C# and VBA interop - C# Discussion Boards

3-Sep-12 3:10

Hello everyone,

I need to write a method in C# that can be called from VBA using COM. The primitive types can be directly passed to the method and returned from it, but what about the complex types? For instance, the C# List<> will have to be converted in a VB Collection.

Thanks, in advance,
Mark

Eddy Vluggen3-Sep-12 3:28

Eddy Vluggen

3-Sep-12 3:28

mark4 wrote:
The primitive types can be directly passed to the method and returned from it, but what about the complex types? For instance, the C# List<> will have to be converted in a VB Collection.

Have you considered switching from VBA to PowerShell? That way you'd be able to use the complex types from the script.

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mark46-Sep-12 5:09

6-Sep-12 5:09

I can't, I have to use C#.

Eddy Vluggen6-Sep-12 5:14

Eddy Vluggen

6-Sep-12 5:14

To replace the VBA part, not the C#-part; it's got a bit better support for .NET.

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mark46-Sep-12 5:25

6-Sep-12 5:25

I can't either. lol I'm struggling to find a simple tutorial on how to make a COM class to exchange bewteen applications. I'm not familiar at all with COM.

Dave Kreskowiak3-Sep-12 4:00

Dave Kreskowiak

3-Sep-12 4:00

If I remember correctly, the List and List<t> types are not COM-visible. You cannot use them from VBScript and use them as return values to VBScript. You would have to replace them with Array equivelents.

You would have to convert all of your comlex return values/types down to simpler types that VBScript is familiar with.

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Dave Kreskowiak

mark46-Sep-12 5:11

6-Sep-12 5:11

First, I'm not using VBScript but VBA. Second, it's not so easy, my C# method must return a binary tree. So it can't be represented with primitive types.

Dave Kreskowiak6-Sep-12 6:31

Dave Kreskowiak

6-Sep-12 6:31

mark4 wrote:
First, I'm not using VBScript but VBA

Does not matter. You have the same limitations.

mark4 wrote:
Second, it's not so easy, my C# method must return a binary tree.

OK, so you're going to have to represent your binary tree in a format that's more portable acrossed COM.

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Dave Kreskowiak

mark47-Sep-12 2:02

7-Sep-12 2:02

That's right, so my question is: how to do it? I've gone thru several tutorials but I find them very difficult and they are too specific to an example. Do I need to create an interface? How do I generate GUIDs? Well, I have many questions... If you know a good and simple tutorial, if would help me.

Dave Kreskowiak7-Sep-12 8:50

Dave Kreskowiak

7-Sep-12 8:50

I don't know of any "simple" tutorials on this.

One design I would look at is a class in C# that manages the view of the tree that your VBA code sees. Basically giving the VBA code methods it can use to nagivate the tree and return the values contained in a specific node in the tree. Returning the entire tree is just silly.

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Dave Kreskowiak

StringBuilder error!!

Jassim Rahma2-Sep-12 11:26

Jassim Rahma

2-Sep-12 11:26

Hi.

I am getting the following error:

Object reference not set to an instance of an object.

here is my code:

private StringBuilder data_changed = new StringBuilder();
.....
.....
if (full_name != txtFullName.Text) data_changed.Append(String.Format(" - name: {0} -> {1}", full_name, txtFullName.Text)).AppendLine();

DaveyM692-Sep-12 11:30

DaveyM69

2-Sep-12 11:30

Put a break point on your if statement and examine the data you're working with when it's hit.
My guess is full_name is probably null...

Dave

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PIEBALDconsult2-Sep-12 12:47

PIEBALDconsult

2-Sep-12 12:47

And try AppendFormat.

Abhinav S2-Sep-12 17:27

Abhinav S

2-Sep-12 17:27

This error occurs when you try and access a property of an object that is already null.
Debug and figure out which of the values is throwing this error.

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BobJanova3-Sep-12 1:32

BobJanova

3-Sep-12 1:32

This is probably the easiest of all .Net exceptions to debug. One of the things you're trying to reference is null. On that line you have only txtFullName and data_changed being dereferenced, so it must be one of those. Work out which one it is and either change the calling context or null-protect this code.