void Demo::on_pushButton_clicked(){   
    QGridLayout * mainLayout= new QGridLayout(ui->groupBox); 
   QLineEdit *tl;    QPushButton *tb;
    for(int i=0;i<3;i++)  
  {    
        tl=new QLineEdit(ui->groupBox);
        QString str("防区%1"); 
       tb=new QPushButton(str.arg(i),ui->groupBox); 
 //  tb=new QPushButton(tr("防区%1").arg(i),ui->groupBox);
 //可以在此连接button的事件处理信号槽 
------这个地方怎么给每个组件添加信号和槽呢?
    mainLayout->addWidget(tl, i, 0);
    mainLayout->addWidget(tb, i, 1);
}  
  ui->groupBox->setLayout(mainLayout);}