Switching between two ui forms / QMainWindow screens

[d_stranz]

This I temp resolved by deriving the ui classes from QMainWindow instead of QWidget.

Do you understand that QMainWindow is supposed to be the only top-level window in your app, and that there is only supposed to be one instance of that class? You now have THREE classes that are derived from QMainWindow. QMainWindow is not a magic bullet class that you can derive anything from just to achieve some desired UI effect (like a different background color). And showMaximized() should never be called on a child window, only on a top-level window like QMainWindow.

QMainWindow is not just a widget, it defines a framework and a set of behaviors for applications with a single top-level window and many child windows within it. You cannot just simply use a QMainWindow anywhere you want without running into problems somewhere along the line because you haven't followed the rules.

I have no idea what types of classes "RaptorLrsGUI" and "RaptorCoreGUI" are. If they aren't derived from QWidget, then that is an error. If you have a custom paintEvent() in these classes, then that is where you should implement the code to fill the background with whatever color you want. If you do not have a paintEvent(), then in the constructor for these classes you should have code like this:

QPalette pal = palette();  // retrieves the default palette for the widget, as defined by the app's style
pal.setColor( QPalette::Window, Qt::white );
setPalette( pal );
 
setAutoFillBackground( true );

QPalette pal = palette();  // retrieves the default palette for the widget, as defined by the app's style
pal.setColor( QPalette::Window, Qt::white );
setPalette( pal );

setAutoFillBackground( true );

To copy to clipboard, switch view to plain text mode 

Setting the appropriate colors in the palette as well as ensuring that the widget automatically clears its background and fills it with the chosen color on a paintEvent() is the right way to do it.

I think you need to take a step back and look at some of the many examples in Qt for QMainWindow-based apps. If you continue down the path you are taking, your PoC is going to turn out to be a "proof of buggy code" that acts in ways you can't explain and is confusing to debug.

[nitks.abhinav]

Hi,
I very well know that QMainWindow is top level/parent window. That's what initially I did, when classes "RaptorLrsGUI" and "RaptorCoreGUI" are derived from QWidget and QStackedWidget is used , I don't see anything on screen, it goes blank. The below code is exactly as per suggested and it does not work.
Also I have changed the code to remove showMaximized on widget and use single shot timer.

Thanks for your patience..:-)

Base::Base(QWidget *parent) : QMainWindow(parent, Qt::FramelessWindowHint)
{
       qDebug() << "Base CTOR called\n";
 
       QPalette pal = palette();  // retrieves the default palette for the widget, as defined by the app's style
       pal.setColor( QPalette::Window, Qt::white );
       setPalette( pal );
 
       setAutoFillBackground( true );
 
       //Show the first screen, loading raptor status       
       lrsGUI = new RaptorLrsGUI;                                                   //RaptorLrsGUI derived from QWidget
       lrsGUI->setlabel(QString("Loading Raptor Status..."));
       coreGUI = new RaptorCoreGUI;                                             //RaptorCoreGUI derived from QWidget
 
       stackedWidget = new QStackedWidget();       
       stackedWidget->addWidget(lrsGUI);
       stackedWidget->addWidget(coreGUI);
 
       stackedWidget->setCurrentIndex(0);       
}
 
Base::~Base()
{
    qDebug() << "Main Thread: destroying base objects \n";
    delete lrsGUI;
    delete coreGUI;
    delete stackedWidget;
}
 
 
void Base::rcvInitData()
{
    qDebug()<< "Main Thread (CALLBACK): Display second screen\n";
    stackedWidget->setCurrentIndex(1);
}

Base::Base(QWidget *parent) : QMainWindow(parent, Qt::FramelessWindowHint)
{
       qDebug() << "Base CTOR called\n";

       QPalette pal = palette();  // retrieves the default palette for the widget, as defined by the app's style
       pal.setColor( QPalette::Window, Qt::white );
       setPalette( pal );

       setAutoFillBackground( true );

       //Show the first screen, loading raptor status       
       lrsGUI = new RaptorLrsGUI;                                                   //RaptorLrsGUI derived from QWidget
       lrsGUI->setlabel(QString("Loading Raptor Status..."));
       coreGUI = new RaptorCoreGUI;                                             //RaptorCoreGUI derived from QWidget

       stackedWidget = new QStackedWidget();       
       stackedWidget->addWidget(lrsGUI);
       stackedWidget->addWidget(coreGUI);

       stackedWidget->setCurrentIndex(0);       
}

Base::~Base()
{
    qDebug() << "Main Thread: destroying base objects \n";
    delete lrsGUI;
    delete coreGUI;
    delete stackedWidget;
}


void Base::rcvInitData()
{
    qDebug()<< "Main Thread (CALLBACK): Display second screen\n";
    stackedWidget->setCurrentIndex(1);
}

To copy to clipboard, switch view to plain text mode 

Rest of the code remain same as earlier.

