how to change 1st mainwindow's frame by 2nd window's frame

[doubw]

Hi,

i'm new in qt. and i have a minwindow and a second window. the 1st window has 3 frames and the 2nd has only one. my question: how to swap after clicked a button the 2nd window's frame with the 3rd frame of the 1st window? here are my codes:

.h
#ifndef FIRSTDIALOG_H
#define FIRSTDIALOG_H
 
#include <QDialog>
#include <QFrame>
#include <QWidget>
#include <QListWidgetItem>
 
namespace Ui {
class FirstDialog;
}
 
class FirstDialog : public QDialog
{
    Q_OBJECT
 
public:
    explicit FirstDialog(QWidget *parent = 0);
    ~FirstDialog();
 
private:
    Ui::FirstDialog *ui;
    QFrame *frame_4;
};
 
#endif // FIRSTDIALOG_H
 
//---------------------------------------------
.cpp
#include "firstdialog.h"
#include "ui_firstdialog.h"
#include <QWidget>
 
FirstDialog::FirstDialog(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::FirstDialog)
{
    ui->setupUi(this);
}
 
FirstDialog::~FirstDialog()
{
    delete ui;
}

.h
#ifndef FIRSTDIALOG_H
#define FIRSTDIALOG_H
 
#include <QDialog>
#include <QFrame>
#include <QWidget>
#include <QListWidgetItem>
 
namespace Ui {
class FirstDialog;
}
 
class FirstDialog : public QDialog
{
    Q_OBJECT
 
public:
    explicit FirstDialog(QWidget *parent = 0);
    ~FirstDialog();
 
private:
    Ui::FirstDialog *ui;
    QFrame *frame_4;
};
 
#endif // FIRSTDIALOG_H
 
//---------------------------------------------
.cpp
#include "firstdialog.h"
#include "ui_firstdialog.h"
#include <QWidget>
 
FirstDialog::FirstDialog(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::FirstDialog)
{
    ui->setupUi(this);
}
 
FirstDialog::~FirstDialog()
{
    delete ui;
}

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.h
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
 
#include <QMainWindow>
#include <QLabel>
//#include <QListWidget>
//#include <QWidget>
#include <QListWidgetItem>
 
namespace Ui {
class MainWindow;
}
 
class MainWindow : public QMainWindow
{
    Q_OBJECT
 
public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();
 
private slots:
    void on_pushButton_1_clicked();
 
private:
    Ui::MainWindow *ui;
    QFrame *frame_1;
    QFrame *frame_2;
    QFrame *frame_3;
};
 
#endif // MAINWINDOW_H
//-------------------------------------------
.cpp
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "firstdialog.h"
#include <QLabel>
#include <QPixmap>
 
MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    QPixmap pix("C:/Users/Infonet/Documents/frames_test/logo6_DT.png");
    int w = ui->label_1->width();
    int h = ui->label_1->height();
    ui->label_1->setPixmap(pix.scaled(w,h,Qt::KeepAspectRatio));
}
 
MainWindow::~MainWindow()
{
    delete ui;
}
 
void MainWindow::on_pushButton_1_clicked()
{
 FirstDialog *firstdia = new FirstDialog;
 firstdia->show();
}

.h
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
 
#include <QMainWindow>
#include <QLabel>
//#include <QListWidget>
//#include <QWidget>
#include <QListWidgetItem>
 
namespace Ui {
class MainWindow;
}
 
class MainWindow : public QMainWindow
{
    Q_OBJECT
 
public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();
 
private slots:
    void on_pushButton_1_clicked();
 
private:
    Ui::MainWindow *ui;
    QFrame *frame_1;
    QFrame *frame_2;
    QFrame *frame_3;
};
 
#endif // MAINWINDOW_H
//-------------------------------------------
.cpp
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "firstdialog.h"
#include <QLabel>
#include <QPixmap>

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    QPixmap pix("C:/Users/Infonet/Documents/frames_test/logo6_DT.png");
    int w = ui->label_1->width();
    int h = ui->label_1->height();
    ui->label_1->setPixmap(pix.scaled(w,h,Qt::KeepAspectRatio));
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::on_pushButton_1_clicked()
{
 FirstDialog *firstdia = new FirstDialog;
 firstdia->show();
}

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thanks.