]|$9|2K|A|2L|B|C]]|D|@$9|2M|A|2N|1|2O]|$9|2P|A|2Q|1|2R]]|E|$]]|$1|J|3|K|5|6|7|2S|8|@]|D|@]|E|$]]|$1|L|3|M|5|N|7|2T|8|@]|D|@]|E|$O|P]]|$1|Q|3|R|5|6|7|2U|8|@]|D|@]|E|$]]|$1|S|3|T|5|6|7|2V|8|@]|D|@$9|2W|A|2X|1|2Y]]|E|$]]|$1|U|3|V|5|N|7|2Z|8|@]|D|@]|E|$O|P]]|$1|W|3|X|5|6|7|30|8|@$9|31|A|32|B|C]]|D|@]|E|$]]|$1|Y|3|Z|5|N|7|33|8|@]|D|@]|E|$O|P]]|$1|10|3|11|5|6|7|34|8|@]|D|@]|E|$]]|$1|12|3|13|5|N|7|35|8|@]|D|@]|E|$O|P]]|$1|14|3|-4|5|6|7|36|8|@]|D|@]|E|$]]]|15|$16|$5|17|18|19|E|$1A|1B]]|1C|$5|17|18|19|E|$1A|1D]]|1E|$5|17|18|19|E|$1A|1F]]|1G|$5|17|18|19|E|$1A|1H]]|1I|$5|17|18|19|E|$1A|1J]]|1K|$5|17|18|19|E|$1A|1L]]|1M|$5|17|18|19|E|$1A|1N]]|1O|$5|17|18|19|E|$1A|1P]]]]

Well, you would have to enumerate through all the classes in all the assemblies that are loaded into the current app domain. To do that, you would call the <a href="https://docs.microsoft.com/en-us/dotnet/api/system.appdomain.getassemblies" rel="noreferrer"><code>GetAssemblies</code> method</a> on the <a href="https://docs.microsoft.com/en-us/dotnet/api/system.appdomain" rel="noreferrer"><code>AppDomain</code></a> instance for the current app domain.
From there, you would call <a href="https://docs.microsoft.com/en-us/dotnet/api/system.reflection.assembly.getexportedtypes" rel="noreferrer"><code>GetExportedTypes</code></a> (if you only want public types) or <a href="https://docs.microsoft.com/en-us/dotnet/api/system.reflection.assembly.gettypes" rel="noreferrer"><code>GetTypes</code></a> on each <a href="https://docs.microsoft.com/en-us/dotnet/api/system.reflection.assembly" rel="noreferrer"><code>Assembly</code></a> to get the types that are contained in the assembly.
Then, you would call the <a href="https://docs.microsoft.com/en-us/dotnet/api/system.reflection.customattributeextensions.getcustomattributes" rel="noreferrer"><code>GetCustomAttributes</code> extension method</a> on each <a href="https://docs.microsoft.com/en-us/dotnet/api/system.type" rel="noreferrer"><code>Type</code></a> instance, passing the type of the attribute you wish to find.
You can use LINQ to simplify this for you:
<pre><code>var typesWithMyAttribute =
 from a in AppDomain.CurrentDomain.GetAssemblies()
 from t in a.GetTypes()
 let attributes = t.GetCustomAttributes(typeof(HelpAttribute), true)
 where attributes != null &amp;&amp; attributes.Length &gt; 0
 select new { Type = t, Attributes = attributes.Cast&lt;HelpAttribute&gt;() };
</code></pre>
The above query will get you each type with your attribute applied to it, along with the instance of the attribute(s) assigned to it.
Note that if you have a large number of assemblies loaded into your application domain, that operation could be expensive. You can use <a href="https://docs.microsoft.com/en-us/dotnet/standard/parallel-programming/parallel-linq-plinq" rel="noreferrer">Parallel LINQ</a> to reduce the time of the operation (at the cost of CPU cycles), like so:
<pre><code>var typesWithMyAttribute =
 // Note the AsParallel here, this will parallelize everything after.
 from a in AppDomain.CurrentDomain.GetAssemblies().AsParallel()
 from t in a.GetTypes()
 let attributes = t.GetCustomAttributes(typeof(HelpAttribute), true)
 where attributes != null &amp;&amp; attributes.Length &gt; 0
 select new { Type = t, Attributes = attributes.Cast&lt;HelpAttribute&gt;() };
</code></pre>
Filtering it on a specific <code>Assembly</code> is simple:
<pre><code>Assembly assembly = ...;

