vba - Can I use / access the app.config from .net code, when called via COM

Question

I have an existing set of .net libraries that I wish to call from Excel VBA (that part is working fine). These libraries rely on settings in the app.config. I know I can enter these settings in a excel.exe.config file (placed in the same directory as the excel.exe), but this doesn't really seem like a very manageable solution to me, as I can see causing conflicts if more than one application wants to do this.

My question is simple: is there any way of COM exposed dlls referring to their respective config files?

Sample app.config:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <appSettings>
    <add key="test" value="Hello world!" />
  </appSettings>
</configuration>

Sample c#:

namespace ExcelVbaFacingCode
{
    public class SimpleAppSettingReader
    {
        public string GetValue(string key)
        {
            return ConfigurationManager.AppSettings[key];
        }
    }
}

Sample VBA:

Public Sub Test()
    Dim Test As New SimpleAppSettingReader
    Dim sampleValue As String
    sampleValue = Test.GetValue("test")
    MsgBox "Value: '" + sampleValue + "'", vbOKOnly
End Sub

Answer 1

Whenever ConfigurationManager.AppSettings is called, it automatically opens the configuration file of the executing assembly. In your case, Excel is the executing application, so you cannot open the config file of the .Net DLL.

This was done for a reason. A single DLL can be called from multiple types of application, each of which might have different requirements (and possibly different databases, for example). For this reason, the application specifies the settings, not the referenced assembly.

I think that what you already suggested is the best way to do this. I know it seems like you are copying your config file, and that it means that you have duplicates out there to worry about when code changes, but its the best thing to do.