Window not showing up using show()

nestorac

I have some code for opening a window from the main one, but it doesn't work. "Window open." gets printed, then nothing else happens, it's just as if show() didn't do anything. This is invoked from a menu using a connector and an action.

The relevant code:

void test1::openNewWindow()
{
qWarning( "Window open." );

QWidget w(this);
Ui::dialog ventanados;
ventanados.setupUi(&w);
w.setWindowModality(Qt::ApplicationModal);
w.show();
}

Hi! The problem is that you create the window on the stack inside openNewWindow(), so it gets destroyed immediately when the function returns.

void test1::openNewWindow()
{
qWarning( "Window open." );

QWidget w(this); // <-- w is local to this scope
Ui::dialog ventanados;
ventanados.setupUi(&w);
w.setWindowModality(Qt::ApplicationModal);
w.show(); 
} // <-- scope ends, w gets destroyed

nestorac

@Wieland thank you. I have tried it and it is an excellent answer, but I don't still get the clue. I have added a 1sec delay to the function after calling show() to see if the windows appears, no luck. I have made the changes you have proposed, and I now have the following code:

test1.h

#ifndef test1_H
#define test1_H

#include <QMainWindow>
#include <QWidget>

#include "ui_test1.h"

class test1 : public QMainWindow
{
    Q_OBJECT

public:
    test1();
    
public slots:
   void openNewWindow();
   
private:
    QWidget *w;
    Ui::dialog ventanados;
};

#endif // test1_H

test1.cpp

#include "test1.h"

#include <QLabel>
#include <QMenu>
#include <QMenuBar>
#include <QAction>
#include <QDialog>
#include <QtTest/QTest>

test1::test1()
{
    w = new QWidget(this);
    QLabel* label = new QLabel( this );
    label->setText( "Hello World!" );
    setCentralWidget( label );
    QAction* action = new QAction(this);
    action->setText( "Open new window" );
    connect(action, SIGNAL(triggered()), SLOT(openNewWindow()) );
    menuBar()->addMenu( "File" )->addAction( action );
}

void test1::openNewWindow()
{
    ventanados.setupUi(w);
    w->show();
    QTest::qSleep(1000);
}

The following creates a widget that is a child of your MainWindow:

w = new QWidget(this);

If you want w to be a window on its own, then call the constructor without a parent:
w = new QWidget();

nestorac

OMG, thanks!!!

Chris Kawa

Parents are important for stacking order and focus management. What's more is in your code you're not deleting it explicitly, so if you don't give it a parent it will leak.
Better than not giving it a parent would be to either use QDialog instead or make it a window via a flag, i.e.:

w = new QWidget(this, Qt::Window);

nestorac

It also works! Thank you.