[d_stranz]

You create the QStackedWidget, but you do not give it any parent. You do not tell your QMainWidget to use the QStackedWidget as its "centralWidget". Thus the QStackedWidget is never shown, so it is always invisible.

Line 16 should be:

stackedWidget = new QStackedWidget( this );

stackedWidget = new QStackedWidget( this );

To copy to clipboard, switch view to plain text mode 

and add a line at the end of the constructor:

setCentralWidget( stackedWidget );

setCentralWidget( stackedWidget );

To copy to clipboard, switch view to plain text mode 

If you want the background of the Raptor* widgets to be white, this code needs to be moved to their constructors. It does nothing if you have it in the Base constructor:

QPalette pal = palette();  // retrieves the default palette for the widget, as defined by the app's style
       pal.setColor( QPalette::Window, Qt::white );
       setPalette( pal );

QPalette pal = palette();  // retrieves the default palette for the widget, as defined by the app's style
       pal.setColor( QPalette::Window, Qt::white );
       setPalette( pal );

To copy to clipboard, switch view to plain text mode 

Edit: Actually, maybe this is incorrect. If you set the palette before creating the stacked and Raptor* widgets, it is possible that they will inherit the QPalette:: Window setting from the Base class.

[nitks.abhinav]

I made the changes the but still I can see white screen with title bar (screenshot attached) , below is the complete code.

Thanks you for all the help,

/Second UI */
namespace Ui {
class RaptorCoreGUI;
}
 
class RaptorCoreGUI : public QWidget
{
    Q_OBJECT
 
public:
    explicit RaptorCoreGUI(QWidget *parent = 0);
    ~RaptorCoreGUI();
    void configInitData(bool);
    void setlabel(QString);
 
private:
    Ui::RaptorCoreGUI *ui;
};
 
/*First UI*/
amespace Ui {
class RaptorLrsGUI;
}
 
class RaptorLrsGUI : public QWidget
{
    Q_OBJECT
 
public:
    explicit RaptorLrsGUI(QWidget *parent = 0);
    ~RaptorLrsGUI();
    void setlabel(QString);
 
private:
    Ui::RaptorLrsGUI *ui;
};
 
/*Base class  derived from  QMainWindow*/
class Base : public QMainWindow
{
    Q_OBJECT
public:
   RaptorLrsGUI *lrsGUI;
   RaptorCoreGUI *coreGUI;
   QStackedWidget *stackedWidget;
   QVBoxLayout *layout;
  ~Base();
   explicit Base (QWidget *parent = 0);
 
 
private slots:
    void rcvInitData();
};
 
/*Second UI CPP*/
RaptorCoreGUI::RaptorCoreGUI(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::RaptorCoreGUI)
{
    ui->setupUi(this);
    this->setAutoFillBackground(true);
    this->setStyleSheet("background-color:white;");
}
 
RaptorCoreGUI::~RaptorCoreGUI()
{
    delete ui;
}
 
 
void RaptorCoreGUI::setlabel(QString label)
{
    qDebug() << "Main Thread(COREGUI): Setting Label\n";    
    ui->label->setText(label);
}
 
/*First UI cpp*/
RaptorLrsGUI::RaptorLrsGUI(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::RaptorLrsGUI)
{    
    ui->setupUi(this);
    this->setAutoFillBackground(true);
    this->setStyleSheet("background-color:white;");
}
 
RaptorLrsGUI::~RaptorLrsGUI()
{
    qDebug() << "Main Thread: destroying the ui object \n";
    delete ui;
}
 
void RaptorLrsGUI::setlabel(QString label)
{
    qDebug() << "Main Thread(LSRGUI): Setting Label\n";    
    ui->label->setText(label);
}
 