var typesWithMyAttribute =
 from t in assembly.GetTypes()
 let attributes = t.GetCustomAttributes(typeof(HelpAttribute), true)
 where attributes != null &amp;&amp; attributes.Length &gt; 0
 select new { Type = t, Attributes = attributes.Cast&lt;HelpAttribute&gt;() };
</code></pre>
And if the assembly has a large number of types in it, then you can use Parallel LINQ again:
<pre><code>Assembly assembly = ...;

var typesWithMyAttribute =
 // Partition on the type list initially.
 from t in assembly.GetTypes().AsParallel()
 let attributes = t.GetCustomAttributes(typeof(HelpAttribute), true)
 where attributes != null &amp;&amp; attributes.Length &gt; 0
 select new { Type = t, Attributes = attributes.Cast&lt;HelpAttribute&gt;() };
</code></pre>

blocks|key|1398168|text|如前所述，反思是一条可行的道路。如果你打算频繁地调用它，我强烈建议缓存结果，因为反射，特别是枚举每个类，可能会相当慢。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1398169|这是我的代码片段，它遍历所有加载的程序集中的所有类型：|1398170|//+this+is+making+the+assumption+that+all+assemblies+we+need+are+already+loaded.
foreach+(Assembly+assembly+in+AppDomain.CurrentDomain.GetAssemblies())+
{
++++foreach+(Type+type+in+assembly.GetTypes())
++++{
++++++++var+attribs+=+type.GetCustomAttributes(typeof(MyCustomAttribute),+false);
++++++++if+(attribs+!=+null+&&+attribs.Length+>+0)
++++++++{
++++++++++++//+add+to+a+cache.
++++++++}
++++}
}|code-block|syntax|javascript|1398171|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|L|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|M|8|@]|9|@]|A|$G|H]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

As already stated, reflection is the way to go. If you are going to call this frequently, I highly suggest caching the results, as reflection, especially enumerating through every class, can be quite slow.

This is a snippet of my code that runs through all the types in all loaded assemblies:

<pre><code>// this is making the assumption that all assemblies we need are already loaded.
foreach (Assembly assembly in AppDomain.CurrentDomain.GetAssemblies()) 
{
 foreach (Type type in assembly.GetTypes())
 {
 var attribs = type.GetCustomAttributes(typeof(MyCustomAttribute), false);
 if (attribs != null &amp;&amp; attribs.Length &gt; 0)
 {
 // add to a cache.
 }
 }
}
</code></pre>

blocks|key|1612924|text|其他答案参考GetCustomAttributes。添加此示例作为使用IsDefined的示例|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1612925|Assembly+assembly+=+...
var+typesWithHelpAttribute+=+
++++++++from+type+in+assembly.GetTypes()
++++++++where+type.IsDefined(typeof(HelpAttribute),+false)
++++++++select+type;|code-block|syntax|javascript|1612926|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-us/library/88d17d13.aspx|1|http://msdn.microsoft.com/en-us/library/system.attribute.isdefined.aspx^0|6|J|0|Z|9|1|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@$A|T|B|U|1|V]|$A|W|B|X|1|Y]]|C|$]]|$1|D|3|E|5|F|7|Z|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|10|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]|Q|$5|L|M|N|C|$O|R]]]]

Other answers reference <a href="http://msdn.microsoft.com/en-us/library/88d17d13.aspx">GetCustomAttributes</a>. Adding this one as an example of using <a href="http://msdn.microsoft.com/en-us/library/system.attribute.isdefined.aspx">IsDefined</a>

<pre><code>Assembly assembly = ...
var typesWithHelpAttribute = 
 from type in assembly.GetTypes()
 where type.IsDefined(typeof(HelpAttribute), false)
 select type;
</code></pre>

