Use CLR classes from COM addin in Excel VBA?

问题

I have an Excel VSTO COM addin, which I can successfully load an refer to in Excel VBA. I can exchange basic types (like strings), but can I also use complex classes from my addin in VBA?

Let's say I have this class in C#:

public class TestClass {
    public string GetTextFunc() => "check";
    public string TextProp => "doublecheck";
    public int RollDice() => 4; // chosen by fair dice roll
}

...and my addin provides an object of this class to Excel:

[ComVisible(true)]
public interface IUtilities {
    string GetString();
    TestClass GetTestClass();
}

[ComVisible(true)]
[ClassInterface(ClassInterfaceType.None)]
public class Utilities: IUtilities {
    public string GetString() => "Hello Excel";
    public TestClass GetTestClass() => new TestClass();
}

So everything is pretty default VSTO-tutorial-stuff, except for that class.

Now when I use my addin in the Excel VBA block (e.g. in "ThisWorksheet"), by defining a function like such:

Sub TestAddin()
    Dim addIn As COMAddIn
    Dim automationObject As Object
    Set addIn = Application.COMAddIns("MyExcelAddin")
    Set automationObject = addIn.Object
    
    ActiveSheet.Range("A1").Value2 = automationObject.GetString()
    
    Dim tc
    Set tc = automationObject.GetTestClass()
    ActiveSheet.Range("A2").Value2 = tc.GetTextFunc()
End Sub

...then A1 is correctly set, as expected, and I can debug-step all the way to the last line (so getting the object of tc still works!), but on the last line I get an error "Object required". I can see that tc is of type Variant/Object, so I assume VBA just doesn't know what to do with it. Is there any way to

Tell VBA how this class looks like and
actually have it work, so that calling a function on tc in VBA calls the correct code in my .Net library?

回答1:

TestClass class must be implemented just like your Utilities class - it must implement a public IDispatch-derived interface.

[ComVisible(true)]
public interface ITestClass {
    string GetTextFunc();
    string TextProp ();
    int RollDice();
}

[ComVisible(true)]
[ClassInterface(ClassInterfaceType.None)]
public class TestClass : ITestClass {
    public string GetTextFunc() => "check";
    public string TextProp => "doublecheck";
    public int RollDice() => 4;
}

Now the VBA call has a Class Interface to the methods such as GetTextFunc:

Dim tc
Set tc = automationObject.GetTestClass()
ActiveSheet.Range("A2").Value2 = tc.GetTextFunc()

来源：https://stackoverflow.com/questions/62916800/use-clr-classes-from-com-addin-in-excel-vba

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