QDialog *dlg = new QDialog;
firstUi.setupUi(dlg);
dlg->exec();
connect(firstUi.pushButton1,SIGNAL(clicked()),this,SLOT(gotoad()));
connect(firstUi.pushButton2,SIGNAL(clicked()),this,SLOT(gotousr()));
connect(firstUi.pushButton3,SIGNAL(clicked()),this,SLOT(close()));
connect(secondUi.pushButton1,SIGNAL(clicked()),this,SLOT(adlogin()));
connect(thirdUi.pushButton1,SIGNAL(clicked()),this,SLOT(usrlogin()));
//说明
firstUi调用setupUi(dlg);已经创建
secondUi和thirdUi还没有创建