How to click and pop up submenu

[shihao]

Hello, what I want to do is merely pop up a sub-menu when I click on a button.

connect(mybutton2, SIGNAL(clicked()), this, SLOT(call()));

connect(mybutton2, SIGNAL(clicked()), this, SLOT(call()));

To copy to clipboard, switch view to plain text mode 

The code above unable to do so. Does anybody knows how to do it?