single app.config multi-project c#

Let’s say you have this folder structure:

• Solution
  • Project1
  • Project2
  • Project3

Do this:

1. Create the App.config file in the Solution level folder. You won’t find an option to add an App.config file from the templates, so just create a new empty text file with the name App.config, and paste in the contents of a regular App.config file.

2. For each project in Solution Explorer:

   1. Right click and select Add > Existing Item
   2. Locate the file

   3. Select Add as link from the drop down box next to the Add button.

      

Edited to add:

You correctly state that the above method only shared the file up to build-time. To use a shared file at run-time, see the answers to this question.