只有addrow,我测试用一下方法
QWidget*w = new QWidget();
    this->setCentralWidget(w);
     QFormLayout* fl = new QFormLayout(this);
     w->setLayout(fl);
     QLineEdit*txt = new QLineEdit(this);
     fl->addRow(tr("aaaaaaaa"),txt);
     fl->removeItem(fl->itemAt(0));
     delete txt;
     QComboBox *drparg = new QComboBox(this);
     fl->addRow(tr("bbbbbbbbbb"),drparg);
这样楞写,惯用,但是放到程序内,就不管用了,在程序内我总是删除fl->itemAt(3)