qt的buttonBox

#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include <QAbstractButton>
#include <QPushButton>
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
private:
Ui::MainWindow *ui;
private:
QPushButton *Clear;
private slots:
void on_buttonBox_clicked(QAbstractButton *button);};
#endif // MAINWINDOW_H
// → Go to slots
//       mainwindow.cpp
#include "mainwindow.h"
#include "ui_mainwindow.h"
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
}
MainWindow::~MainWindow()
{
delete ui;
}//       mainwindow.cpp
/***      ***/
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
Clear = new QPushButton; //new QPushButton
Clear->setText("Clear");//    Clear   Text
ui->buttonBox->addButton(Clear,QDialogButtonBox::ActionRole);
}
//       mainwindow.cpp
on_buttonBox_clicked(QAbstractButton*button)
/***  buttonBox  ***/
void MainWindow::on_buttonBox_clicked(QAbstractButton*button)
{
QString str;
str = ui->textEdit->toPlainText();
if(button == ui->buttonBox->button(QDialogButtonBox::Ok))
{
if(!ui->lineEdit->text().isEmpty())
{
str += ui->lineEdit->text()+" n";
ui->textEdit->setPlainText(str); //    textEdit
}
}
else if(button == this->Clear)
{
ui->textEdit->setPlainText("");//    textEdit
}
}