方法1，删除centralWidget后，添加手动部分内容。

    left = new QPushButton("killin kind");
    right = new QPushButton("Emma");

    if(this->centralWidget())    {

       delete this->centralWidget();

    }   else    {    }

    QHBoxLayout *hLayout= new QHBoxLayout;
    QWidget *cWidget = new QWidget(this);
 this->setCentralWidget(cWidget)；

    hLayout->addWidget(left)；
  hLayout->addWidget(right);
    hLayout->addWidget(labelPos)；
    cWidget->setLayout(hLayout);