blocks|key|1612959|text|在Portable+.NET+limitations的情况下，以下代码应该可以工作：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1612960|++++public+static+IEnumerable<TypeInfo>+GetAtributedTypes(+Assembly[]+assemblies,+
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++Type+attributeType+)
++++{
++++++++var+typesAttributed+=
++++++++++++from+assembly+in+assemblies
++++++++++++from+type+in+assembly.DefinedTypes
++++++++++++where+type.IsDefined(attributeType,+false)
++++++++++++select+type;
++++++++return+typesAttributed;
++++}|code-block|syntax|javascript|1612961|或者用于大量使用基于循环状态的yield+return的程序集|style|CODE|1612962|++++public+static+IEnumerable<TypeInfo>+GetAtributedTypes(+Assembly[]+assemblies,+
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++Type+attributeType+)
++++{
++++++++foreach+(var+assembly+in+assemblies)
++++++++{
++++++++++++foreach+(var+typeInfo+in+assembly.DefinedTypes)
++++++++++++{
++++++++++++++++if+(typeInfo.IsDefined(attributeType,+false))
++++++++++++++++{
++++++++++++++++++++yield+return+typeInfo;
++++++++++++++++}
++++++++++++}
++++++++}
++++}|1612963|entityMap|0|LINK|mutability|MUTABLE|url|https://blogs.msdn.microsoft.com/dotnet/2016/02/10/porting-to-net-core/^0|1|P|0|0|0|F|C|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@$A|X|B|Y|1|Z]]|C|$]]|$1|D|3|E|5|F|7|10|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|11|8|@$A|12|B|13|K|L]]|9|@]|C|$]]|$1|M|3|N|5|F|7|14|8|@]|9|@]|C|$G|H]]|$1|O|3|-4|5|6|7|15|8|@]|9|@]|C|$]]]|P|$Q|$5|R|S|T|C|$U|V]]]]

In case of the <a href="https://blogs.msdn.microsoft.com/dotnet/2016/02/10/porting-to-net-core/" rel="nofollow">Portable .NET limitations</a>, the following code should work:

<pre><code> public static IEnumerable&lt;TypeInfo&gt; GetAtributedTypes( Assembly[] assemblies, 
 Type attributeType )
 {
 var typesAttributed =
 from assembly in assemblies
 from type in assembly.DefinedTypes
 where type.IsDefined(attributeType, false)
 select type;
 return typesAttributed;
 }
</code></pre>

or for a large number of assemblies using loop-state based <code>yield return</code>:

<pre><code> public static IEnumerable&lt;TypeInfo&gt; GetAtributedTypes( Assembly[] assemblies, 
 Type attributeType )
 {
 foreach (var assembly in assemblies)
 {
 foreach (var typeInfo in assembly.DefinedTypes)
 {
 if (typeInfo.IsDefined(attributeType, false))
 {
 yield return typeInfo;
 }
 }
 }
 }
</code></pre>

blocks|key|1613026|text|这是在已接受的解决方案之上的性能增强。迭代所有的类可能会很慢，因为类太多了。有时，您可以筛选出整个程序集，而不查看其任何类型。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1613027|例如，如果您正在查找自己声明的属性，则不希望任何系统DLL包含具有该属性的任何类型。Assembly.GlobalAssemblyCache属性是检查系统DLL的快捷方法。当我在一个真实的程序上尝试时，我发现我可以跳过30,101个类型，我只需要检查1,983个类型。|1613028|另一种过滤方法是使用Assembly.ReferencedAssemblies。假设您需要具有特定属性的类，并且该属性是在特定程序集中定义的，那么您只关心该程序集和引用它的其他程序集。在我的测试中，这比检查GlobalAssemblyCache属性更有帮助。|1613029|我把这两者结合起来，得到的速度更快。下面的代码包括这两个过滤器。|1613030|++++++++string+definedIn+=+typeof(XmlDecoderAttribute).Assembly.GetName().Name;
++++++++foreach+(Assembly+assembly+in+AppDomain.CurrentDomain.GetAssemblies())
++++++++++++//+Note+that+we+have+to+call+GetName().Name.++Just+GetName()+will+not+work.++The+following
++++++++++++//+if+statement+never+ran+when+I+tried+to+compare+the+results+of+GetName().
++++++++++++if+((!assembly.GlobalAssemblyCache)+&&+((assembly.GetName().Name+==+definedIn)+%7C%7C+assembly.GetReferencedAssemblies().Any(a+=>+a.Name+==+definedIn)))
++++++++++++++++foreach+(Type+type+in+assembly.GetTypes())
++++++++++++++++++++if+(type.GetCustomAttributes(typeof(XmlDecoderAttribute),+true).Length+>+0)|code-block|syntax|javascript|1613031|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|Q|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|R|8|@]|9|@]|A|$]]|$1|H|3|I|5|J|7|S|8|@]|9|@]|A|$K|L]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

This is a performance enhancement on top of the accepted solution. Iterating though all classes can be slow because there are so many. Sometimes you can filter out an entire assembly without looking at any of its types. 

