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MSDN has this article about [ComVisible] attribute. I don't quite get what happens when one sets [ComVisible(true)].
MSDN says
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.
So they say public types are visible to COM by default. But they also say only public types can be made visible by setting [ComVisible(true)]. It does not makes sense: if public types are visible by default, then how does setting [ComVisible(true)] 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.
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You set the ComVisible property to true, when you need to expose public methods and functions in your assembly to other applications not written in . NET, which can then use the functionality in your assembly using Microsoft's COM, a standardized interface that binds to components at runtime.
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.
Other public members in the class that are not declared in these interfaces will not be visible to COM, but they will be visible to other .NET objects. To expose properties and methods to COM, you must declare them on the class interface and mark them with a DispId attribute, and implement them in the class.
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. So they say public types are visible to COM by default.
The class must be public. Properties, methods, and events must be public. Properties and methods must be declared on the class interface. Events must be declared in the event interface. Other public members in the class that are not declared in these interfaces will not be visible to COM, but they will be visible to other .NET objects.
If you specify [assembly: ComVisible (true)] (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.
The trick is you can also add this attribute at assembly level (in AssemblyInfo.cs). If you specify [assembly: ComVisible(true)] (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 [assembly: ComVisible(false)] at assembly level and then all the public entities would by default have the same effect as if they had [ComVisible(false)] on them and so you could only mark those classes/interfaces/methods COM-visible ([ComVisible(true)]) which you really need.
This helps you to not expose too much when you have lots of public entities as here. Without this mechanism you would have to set [ComVisible(false)] to each class/interface/method that you don't want exposed. Using [assembly: ComVisible(false)] lets you only expose the stuff you need.
And you only can expose public entities to COM (be default or explicitly) - entities with stricter visibility can't be exposed to COM.
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