Getting an error with this, tried what you said...
Unable to cast object of type 'Dynamics.AX.Application.SalesCalcAvailableDlvDates_SalesLine' to type 'Dynamics.AX.Application.FormRun'.
this FormRun formB = sender.formRun() as FormRun; is returning SalesCalcAvailableDlvDates_SalesLine.
I still don't get how to represent the formA. I apologize for this.
Do you have any articles/resources regarding this? I am really having a hard time understanding the process on how to call formA from formB.