Lot of people trying to edit the code when ASP.NET Development Server is running but they can't. In order to edit code you have to stop debugger/ ASP.NET Development server then you can edit it.
If you want to continue code edit while your are running ASP.NET Development Server try this:
You do have the option to control which port is used when using the
built-in development server. The steps to specify the port to be used
are slightly different depending on whether you are using a website
project or a web application project.ASP.NET Development Server - Web Application project
Right click the Project in the Solution Explorer, and then select “Properties”
Click “Web” tab.
Go to Server section (Make sure Visual Studio Development server is selected)
- Check Enable Edit and Continue is turned on