How to disable the default contex menu on the left corner of titlebar?

Hello,thanks for your help in advance!
I want to display the close button on the right of the title bar(which is show as "X") and disable the default contex menu.When I try "setWindowFlags( Qt :: WindowStaysOnTopHint | Qt::WindowTitleHint | Qt::CustomizeWindowHint );" the default contex menu can't popup when I press the touch screen,But the close button also disappear.And then I try "setWindowFlags( Qt :: WindowStaysOnTopHint | Qt::WindowTitleHint | Qt::CustomizeWindowHint | Qt::WindowCloseButtonHint );",The close button shows and the default contex menu is also actived!
How can I solve the problem?