Qt login，自动识别焦点

代码说明：

#include "mainwindow.h" #include "ui_mainwindow.h" MainWindow::MainWindow(QWidget *parent) :     QMainWindow(parent),     ui(new Ui::MainWindow) {     ui->setupUi(this);     pushButton = new QPushButton(this);     pushButton->setObjectName(QString::fromUtf8("pushButton"));     pushButton->setGeometry(QRect(40, 180, 51, 27));     pushButton_2 = new QPushButton(this);     pushButton_2->setObjectName(QString::fromUtf8("pushButton_2"));     pushButton_2->setGeometry(QRect(40, 140, 51, 27));     pushButton_3 = new QPushButton(this);     pushButton_3->setObjectName(QString::fromUtf8("pushButton_3"));     pushButton_3->setGeometry(QRect(100, 140, 51, 27));   &