How to delete an already existing widget layout
I want to change QWidget layout
Ticker* pTicker = new Ticker(this);
The program has unexpectedly finished.
No, you are trying to modify/delete a QMainWindow layout which is not the same thing. Just don't try do that, QMainWindow's layout is a special layout to handle all its components (dock, status bar, tool bar etc.) . If you don't want it, just don't use a QMainWindow.
If you still need a QMainWindow, your custom widget should go in as the central widget (with setCentralWidget) So you have to at least create a container widget like I wrote "here":http://qt-project.org/forums/viewthread/49120/P15/