blocks|key|1528476|text|不，不是的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1528477|属性是元数据，以二进制形式存储在编译后的程序集中(这也是为什么您只能在其中使用简单类型的原因)。|1528478|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

No, it's not.

Attributes are meta-data and stored in binary-form in the compiled assembly (that's also why you can only use simple types in them).

blocks|key|1528508|text|一种解决办法可能是在运行时生成一个派生类并添加属性，尽管这可能有点夸张。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1528509|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

You can't. One workaround might be to generate a derived class at runtime and adding the attribute, although this is probably bit of an overkill.

blocks|key|1743595|text|属性是静态元数据。程序集、模块、类型、成员、参数和返回值在C#中不是一级对象(例如，System.Type类仅仅是一个类型的反射表示)。您可以获取一个类型的属性实例，并更改属性(如果它们是可写的)，但这不会影响应用于该类型的属性。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1743596|entityMap^0|16|B|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|K|8|@]|D|@]|E|$]]]|G|$]]

Attributes are static metadata. Assemblies, modules, types, members, parameters, and return values aren't first-class objects in C# (e.g., the <code>System.Type</code> class is merely a reflected representation of a type). You can get an instance of an attribute for a type and change the properties if they're writable but that won't affect the attribute as it is applied to the type.

blocks|key|1743647|text|如果您需要能够动态添加的内容，则c#属性不是合适的方法。研究一下在xml中存储数据。我最近做了一个项目，我从w/+attributes开始，但最终转向了w/+xml序列化。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1743648|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

If you need something to be able to added dynamically, c# attributes aren't the way. Look into storing the data in xml. I recently did a project that i started w/ attributes, but eventually moved to serialization w/ xml.

blocks|key|1743672|text|为什么你需要这样做？属性为反射提供了额外的信息，但如果您在外部知道需要哪些属性，则不需要它们。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1743673|您可以在外部相对容易地将元数据存储在数据库或资源文件中。|1743674|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

Why do you need to? Attributes give extra information for reflection, but if you externally know which properties you want you don't need them.

You could store meta data externally relatively easily in a database or resource file.

blocks|key|1528732|text|这真的取决于你到底想要实现什么。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1528733|System.ComponentModel.TypeDescriptor可以用来向类型、属性和对象实例添加属性，但它也有一个限制，即您必须使用它来检索这些属性。如果您正在编写使用这些属性的代码，并且您可以在这些限制中生存，那么我绝对建议您这样做。|offset|length|1528734|据我所知，PropertyGrid控件和visual+studio设计图面是BCL中唯一使用TypeDescriptor的东西。事实上，这就是他们如何做他们真正需要做的事情的一半。|1528735|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-us/library/system.componentmodel.typedescriptor.aspx^0|0|0|10|0|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Q|8|@]|9|@$D|R|E|S|1|T]]|A|$]]|$1|F|3|G|5|6|7|U|8|@]|9|@]|A|$]]|$1|H|3|-4|5|6|7|V|8|@]|9|@]|A|$]]]|I|$J|$5|K|L|M|A|$N|O]]]]

This really depends on what exactly you're trying to accomplish.

The <a href="http://msdn.microsoft.com/en-us/library/system.componentmodel.typedescriptor.aspx" rel="noreferrer">System.ComponentModel.TypeDescriptor</a> stuff can be used to add attributes to types, properties and object instances, and it has the limitation that you have to use it to retrieve those properties as well. If you're writing the code that consumes those attributes, and you can live within those limitations, then I'd definitely suggest it.

As far as I know, the PropertyGrid control and the visual studio design surface are the only things in the BCL that consume the TypeDescriptor stuff. In fact, that's how they do about half the things they really need to do.

blocks|key|1528808|text|好吧，为了不同，我找到了一篇文章，其中提到了使用Reflection.Emit来做这件事。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1528809|这里是链接：http://www.codeproject.com/KB/cs/dotnetattributes.aspx，您还需要查看文章底部的一些注释，因为这里讨论了可能的方法。|offset|length|1528810|entityMap|0|LINK|mutability|MUTABLE|url|http://www.codeproject.com/KB/cs/dotnetattributes.aspx^0|0|6|1I|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|O|8|@]|9|@$D|P|E|Q|1|R]]|A|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|A|$]]]|G|$H|$5|I|J|K|A|$L|M]]]]

Well, just to be different, I found an article that references using Reflection.Emit to do so. 

Here's the link: <a href="http://www.codeproject.com/KB/cs/dotnetattributes.aspx" rel="noreferrer">http://www.codeproject.com/KB/cs/dotnetattributes.aspx</a> , you will also want to look into some of the comments at the bottom of the article, because possible approaches are discussed.

blocks|key|1743853|text|在Java中，我过去常常通过使用map和实现我自己的键值编码来解决这个问题。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1743854|http://developer.apple.com/documentation/Cocoa/Conceptual/KeyValueCoding/KeyValueCoding.html|offset|length|1743855|entityMap|0|LINK|mutability|MUTABLE|url^0|0|0|2K|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@$D|O|E|P|1|Q]]|A|$]]|$1|F|3|-4|5|6|7|R|8|@]|9|@]|A|$]]]|G|$H|$5|I|J|K|A|$L|C]]]]

In Java I used to work around this by using a map and implementing my own take on Key-Value coding.

