Re: What types should I use in this COM Interface

Oolis Kraprin wrote:
Hi, I am having to write a COM wrapper dll to enable the use of a c++
library in a c# .net app, and have a few questions regarding what
types to use in the interface.

I used to program quite a bit of COM, but a couple of years of c# .net
has made me stupid.

Anyway, I need to pass (from c# to the com component) a HWND window
handle, and 2 strings. The function needs to deliver back to c# 2
lists or arrays of strings.

My guess at the moment is something like:
ULONG WindowHandle

There are plenty of ways to marshal an HWND, but the easiest and still bit-safe way is to use a HANDLE as the native type (and cast between HWND and HANDLE on the C++ end).

BSTR FirstString
BSTR SecondString
VARIANT* FirstReturnedStringArray or List
VARIANT* SecondReturnedStringArray or List

and I probably need to return 2 ints indicating the length of the 2
lists right, or is there some type for representing a list of array of
strings that contains the count?

SAFEARRAY. The IDL could look like this:

[uuid(...)]
library Test {
[object, uuid(...)]
interface ITest : IUnknown {
HRESULT Foo([in] HANDLE hwnd, [in] BSTR firstString, [in] BSTR secondString, [out] SAFEARRAY(BSTR)* firstArray, [out] SAFEARRAY(BSTR)* secondArray);
}
}

Put this in a type library and let tlbimp.exe do its magic, and it should produce something that looks a lot like this without the need for any marshalling:

void Foo(IntPtr hwnd, string firstString, string secondString, out string[] firstArray, out string[] secondArray);

Using SAFEARRAYs in C++ is a bit of a chore, but the ATL helper clas CComSafeArray goes a long way towards easing the pain.

--
J.
.

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