Hi,
I have created this drop list that will display all files within a folder. It will look for files in 'C:\Mach4Hobby\MDI Files'. You can then select the file from the drop down and it will load it into the MDI window and you can run it as normal. I've also added a save button so you can easily create and save new files.
All the code is self contained within the MDI tab. I have exported it so you can easily import it without having to copy and paste code. First extract the attached .zip file. To import, go into the screen editor, right click 'nbGCodeMDI' and click import. Then select the .setc file you just extracted. Make sure the controls are named as in the picture otherwise it will not work. It may be best to delete your current MDI tab before importing. Also make a backup of your screen file before doing anything just in case!