QGraphicsView doesn't close when MainWindow is closed.

Peter_Dev

Hello, everyone.
I need to access QGraphicsView from different functions of MainWindow, so i declared it in header file like:

QGraphicsScene scene;
QGraphicsView view;
QGraphicsItem item;

it works properly, but when i close main window, graphics view is still open and in application output program finishes after i close this graphics view. Well, that's also not bad, but i'd like graphics view window be closed automatically after i close main window. How can i make it?

JonB

@Peter_Dev
If you keep it separate, you really just have two distinct, top-level windows, with no link between them. The main window cannot have a "parent-child" relationship to the gfx view window.

You could fiddle around with the gfx view as a modeless dialog, but I don't; think that is right/would help.

So far as I know, you cannot have a relationship between these two independent, top-level windows. No automatic closing of the gfx view when you close the main window (or vice versa!).

That means you must write code overriding main window's close event which explicitly closes the gfx view, e.g.:

void MainWindow::closeEvent(QCloseEvent *event)
{
    view.close();
    QMainWindow::closeEvent(event);
}

Having your separate gfx window has consequences for the native windowing system. You will see both windows showing up in your windowing manager's "open program windows taskbar". Which may or may not what you intend.

but keep it in separate window and keep it accessible to any function in Mainwindow?

Kind of depends what you mean by "accessible to any function". You can still access it via your view member variable. But it's not a part of the main window.

JSher

Did you set MainWindow as parent? perhaps post more code.

--James

Peter_Dev

@JSher
Thanks for your reply)
header file

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QGraphicsScene>
#include <QGraphicsPixmapItem>
#include <QGraphicsView>


QT_BEGIN_NAMESPACE

namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);

    QGraphicsScene scene;
    QGraphicsView view;
    QGraphicsPixmapItem item;


    ~MainWindow();


private:
    Ui::MainWindow *ui;
};
#endif // MAINWINDOW_H

cpp

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{

 view.setScene(scene);
    view.setFixedSize(602,602);

    scene.addItem(&item);
}

later in function of MainWindow i do

item.setPixmap(QPixmap(path_to_image));

        view.show();

JonB

@Peter_Dev
I don't see that you have placed the QGraphicsView view; anywhere on the MainWindow? It's just floating around visibly in a random place, with no connection to the main window

Cobra91151

@Peter_Dev

Hello!

You need to remove: view.show(); because it will create additional window, and set the parent: view.setParent(this); before the view.setScene(scene); scene initialization.

JonB

@Cobra91151
If that's all you do, where (on the main window) will this QGraphicsView view actually show up? [I know it will be at (0, 0), but that's not what I'm getting at.]

Peter_Dev

This post is deleted!

JonB

@Peter_Dev
I know it does! I am asking if that is your intention? EDIT You have just deleted your post saying it shows up in a separate window :(

If it is, do you put other stuff on your main window? And is your intention that this separate graphics view window should be a modeless, separate window, but you would like it to close when the main window closes?

Cobra91151

@JonB @Peter_Dev

Hello!
You are right. To add QGraphicsView to the main window:

Code:

MainWindow::MainWindow(QWidget *parent)
  : QMainWindow(parent)
  , ui(new Ui::MainWindow)
{
      QWidget *mainWidget = new QWidget(this);
      setCentralWidget(mainWidget);
      QGraphicsScene *scene = new QGraphicsScene(mainWidget);
      scene->addLine(10, 10, 100, 100);
  
      QGraphicsView *view = new QGraphicsView(scene);
      view->setFixedSize(500, 300);
  
      QHBoxLayout *testLayout = new QHBoxLayout();
      testLayout->addWidget(view);
      mainWidget->setLayout(testLayout);
}

The example code will draw the simple line and display it on the main window.

Peter_Dev

@JonB Sorry, i deleted that post because i thougth you were asking me, when you were asking Cobra91151. Qraphics view shows up in it's own window. Is there a way to connect graphics view to mainwindow, but keep it in separate window and keep it accessible to any function in Mainwindow?

JonB

@Cobra91151
Yes; or the OP could just this->setCentralWidget(view)if he wanted that widget alone in the main window. However, we now know that he actually does want it as a separate window, just he wants to control its closure, which I'm answering now....

