Using QList data from other .cpp file

[Santosh Reddy]

Are you referring to the same QList from both processingfile.cpp and mainwindow.cpp?

Also you should declare as "QList<FinalData> finaldata" in processingfile.cpp
and
declare as "extern QList<FinalData> finaldata" in mainwindow.cpp, note the extern keyword.

I'm sure the QList is populated as i've tried to print out the data in the QList using qDebug in the cpp file which i've processed the data.

You need to check/print the QList just before the painting/plotting in the mainwidow.cpp