Qt Application with layout's, QPushButton and QGraphicsItem

Question

I am trying to draw various shapes like rectangle, ellipse, text etc uisng QGraphicsView and QGraphicsScene. For that I am trying to create an interface where there will be a vertical layout and besides that there will be few buttons. On clicking those buttons, I can show various QGraphicsItem's on screen. I want to create this interface programatically but not using ui.
I tried and ended up this way.

I wanted buttons on the right side and verticalLayout on the left side and both should filled up the whole screen.
Here is my current implementation :

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

    QGraphicsScene* scene = new QGraphicsScene(this);

    QGraphicsView* view = new QGraphicsView(this);
    view->setScene(scene);

    QWidget* mainWidget = new QWidget(this);
    QHBoxLayout *mainLayout = new QHBoxLayout();

    QVBoxLayout *buttonLayout = new QVBoxLayout();
    QVBoxLayout *vlayout2 = new QVBoxLayout();

    vlayout2->addWidget(view);

    QPushButton *btn1 = new QPushButton("Rectangle");
    btn1->setSizePolicy( QSizePolicy::Expanding, QSizePolicy::Preferred );
    
    QPushButton *btn2 = new QPushButton("Ellipse");
    btn2->setSizePolicy( QSizePolicy::Expanding, QSizePolicy::Preferred );
    
    QPushButton *btn3 = new QPushButton("Text");
    btn3->setSizePolicy( QSizePolicy::Expanding, QSizePolicy::Preferred );

    buttonLayout->addWidget(btn1);
    buttonLayout->addWidget(btn2);
    buttonLayout->addWidget(btn3);
    buttonLayout->addStretch();

    mainLayout->addLayout(buttonLayout);
    mainLayout->addLayout(vlayout2);

    mainWidget->setLayout(mainLayout);
}    

Can anyone guide me ?

Answer 1

Actually, it should work with the hints given in my comments.

I made an MCVE to convince myself:

#include <QtWidgets>

int main(int argc, char **argv)
{
  qDebug() << "Qt Version:" << QT_VERSION_STR;
  QApplication app(argc, argv);
  // setup GUI
  QWidget qMain;
  qMain.setWindowTitle("Test Box Layout");
  qMain.resize(640, 320);
  QHBoxLayout qHBox;
  QVBoxLayout qVBoxBtns;
  QPushButton qBtnRect("Rectangle");
  qVBoxBtns.addWidget(&qBtnRect);
  QPushButton qBtnCirc("Circle");
  qVBoxBtns.addWidget(&qBtnCirc);
  QPushButton qBtnText("Text");
  qVBoxBtns.addWidget(&qBtnText);
  qVBoxBtns.addStretch();
  qHBox.addLayout(&qVBoxBtns);
  QVBoxLayout qVBoxView;
  QGraphicsView qView;
  qVBoxView.addWidget(&qView, 1);
  qHBox.addLayout(&qVBoxView, 1);
  qMain.setLayout(&qHBox);
  qMain.show();
  // runtime loop
  return app.exec();
}

Output:

Thus, there must be something else in OP's code…

Unfortunately, OP didn't expose an MCVE. Thus, it's not clear how OP's Widget is instanced. Is it the widget which becomes the main window? Is there another widget where the Widget's instance becomes child of?

It's just guessing but the latter would explain what OP described.

---

To confirm my guess, I modified the above code a bit:

  // setup GUI
  QWidget qMain0; // main window widget
  QWidget qMain(&qMain0); // child widget of main window widget

⋮

  qMain.setLayout(&qHBox);
  qMain0.show();
  // runtime loop
  return app.exec();

Please, note that qMain is now a child of qMain0 but there is no layout which adjusts the size of qMain when qMain0 is resized.

Hence, the size of view stays the initial size while the window is resized.