About Qwtplots from other than main.cpp

Hi,
I am a newbie for Qwt. My requirement is to plot Simple plots ie Temperature Vs Time in my application using Qt 5.11.1 and later on RHEL 7 .3and RHEL 8.
I came across the Qwt libraries and felt it will do the job. I am able to compile and run the example projects like simpleplot.pro.
When I call the same code to run on the click of a button or even on a timers timeout slot from my application(not in main.c), i am not getting the plot displayed. There are no compilation errors.
I feel i am missing something at a very fundamental level since I just started on Qwt. Maybe someone can send a working code wherein the simpleplot curve gets called from a user press event like a click of a button (or other QtWidget or Timers timeout slot )and plots the graph.
Many thanks in advance. Waiting to get some positive response please.

:(
bltr