Connecting tableWidget signal and external slot

[Zlatomir]

You must use the cellDoubleClick(int, int) signal of your tableWidget object.

So, if your tableview member is public, the connect should look something like:
QObject::connect( window->Your_tableWidget_name, SIGNAL(cellDoubleClicked(int, int)),
window, SLOT(onCellClicked(int, int))
);

But most likely the tableWidget is private (or the ui object or pointer is private, depends on your project), then you can create another signal in your mainwindow class, connect the cellDoubleClicked(int, int) signal with the signal you create (you can connect two signals) and use this signal to finally connect to the slot that you need to execute.