The problem occurs when I decided to move the dialog to other screen position. There is no problem with the initial setup and execution. BUT, as soon as I move the main dialog to another screen position AND execute, the sub-dialog remains on the initial setup position. (This means that it does not attached together with the main dialog, which is the problem)

Thus, I believe that I am lacking on the skill to 'bridge'/link values OR at least finding the 'moved'/updated position value into the setGeometry or position setting function. Please look at my code for clarity :) Thank you and looking forward for the community help.

//mainwindow.h
#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QPropertyAnimation>
#include "SubDisplay_1.h"

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

    void AdjustGeometryFunc(int SDposx = 300, int SDposy=300, int SDwidth=0, int SDheight=0);

private:
    Ui::MainWindow *ui;

    QPropertyAnimation *animation;

private slots:
    void openPanel();
};

#endif // MAINWINDOW_H

//Sub_Display_1.h
#ifndef SubDisplay_1_H
#define SubDisplay_1_H

#include <QDialog>
#include <QPropertyAnimation>
#include <QTimer>
#include "mainwindow.h"

namespace Ui {
class SubDisplay_1;
}

class SubDisplay_1 : public QDialog
{
    Q_OBJECT

public:
    explicit SubDisplay_1(QWidget *parent = 0);
    ~SubDisplay_1();

private slots:
    void panelMovementToOri();

private:
    Ui::SubDisplay_1 *ui;
    bool marker = 0;

    SubDisplay_1 *Secdialog;
    QTimer *tim;

    int initialxpos;
    int initialypos;
    int finalxpos;
    int finalypos;
};

#endif // SubDisplay_1_H

//main.cpp
#include "mainwindow.h"
#include <QApplication>

int main(int argc, char *argv[])
{
  QApplication a(argc, argv);
  MainWindow w;
  w.show();

  return a.exec();
}

//mainwindow.cpp
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "SubDisplay_1.h"
#include "SubDisplay_2.h"

#include <QDebug>


MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    MainWindow::AdjustGeometryFunc();
    connect(ui->pushButton_1,SIGNAL(released()),this,SLOT(openPanel()));
    connect(ui->pushButton_2,SIGNAL(released()),this,SLOT(openPanel()));
}

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

void MainWindow::AdjustGeometryFunc(int SDposx, int SDposy, int SDwidth, int SDheight){
    MainWindow::setGeometry(SDposx, SDposy, this->width(),this->height());
    qDebug() << "SDposx" << SDposx;
    qDebug() << "SDposy" << SDposy;
}

void MainWindow::openPanel()
{
    QPushButton * button = (QPushButton*)sender();
    if (button->text() == "pushbutton_1"){
    SubDisplay_1 SecDialog(this);
    SecDialog.setModal(false);
    SecDialog.exec();

    int initialxpos = MainWindow::frameGeometry().x();
    int initialypos = MainWindow::frameGeometry().y();
    qDebug() << "initialxpos" << initialxpos; //this position value will update
    qDebug() << "initialypos" << initialypos; //this position value will update

    }
}

//SubDisplay_1.cpp
#include "SubDisplay_1.h"
#include "ui_SubDisplay_1.h"
#include "mainwindow.h"

#include <QTimer>
#include <QDebug>

SubDisplay_1::SubDisplay_1(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::SubDisplay_1)
{
    ui->setupUi(this);

    MainWindow mw;
    initialxpos = mw.frameGeometry().x(); //PROBLEM: this is not updated. remain with initial setup value
    initialypos = mw.frameGeometry().y(); //PROBLEM: //PROBLEM: this is not updated. remain with initial setup value
    finalxpos = initialxpos - SubDisplay_1::width();
    finalypos = initialypos;

    qDebug() << "Subinitialxpos" << initialxpos;
    qDebug() << "Subinitialypos" << initialypos;

    tim = new QTimer;
    tim->setInterval(1900);
    tim->start();

    if(marker==0)
        {
            QPropertyAnimation *animation = new QPropertyAnimation(this, "geometry");
            animation->setDuration(5000);
            animation->setStartValue(QRect(initialxpos, initialypos, this->width(), this->height()));
            animation->setEndValue(QRect(finalxpos, finalypos, this->width(), this->height()));
            animation->start();
            marker = 1;
        }

    connect(ui->pushButton_5,SIGNAL(released()),this,SLOT(panelMovementToOri()));
}

void SubDisplay_1::panelMovementToOri(){
    if (marker==1)
        {

            QPropertyAnimation *animation = new QPropertyAnimation(this, "geometry");
            animation->setDuration(5000);
            animation->setStartValue(QRect(finalxpos, finalypos, this->width(), this->height()));
            animation->setEndValue(QRect(initialxpos, initialypos, this->width(), this->height()));
            animation->start();
            marker = 0;
            connect(tim,SIGNAL(timeout()),this,SLOT(close()));
        }
}

SubDisplay_1::~SubDisplay_1()
{
    delete ui;
}