C# COM client get TypeLoadException when call C++ COM server function.

[KD Park]

I have a question.
I'm developing C# COM client and C++ COM server.

I created a function that returns SafeArray with a custom structure declared in C++. When I call this function in C# COM client as below, a TypeLoadException occurs.

----------- .idl file (C++) ---------------
interface ICustomInterface : IDispatch
{
HRESULT GetSafeArray([out, retval]SAFEARRAY(CustomStruct)* pStructArray);
};

----------- C# client ---------------
try
{
ICustomInterface custom = new CustomInterface();

Array arr = custom.GetSafeArray(); // TypeLoadException
if (arr != null)
{
}
}
catch (TypeLoadException ex)
{
System.Diagnostics.Debug.WriteLine(ex.Message);
}


So I tried several ways to solve this problem, and I found out that Exception does not occur when I try to do the following.

----------- C# client ---------------
try
{
ICustomInterface custom = new CustomInterface();

CustomStruct customStruct = new CustomStruct(); // TypeLoadException is not occur with this line of code.

Array arr = custom.GetSafeArray(); // TypeLoadException
if (arr != null)
{
}
}
catch (TypeLoadException ex)
{
System.Diagnostics.Debug.WriteLine(ex.Message);
}

The only difference is that declared the custom structure before calling the interface.
I really want to know why this is happening.

Thanks in advance.

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