Getting event when file is dragged to input field

I have a GUI that has two input fields.  The first one uses a  button that users can hit to browse to a file, and that file and path get plugged into the first field.

When the Browse button is used my second input field does some _PathSplit magic to grab just the file name from that selected file, so the result would look something like:

First GUICtrlCreateInput:
[C:\FilePath\SelectedFileName.exe]    [Browse for file button]

Second GUICtrlCreateInput:
[SelectedFileName]

This whole setup works really well, but my first input field also has the option for a file to be dragged and dropped.  I'm trying to find some way to have the second field update and do a _SplitPath when a file is dragged into the first field.

(Less importantly, I'd like to find a way to have the second input update if the first field losses focus - for those users manually entering path & file in the first field.)

Any help or a point in the right direction would be amazing.  Thanks.