How to launch an app with double-click on filename

[Dick Swager]

I have an Windows Form application that has child Forms in it. I have a
constructor in the main form that takes a filename as an argument an creates
a child form from the data in the file. If I launch the app from the
command prompt with a filename as an argument, it works fine. But if I
launch the application by double-clicking on the filename in Windows
Explorer the child form is not created.

I thought that double-clicking a filename was the same as using the command
prompt with the file name as an argument at the point where the application
is launched, but apparently this is not true. Do I have to handle the two
situations differently in my code? Or do I do something at the OS level
that will make this work as I thought it should?

TIA, Dick