JonB

@Peter_Dev
If you keep it separate, you really just have two distinct, top-level windows, with no link between them. The main window cannot have a "parent-child" relationship to the gfx view window.

You could fiddle around with the gfx view as a modeless dialog, but I don't; think that is right/would help.

So far as I know, you cannot have a relationship between these two independent, top-level windows. No automatic closing of the gfx view when you close the main window (or vice versa!).

That means you must write code overriding main window's close event which explicitly closes the gfx view, e.g.:

void MainWindow::closeEvent(QCloseEvent *event)
{
    view.close();
    QMainWindow::closeEvent(event);
}

Having your separate gfx window has consequences for the native windowing system. You will see both windows showing up in your windowing manager's "open program windows taskbar". Which may or may not what you intend.

but keep it in separate window and keep it accessible to any function in Mainwindow?

Kind of depends what you mean by "accessible to any function". You can still access it via your view member variable. But it's not a part of the main window.

Peter_Dev

@JonB Thanks a lot! That works exactly as i wanted! But is it safe to do like that? May some processes still running in background after closing?

Cobra91151

@Peter_Dev

Also, you can try to create the additional dialog, which will contain the QGraphicsView and display dialog when main window launches. To connect between them, you can use signal and slots: https://doc.qt.io/qt-5/signalsandslots.html. When the main window closes, then it will close the second dialog automatically.

Code:

graphicstest.h

#ifndef GRAPHICSTEST_H
#define GRAPHICSTEST_H

#include <QMainWindow>
#include "seconddlg.h"

class GraphicsTest : public QMainWindow
{
    Q_OBJECT

public:
    GraphicsTest(QWidget *parent = nullptr);
    ~GraphicsTest();
};
#endif // GRAPHICSTEST_H

graphicstest.cpp

#include "graphicstest.h"

GraphicsTest::GraphicsTest(QWidget *parent)
    : QMainWindow(parent)
{
    setWindowTitle("Main Window");
    setFixedSize(400, 300);
    SecondDlg *sDlg = new SecondDlg(this);
    sDlg->show();
}

GraphicsTest::~GraphicsTest()
{
}

seconddlg.h

#ifndef SECONDDLG_H
#define SECONDDLG_H

#include <QDialog>
#include <QGraphicsScene>
#include <QGraphicsView>
#include <QHBoxLayout>

namespace Ui {
class SecondDlg;
}

class SecondDlg : public QDialog
{
    Q_OBJECT

public:
    explicit SecondDlg(QWidget *parent = nullptr);
    ~SecondDlg();

private:
    Ui::SecondDlg *ui;
};

#endif // SECONDDLG_H

seconddlg.cpp

#include "seconddlg.h"
#include "ui_seconddlg.h"

SecondDlg::SecondDlg(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::SecondDlg)
{
    ui->setupUi(this);
    setWindowTitle("QGraphicsView dialog");
    setMinimumSize(600, 400);
    setWindowFlags(Qt::Dialog | Qt::MSWindowsFixedSizeDialogHint | Qt::WindowCloseButtonHint);
    QGraphicsScene *scene = new QGraphicsScene(this);
    scene->addLine(10, 10, 100, 100);

    QGraphicsView *view = new QGraphicsView(scene);
    view->setFixedSize(500, 300);

    QHBoxLayout *testLayout = new QHBoxLayout();
    testLayout->addWidget(view);
    setLayout(testLayout);
}

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

Screenshot:

Peter_Dev

@Cobra91151 Thank you for support! That's also a very good solution!)

JonB

@Cobra91151
That's what I meant by "doing it with modeless dialog". If it works it's simpler because you don't have to explicitly close. But I thought when I tried it there were problems.

In your example, if you drag the windows so they overlap can user still click either one up-front? And if the main window has content widgets you can interact with them freely? I recall problems, but I may (well) be getting confused!

Cobra91151

@JonB

Yes, you can interact with them, but second dialog overlaps the main window: alt text .

JonB

@Cobra91151
Ah ha! I thought I had some recollection of issues like this, So they are not truly independent, the graphics view would always be atop the main window. Which may not be the behaviour desired by @Peter_Dev , I don't know.