 
/*main.cpp*/
Base::Base(QWidget *parent) :
      QMainWindow(parent, Qt::FramelessWindowHint)
{
       qDebug() << "Base CTOR called\n";
 
       QPalette pal = palette();  // retrieves the default palette for the widget, as defined by the app's style
       pal.setColor( QPalette::Window, Qt::white );
       setPalette( pal );
 
       setAutoFillBackground( true );
 
 
       //Show the first screen, loading raptor status       
       lrsGUI = new RaptorLrsGUI;
       lrsGUI->setlabel(QString("Loading Raptor Status..."));
       coreGUI = new RaptorCoreGUI;
 
       stackedWidget = new QStackedWidget(this);
       stackedWidget->addWidget(lrsGUI);
       stackedWidget->addWidget(coreGUI);
 
       stackedWidget->setCurrentIndex(0);
       setCentralWidget(stackedWidget);
}
 
Base::~Base()
{
    qDebug() << "Main Thread: destroying base objects \n";
    delete lrsGUI;
    delete coreGUI;
    delete stackedWidget;
}
 
void Base::rcvInitData()
{
    qDebug()<< "Main Thread (CALLBACK): Display second screen\n";
    stackedWidget->setCurrentIndex(1);
}
 
//! [1]
int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
 
    //Instantiate base class    
    Base baseObj;
 
 
    //instantiate Client thread object
    ClientThread clientThread;
    qDebug() << "Connecting sendmsg and handle_callback1()\n";
    QObject::connect(&clientThread, SIGNAL(sendInitData()), &baseObj, SLOT(rcvInitData()), Qt::QueuedConnection);
 
    qDebug() << "Main Thread: starting clockThread\n";
    clientThread.start();
 
    app.exec();
    qDebug() << "Mian Thread: Quiting clockThread\n";
    clientThread.quit();
    qDebug() << "Main Thread: Waiting on clockThread \n";
    clientThread.wait();
    return 0;
}

/Second UI */
namespace Ui {
class RaptorCoreGUI;
}

class RaptorCoreGUI : public QWidget
{
    Q_OBJECT

public:
    explicit RaptorCoreGUI(QWidget *parent = 0);
    ~RaptorCoreGUI();
    void configInitData(bool);
    void setlabel(QString);

private:
    Ui::RaptorCoreGUI *ui;
};

/*First UI*/
amespace Ui {
class RaptorLrsGUI;
}

class RaptorLrsGUI : public QWidget
{
    Q_OBJECT

public:
    explicit RaptorLrsGUI(QWidget *parent = 0);
    ~RaptorLrsGUI();
    void setlabel(QString);

private:
    Ui::RaptorLrsGUI *ui;
};

/*Base class  derived from  QMainWindow*/
class Base : public QMainWindow
{
    Q_OBJECT
public:
   RaptorLrsGUI *lrsGUI;
   RaptorCoreGUI *coreGUI;
   QStackedWidget *stackedWidget;
   QVBoxLayout *layout;
  ~Base();
   explicit Base (QWidget *parent = 0);


private slots:
    void rcvInitData();
};

/*Second UI CPP*/
RaptorCoreGUI::RaptorCoreGUI(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::RaptorCoreGUI)
{
    ui->setupUi(this);
    this->setAutoFillBackground(true);
    this->setStyleSheet("background-color:white;");
}

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


void RaptorCoreGUI::setlabel(QString label)
{
    qDebug() << "Main Thread(COREGUI): Setting Label\n";    
    ui->label->setText(label);
}

/*First UI cpp*/
RaptorLrsGUI::RaptorLrsGUI(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::RaptorLrsGUI)
{    
    ui->setupUi(this);
    this->setAutoFillBackground(true);
    this->setStyleSheet("background-color:white;");
}

RaptorLrsGUI::~RaptorLrsGUI()
{
    qDebug() << "Main Thread: destroying the ui object \n";
    delete ui;
}

void RaptorLrsGUI::setlabel(QString label)
{
    qDebug() << "Main Thread(LSRGUI): Setting Label\n";    
    ui->label->setText(label);
}


/*main.cpp*/
Base::Base(QWidget *parent) :
      QMainWindow(parent, Qt::FramelessWindowHint)
{
       qDebug() << "Base CTOR called\n";

