How to: Expose Code to VBA in a Visual C# Project

Article
04/28/2015

You can expose code in a Visual C# project to Visual Basic for Applications (VBA) code if you want the two types of code to interact with each other.

The Visual C# process is different from the Visual Basic process. For more information, see How to: Expose Code to VBA in a Visual Basic Project.

Applies to: The information in this topic applies to document-level projects for the following applications: Excel 2013 and Excel 2010; Word 2013 and Word 2010. For more information, see Features Available by Office Application and Project Type.

Exposing Code in a Visual C# Project

To enable VBA code to call code in a Visual C# project, modify the code so it is visible to COM, and then set the ReferenceAssemblyFromVbaProject property to True in the designer.

For a walkthrough that demonstrates how to call a method in a Visual C# project from VBA, see Walkthrough: Calling Code from VBA in a Visual C# Project.

To expose code in a Visual C# project to VBA

Open or create a document-level project that is based on a Word document, Excel workbook, or Excel template that supports macros, and that already contains VBA code.

For more information about the document file formats that support macros, see Combining VBA and Document-Level Customizations.

Note

This feature cannot be used in Word template projects.
Ensure that VBA code in the document is allowed to run without prompting the user to enable macros. You can trust VBA code to run by adding the location of the Office project to the list of trusted locations in the Trust Center settings for Word or Excel.
Add the member that you want to expose to VBA to a public class in your project, and declare the new member as public.
Apply the following ComVisibleAttribute and ClassInterfaceAttribute attributes to the class that you are exposing to VBA. These attributes make the class visible to COM, but without generating a class interface.
```
[System.Runtime.InteropServices.ComVisible(true)]
[System.Runtime.InteropServices.ClassInterface(
    System.Runtime.InteropServices.ClassInterfaceType.None)]
```
Override the GetAutomationObject method of a host item class in your project to return an instance of the class that you are exposing to VBA:
- If you are exposing a host item class to VBA, override the GetAutomationObject method that belongs to this class, and return the current instance of the class.
```
protected override object GetAutomationObject()
{
    return this;
}
```
- If you are exposing a class that is not a host item to VBA, override the GetAutomationObject method of any host item in your project, and return an instance of the non-host item class. For example, the following code assumes that you are exposing a class named DocumentUtilities to VBA.
```
protected override object GetAutomationObject()
{
    return new DocumentUtilities();
}
```
For more information about host items, see Host Items and Host Controls Overview.
Extract an interface from the class that you are exposing to VBA. In the Extract Interface dialog box, select the public members that you want to include in the interface declaration. For more information, see Extract Interface Refactoring (C#).
Add the public keyword to the interface declaration.
Make the interface visible to COM by adding the following ComVisibleAttribute attribute to the interface.
```
[System.Runtime.InteropServices.ComVisible(true)]
```
Open the document (for Word) or worksheet (for Excel) in the designer in Visual Studio.
In the Properties window, select the ReferenceAssemblyFromVbaProject property, and change the value to True.

Note

If the workbook or document does not already contain VBA code or if VBA code in the document is not trusted to run, you will receive an error message when you set the ReferenceAssemblyFromVbaProject property to True. This is because Visual Studio cannot modify the VBA project in the document in this situation.
Click OK in the message that is displayed. This message reminds you that if you add VBA code to the workbook or document when running the project from Visual Studio, the VBA code will be lost the next time that you build the project. This is because the document in the build output folder is overwritten every time that you build the project.

At this point, Visual Studio configures the project so that the VBA project can call into the assembly. Visual Studio also adds a method named GetManagedClass to the VBA project. You can call this method from anywhere in the VBA project to access the class that you exposed to VBA.
Build the project.

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How to: Expose Code to VBA in a Visual C# Project

Exposing Code in a Visual C# Project

To expose code in a Visual C# project to VBA

See Also

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