blocks|key|2630033|text|如果公共类型在默认情况下是可见的，那么将ComVisible属性设置为true+ComVisible(true)是如何使公共类型可见的，这是没有意义的。|type|blockquote|depth|inlineStyleRanges|entityRanges|data|2630034|默认情况下，它们是可见的，因为ComVisibleAttribute的默认值为true。将属性显式设置为true不会改变任何事情，它只会使您的意图更加明确。这是您找到的文献资料的第一行：|unstyled|offset|length|2630035|缺省值是true，它指示托管类型对COM是可见的。要使公共托管程序集和类型可见，不需要此属性；默认情况下，它们对COM是可见的。只能使公共类型可见。该属性不能用于使其他内部或受保护的类型对COM可见，也不能用于使不可见类型的成员可见。|style|BOLD|2630036|基本上，如果你不自己去做的话，你可以把它想象成编译器总是默认地将[ComVisibleAttribute(true)]添加到你的代码中。|CODE|2630037|您需要设置此属性的唯一原因是防止公共类型是COM可见的(在这种情况下，您将其设置为false)。默认值已经确保了它们的可见性。|2630038|显然，非公共类型(例如，私有类型和受保护类型)不能也永远不会在COM中可见。此属性对具有此类可访问性的类型没有任何影响。|2630039|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-us/library/system.runtime.interopservices.comvisibleattribute.aspx^0|0|2C|4|0|0|4|4|1V|2|0|W|R|0|0|0^^$0|@$1|2|3|4|5|6|7|Z|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|10|8|@]|9|@$E|11|F|12|1|13]]|A|$]]|$1|G|3|H|5|6|7|14|8|@$E|15|F|16|I|J]|$E|17|F|18|I|J]]|9|@]|A|$]]|$1|K|3|L|5|D|7|19|8|@$E|1A|F|1B|I|M]]|9|@]|A|$]]|$1|N|3|O|5|D|7|1C|8|@]|9|@]|A|$]]|$1|P|3|Q|5|D|7|1D|8|@]|9|@]|A|$]]|$1|R|3|-4|5|D|7|1E|8|@]|9|@]|A|$]]]|S|$T|$5|U|V|W|A|$X|Y]]]]

<blockquote>
 It does not makes sense, when public types are visible by default, so how does setting ComVisible attribute to true [ComVisible(true)] makes public types visible.
</blockquote>

They're visible by default because the default value of the ComVisibleAttribute is true. Setting the attribute explicitly to true doesn't change anything, it just makes your intentions more clear. That's the very first line of <a href="http://msdn.microsoft.com/en-us/library/system.runtime.interopservices.comvisibleattribute.aspx" rel="noreferrer">the documentation</a> you found:

<blockquote>
 The default is true, which indicates that the managed type is visible to COM. This attribute is not needed to make public managed assemblies and types visible; they are visible to COM by default. Only public types can be made visible. The attribute cannot be used to make an otherwise internal or protected type visible to COM or to make members of a nonvisible type visible.
</blockquote>

Basically, you can think of it like the compiler always adds <code>[ComVisibleAttribute(true)]</code> to your code by default if you don't do it yourself.

The only reason you would need to set this attribute is to prevent public types from being COM-visible (in which case you would set it to false). The default already ensures their visibility.

Obviously, non-public types (e.g., private and protected) cannot and will not ever be visible to COM. This attribute has no effect on types with such accessibility.

blocks|key|520302|text|诀窍是您还可以在程序集级别(在AssemblyInfo.cs中)添加此属性。如果您指定了[assembly:+ComVisible(true)]+(或者没有在程序集级别指定它，在默认情况下具有相同的效果)，那么所有公共类和接口及其公共方法在默认情况下都是可见的。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|520303|您也可以在程序集级别设置[assembly:+ComVisible(false)]，然后所有公共实体在默认情况下都会产生相同的效果，就像它们上面有[ComVisible(false)]一样，因此您只能标记真正需要的类/接口/方法COM-可见([ComVisible(true)])。|520304|这可以帮助您在有大量公共实体(如这里+)时不公开太多。如果没有这种机制，就必须将[ComVisible(false)]设置为每个不希望公开的类/接口/方法。使用[assembly:+ComVisible(false)]可以使您只公开所需的内容。|520305|而且您只能将public实体公开给COM+(默认的或显式的)--更严格的可见性的实体不能暴露给COM。|520306|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/q/1649752/57428^0|18|S|0|C|T|21|J|3D|I|0|14|J|28|T|G|2|0|0|6|6|0^^$0|@$1|2|3|4|5|6|7|T|8|@$9|U|A|V|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|W|8|@$9|X|A|Y|B|C]|$9|Z|A|10|B|C]|$9|11|A|12|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|13|8|@$9|14|A|15|B|C]|$9|16|A|17|B|C]]|D|@$9|18|A|19|1|1A]]|E|$]]|$1|J|3|K|5|6|7|1B|8|@$9|1C|A|1D|B|C]]|D|@]|E|$]]|$1|L|3|-4|5|6|7|1E|8|@]|D|@]|E|$]]]|M|$N|$5|O|P|Q|E|$R|S]]]]

The trick is you can also add this attribute at assembly level (in AssemblyInfo.cs). If you specify <code>[assembly: ComVisible(true)]</code> (or don't specify that at assembly level and so have the same effect by default) then all the public classes and interfaces and public methods thereof become COM-visible by default.

You could just as well set <code>[assembly: ComVisible(false)]</code> at assembly level and then all the public entities would by default have the same effect as if they had <code>[ComVisible(false)]</code> on them and so you could only mark those classes/interfaces/methods COM-visible (<code>[ComVisible(true)]</code>) which you really need.

This helps you to not expose too much when you have lots of public entities as <a href="https://stackoverflow.com/q/1649752/57428">here</a>. Without this mechanism you would have to set <code>[ComVisible(false)]</code> to each class/interface/method that you don't want exposed. Using <code>[assembly: ComVisible(false)]</code> lets you only expose the stuff you need.

And you only can expose <code>public</code> entities to COM (be default or explicitly) - entities with stricter visibility can't be exposed to COM.

MSDN has <a href="http://msdn.microsoft.com/en-us/library/system.runtime.interopservices.comvisibleattribute.aspx" rel="noreferrer">this article about <code>[ComVisible]</code> attribute</a>. I don't quite get what happens when one sets <code>[ComVisible(true)]</code>.

MSDN says

<blockquote>
 The default is true, which indicates that the managed type is visible to COM. This attribute is not needed to make public managed assemblies and types visible; they are visible to COM by default. Only public types can be made visible.
</blockquote>

So they say public types are visible to COM by default. But they also say only public types can be made visible by setting <code>[ComVisible(true)]</code>. It does not makes sense: if public types are visible by default, then how does setting <code>[ComVisible(true)]</code> make public types visible? If they're already visible how will they get more visible?

Perhaps my understanding is not correct. I shall appreciate if anyone can put some light on the above statements.

What's the deal with [ComVisible] default and public classes COM exposure?

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。

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MSDN有。当设置[ComVisible(true)]时，我不太明白会发生什么。MSDN说默认值为真，这表明托管类型对COM是可见的。为了使公共托管程序集、和类型成为可见的，不需要此属性；它们在默认情况下对COM是可见的。只能显示公共类型。所以他们说，默认情况下，公共类型对COM是可见的。但他们也表示，只有公共类型可以...

问[ComVisible]默认和公共类COM公开有什么关系？
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问[ComVisible]默认和公共类COM公开有什么关系？EN