<a href="http://developer.apple.com/documentation/Cocoa/Conceptual/KeyValueCoding/KeyValueCoding.html" rel="nofollow noreferrer">http://developer.apple.com/documentation/Cocoa/Conceptual/KeyValueCoding/KeyValueCoding.html</a>

blocks|key|1743922|text|就像Deczaloth在下面的评论中提到的那样，我认为元数据在编译时是固定的。我通过创建一个动态对象来实现它，其中我覆盖了GetType()或使用GetCustomType()并编写了我自己的类型。用这个你就可以..。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1743923|我非常努力地尝试了System.ComponentModel.TypeDescriptor，但没有成功。这并不意味着它不能工作，但我希望看到它的代码。|1743924|另一方面，我想更改一些属性值。我做了两个函数，这两个函数可以很好地实现这个目的。|1743925|++++++++//+************************************************************************
++++++++public+static+void+SetObjectPropertyDescription(this+Type+typeOfObject,+string+propertyName,++string+description)
++++++++{
++++++++++++PropertyDescriptor+pd+=+TypeDescriptor.GetProperties(typeOfObject)[propertyName];
++++++++++++var+att+=+pd.Attributes[typeof(DescriptionAttribute)]+as+DescriptionAttribute;
++++++++++++if+(att+!=+null)
++++++++++++{
++++++++++++++++var+fieldDescription+=+att.GetType().GetField("description",+BindingFlags.NonPublic+%7C+BindingFlags.Instance);
++++++++++++++++if+(fieldDescription+!=+null)
++++++++++++++++{
++++++++++++++++++++fieldDescription.SetValue(att,+description);
++++++++++++++++}
++++++++++++}
++++++++}

++++++++//+************************************************************************
++++++++public+static+void+SetPropertyAttributReadOnly(this+Type+typeOfObject,+string+propertyName,+bool+isReadOnly)
++++++++{
++++++++++++PropertyDescriptor+pd+=+TypeDescriptor.GetProperties(typeOfObject)[propertyName];
++++++++++++var+att+=+pd.Attributes[typeof(ReadOnlyAttribute)]+as+ReadOnlyAttribute;
++++++++++++if+(att+!=+null)
++++++++++++{
++++++++++++++++var+fieldDescription+=+att.GetType().GetField("isReadOnly",+BindingFlags.NonPublic+%7C+BindingFlags.Instance);
++++++++++++++++if+(fieldDescription+!=+null)
++++++++++++++++{
++++++++++++++++++++fieldDescription.SetValue(att,+isReadOnly);
++++++++++++++++}
++++++++++++}
++++++++}|code-block|syntax|javascript|1743926|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|O|8|@]|9|@]|A|$]]|$1|F|3|G|5|H|7|P|8|@]|9|@]|A|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Like mentionned in a comment below by Deczaloth, I think that metadata is fixed at compile time. I achieve it by creating a dynamic object where I override GetType() or use GetCustomType() and writing my own type. Using this then you could...
I tried very hard with System.ComponentModel.TypeDescriptor without success. That does not means it can't work but I would like to see code for that.
In counter part, I wanted to change some Attribute values.
I did 2 functions which work fine for that purpose.
<pre><code> // ************************************************************************
 public static void SetObjectPropertyDescription(this Type typeOfObject, string propertyName, string description)
 {
 PropertyDescriptor pd = TypeDescriptor.GetProperties(typeOfObject)[propertyName];
 var att = pd.Attributes[typeof(DescriptionAttribute)] as DescriptionAttribute;
 if (att != null)
 {
 var fieldDescription = att.GetType().GetField(&quot;description&quot;, BindingFlags.NonPublic | BindingFlags.Instance);
 if (fieldDescription != null)
 {
 fieldDescription.SetValue(att, description);
 }
 }
 }

 // ************************************************************************
 public static void SetPropertyAttributReadOnly(this Type typeOfObject, string propertyName, bool isReadOnly)
 {
 PropertyDescriptor pd = TypeDescriptor.GetProperties(typeOfObject)[propertyName];
 var att = pd.Attributes[typeof(ReadOnlyAttribute)] as ReadOnlyAttribute;
 if (att != null)
 {
 var fieldDescription = att.GetType().GetField(&quot;isReadOnly&quot;, BindingFlags.NonPublic | BindingFlags.Instance);
 if (fieldDescription != null)
 {
 fieldDescription.SetValue(att, isReadOnly);
 }
 }
 }
</code></pre>

Is it possible to add attributes at runtime or to change the value of an attribute at runtime?

问是否可以在C#中动态添加属性？
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