For example if you are looking for an attribute that you declared yourself, you don't expect any of the system DLLs to contain any types with that attribute. The Assembly.GlobalAssemblyCache property is a quick way to check for system DLLs. When I tried this on a real program I found I could skip 30,101 types and I only have to check 1,983 types.

Another way to filter is to use Assembly.ReferencedAssemblies. Presumably if you want classes with a specific attribute, and that attribute is defined in a specific assembly, then you only care about that assembly and other assemblies that reference it. In my tests this helped slightly more than checking the GlobalAssemblyCache property.

I combined both of these and got it even faster. The code below includes both filters.

<pre><code> string definedIn = typeof(XmlDecoderAttribute).Assembly.GetName().Name;
 foreach (Assembly assembly in AppDomain.CurrentDomain.GetAssemblies())
 // Note that we have to call GetName().Name. Just GetName() will not work. The following
 // if statement never ran when I tried to compare the results of GetName().
 if ((!assembly.GlobalAssemblyCache) &amp;&amp; ((assembly.GetName().Name == definedIn) || assembly.GetReferencedAssemblies().Any(a =&gt; a.Name == definedIn)))
 foreach (Type type in assembly.GetTypes())
 if (type.GetCustomAttributes(typeof(XmlDecoderAttribute), true).Length &gt; 0)
</code></pre>

blocks|key|1613117|text|我们可以改进Andrew的回答，并将整个问题转换为一个LINQ查询。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1613118|++++public+static+IEnumerable<Type>+GetTypesWithHelpAttribute(Assembly+assembly)
++++{
++++++++return+assembly.GetTypes().Where(type+=>+type.GetCustomAttributes(typeof(HelpAttribute),+true).Length+>+0);
++++}|code-block|syntax|javascript|1613119|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|$]]

We can improve on Andrew's answer and convert the whole thing into one LINQ query.

<pre><code> public static IEnumerable&lt;Type&gt; GetTypesWithHelpAttribute(Assembly assembly)
 {
 return assembly.GetTypes().Where(type =&gt; type.GetCustomAttributes(typeof(HelpAttribute), true).Length &gt; 0);
 }
</code></pre>

blocks|key|1613220|text|这是Trade-Ideas+philip提供的代码的另一个版本，我已经将代码压缩到linq中，并将其插入到一个很好的静态函数中，您可以将其放入项目中。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1613221|原创：https://stackoverflow.com/a/41411243/4122889|offset|length|1613222|我还添加了AsParallel()+-在我的机器上有足够的内核等，并且有一个‘正常’规模的项目(这完全是主观的)，这是最快的/|style|CODE|1613223|在没有AsParallel()的情况下，大约200个结果需要1.5秒，有了它，大约需要几毫秒-因此在我看来这似乎是最快的。|1613224|请注意，这将跳过GAC中的程序集。|1613225|private+static+IEnumerable<IEnumerable<T>>+GetAllAttributesInAppDomain<T>()
{
++++var+definedIn+=+typeof(T).Assembly.GetName().Name;
++++var+assemblies+=+AppDomain.CurrentDomain.GetAssemblies();

+++var+res+=+assemblies.AsParallel()
++++++++.Where(assembly+=>+(!assembly.GlobalAssemblyCache)+&&+((assembly.GetName().Name+==+definedIn)+%7C%7C
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++assembly.GetReferencedAssemblies()
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++.Any(a+=>+a.Name+==+definedIn))
++++++++++++)
++++++++.SelectMany(c+=>+c.GetTypes())
++++++++.Select(type+=>+type.GetCustomAttributes(typeof(T),+true)
++++++++++++.Cast<T>()
++++++++++++)
++++++++.Where(c+=>+c.Any());

