Adding Scene/Item to a graphicView which was created using the design mode

[tuerahyosua]

Hi everyone. I am a newbie in Qt and I have a question.

So I created a new project of QMainWindows. Then I go directly to Forms -> mainwindow.ui and drag Graphics View into the main window. The next thing that I want to do is to add a rectangle inside the graphicView (name of the QGraphicView object) and make it move around just as I want it to be. Any suggestions on how to do that?

I want to make the animation inside the MainWindow, not in another window. I have tried creating scene and trying to put in by code in the mainwindow.cpp (as below), but it doesn't work. If i was able to put the rectangle into the scene/view, i can move to animating the rectangle. But i'm still stuck here.

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
 
    //create a scene
    QGraphicsScene * scene = new QGraphicsScene();
 
    //create the rectangle
    QGraphicsRectItem * rect = new QGraphicsRectItem();
    rect->setRect(0,0,50,50);
 
    //add the item into the scene
    scene->addItem(rect);
 
    //use the view from the mainwindow
    graphicsView = new QGraphicsView(scene);
    graphicsView.show();
 
}

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

    //create a scene
    QGraphicsScene * scene = new QGraphicsScene();

    //create the rectangle
    QGraphicsRectItem * rect = new QGraphicsRectItem();
    rect->setRect(0,0,50,50);

    //add the item into the scene
    scene->addItem(rect);

    //use the view from the mainwindow
    graphicsView = new QGraphicsView(scene);
    graphicsView.show();

}

To copy to clipboard, switch view to plain text mode 

I have randomly tried including "ui_mainwindow.h" but it still doesn't work. Haha