QDockWidget  *frame          = new QDockWidget ;
QGridLayout *frameLayout = new QGridLayout(frame);
QWidget* child                      = new QWidget; 
frameLayout->addWidget(child);
或者
QDockWidget  *frame          = new QDockWidget ;
QGridLayout *frameLayout = new QGridLayout;
QWidget* child                      = new QWidget; 
frameLayout->addWidget(child);
frame->setLayout (frameLayout);