++++return+res;
}|code-block|syntax|javascript|1613226|用法：|1613227|var+allAttributesInAppDomain+=+GetAllAttributesInAppDomain<ExportViewAttribute>();|1613228|注意:如果每个类只有一个属性，而不是多个属性，那么将结果从IEnumerable<IEnumerable<T>>转换为IEnumerable<T>会更容易，如下所示：|1613229|var+allAttributesInAppDomainFlattened+=+allAttributesInAppDomain.SelectMany(c+=>+c);|1613230|记住，这使用了IEnumerable，所以调用ToList()来实际运行函数。|1613231|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/a/41411243/4122889^0|0|3|18|0|0|5|C|0|3|C|0|0|0|0|0|T|R|1N|E|0|0|7|B|N|8|0^^$0|@$1|2|3|4|5|6|7|1A|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|1B|8|@]|9|@$D|1C|E|1D|1|1E]]|A|$]]|$1|F|3|G|5|6|7|1F|8|@$D|1G|E|1H|H|I]]|9|@]|A|$]]|$1|J|3|K|5|6|7|1I|8|@$D|1J|E|1K|H|I]]|9|@]|A|$]]|$1|L|3|M|5|6|7|1L|8|@]|9|@]|A|$]]|$1|N|3|O|5|P|7|1M|8|@]|9|@]|A|$Q|R]]|$1|S|3|T|5|6|7|1N|8|@]|9|@]|A|$]]|$1|U|3|V|5|P|7|1O|8|@]|9|@]|A|$Q|R]]|$1|W|3|X|5|6|7|1P|8|@$D|1Q|E|1R|H|I]|$D|1S|E|1T|H|I]]|9|@]|A|$]]|$1|Y|3|Z|5|P|7|1U|8|@]|9|@]|A|$Q|R]]|$1|10|3|11|5|6|7|1V|8|@$D|1W|E|1X|H|I]|$D|1Y|E|1Z|H|I]]|9|@]|A|$]]|$1|12|3|-4|5|6|7|20|8|@]|9|@]|A|$]]]|13|$14|$5|15|16|17|A|$18|19]]]]

This is another version of the code provided by Trade-Ideas philip,
I've condensed the code to linq, plugged it into a nice static function which you can just drop in the project.
Original:
<a href="https://stackoverflow.com/a/41411243/4122889">https://stackoverflow.com/a/41411243/4122889</a>
I've also added <code>AsParallel()</code> - on my machine with enough cores etc, and with a 'normally' sized project (which is completely subjective), this was the fastest/
Without <code>AsParallel()</code> this took 1,5 seconds for about 200 results, and with it, it took about a couple milliseconds - therefore this seems the fastest to me.
Note that this skips the assemblies in the GAC.
<pre class="lang-cs prettyprint-override"><code>private static IEnumerable&lt;IEnumerable&lt;T&gt;&gt; GetAllAttributesInAppDomain&lt;T&gt;()
{
 var definedIn = typeof(T).Assembly.GetName().Name;
 var assemblies = AppDomain.CurrentDomain.GetAssemblies();

 var res = assemblies.AsParallel()
 .Where(assembly =&gt; (!assembly.GlobalAssemblyCache) &amp;&amp; ((assembly.GetName().Name == definedIn) ||
 assembly.GetReferencedAssemblies()
 .Any(a =&gt; a.Name == definedIn))
 )
 .SelectMany(c =&gt; c.GetTypes())
 .Select(type =&gt; type.GetCustomAttributes(typeof(T), true)
 .Cast&lt;T&gt;()
 )
 .Where(c =&gt; c.Any());

 return res;
}

</code></pre>
Usage:
<pre class="lang-cs prettyprint-override"><code>var allAttributesInAppDomain = GetAllAttributesInAppDomain&lt;ExportViewAttribute&gt;();
</code></pre>
Note if you have only 1 attribute per class, so not multiple, its easier to flatten the result from <code>IEnumerable&lt;IEnumerable&lt;T&gt;&gt;</code> to <code>IEnumerable&lt;T&gt;</code> like so:
<pre class="lang-cs prettyprint-override"><code>var allAttributesInAppDomainFlattened = allAttributesInAppDomain.SelectMany(c =&gt; c);
</code></pre>
Remember, this uses <code>IEnumerable</code> so call <code>ToList()</code> to actually run the function.

Question based on <a href="https://web.archive.org/web/20170228051218/https://msdn.microsoft.com/en-us/library/aa288454(VS.71).aspx" rel="noreferrer">MSDN example</a>.

Let's say we have some C# classes with HelpAttribute in standalone desktop application. Is it possible to enumerate all classes with such attribute? Does it make sense to recognize classes this way? Custom attribute would be used to list possible menu options, selecting item will bring to screen instance of such class. Number of classes/items will grow slowly, but this way we can avoid enumerating them all elsewhere, I think.

How enumerate all classes with custom class attribute?

基于的问题。假设我们在独立的桌面应用程序中有一些带有HelpAttribute的C#类。是否可以枚举具有此类属性的所有类？以这种方式识别类有意义吗？自定义属性将用于列出可能的菜单选项，选择项将显示此类类的屏幕实例。类/项的数量将缓慢增长，但我认为这样我们就可以避免在其他地方枚举它们。

问如何枚举所有具有自定义类属性的类？
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