       QPalette pal = palette();  // retrieves the default palette for the widget, as defined by the app's style
       pal.setColor( QPalette::Window, Qt::white );
       setPalette( pal );

       setAutoFillBackground( true );


       //Show the first screen, loading raptor status       
       lrsGUI = new RaptorLrsGUI;
       lrsGUI->setlabel(QString("Loading Raptor Status..."));
       coreGUI = new RaptorCoreGUI;

       stackedWidget = new QStackedWidget(this);
       stackedWidget->addWidget(lrsGUI);
       stackedWidget->addWidget(coreGUI);

       stackedWidget->setCurrentIndex(0);
       setCentralWidget(stackedWidget);
}

Base::~Base()
{
    qDebug() << "Main Thread: destroying base objects \n";
    delete lrsGUI;
    delete coreGUI;
    delete stackedWidget;
}

void Base::rcvInitData()
{
    qDebug()<< "Main Thread (CALLBACK): Display second screen\n";
    stackedWidget->setCurrentIndex(1);
}

//! [1]
int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    //Instantiate base class    
    Base baseObj;


    //instantiate Client thread object
    ClientThread clientThread;
    qDebug() << "Connecting sendmsg and handle_callback1()\n";
    QObject::connect(&clientThread, SIGNAL(sendInitData()), &baseObj, SLOT(rcvInitData()), Qt::QueuedConnection);

    qDebug() << "Main Thread: starting clockThread\n";
    clientThread.start();

    app.exec();
    qDebug() << "Mian Thread: Quiting clockThread\n";
    clientThread.quit();
    qDebug() << "Main Thread: Waiting on clockThread \n";
    clientThread.wait();
    return 0;
}

To copy to clipboard, switch view to plain text mode 

[d_stranz]

I think we need to start from zero, because something is clearly wrong with what you are doing now.

Please write and run these two programs. You can simply comment out the lines in your current main.cpp and replace them with these lines:

#include <QtWidgets/QApplication>
#include "RaptorCoreGUI.h"
 
int main(int argc, char *argv[])
{
	QApplication a(argc, argv);
 
	RaptorCoreGUI w;
	w.show();
	return a.exec();
}

#include <QtWidgets/QApplication>
#include "RaptorCoreGUI.h"

int main(int argc, char *argv[])
{
	QApplication a(argc, argv);

	RaptorCoreGUI w;
	w.show();
	return a.exec();
}

To copy to clipboard, switch view to plain text mode 

#include <QtWidgets/QApplication>
#include "RaptorLrsGUI.h"
 
int main(int argc, char *argv[])
{
	QApplication a(argc, argv);
 
	RaptorLrsGUI w;
	w.show();
	return a.exec();
}

#include <QtWidgets/QApplication>
#include "RaptorLrsGUI.h"

int main(int argc, char *argv[])
{
	QApplication a(argc, argv);

	RaptorLrsGUI w;
	w.show();
	return a.exec();
}

To copy to clipboard, switch view to plain text mode 

In each case, do you see the windows you expect to see?

[nitks.abhinav]

Yes I can see the windows (attached)

IMG-4835 --> coreGUI
ING-4836 --> lrsGUI

[d_stranz]

OK, good. The problem is not with your Raptor* widgets.

Next step. Do you see the RaptorLrsGUI window when you run this code?

#include <QtWidgets/QApplication>
#include <QtWidgets/QMainWindow>
#include <QtWidgets/QStackedWidget>
#include "RaptorLrsGUI.h"
 
int main(int argc, char *argv[])
{
	QApplication a(argc, argv);
 
	QMainWindow w;
        QStackedWidget * pStack = new QStackedWidget( &w );
        RaptorLrsGUI * pLrs = new RaptorLrsGUI;
        pStack->addWidget( pLrs );
        w.setCentralWidget( pStack );
	w.show();
	return a.exec();
}

#include <QtWidgets/QApplication>
#include <QtWidgets/QMainWindow>
#include <QtWidgets/QStackedWidget>
#include "RaptorLrsGUI.h"

int main(int argc, char *argv[])
{
	QApplication a(argc, argv);

	QMainWindow w;
        QStackedWidget * pStack = new QStackedWidget( &w );
        RaptorLrsGUI * pLrs = new RaptorLrsGUI;
        pStack->addWidget( pLrs );
        w.setCentralWidget( pStack );
	w.show();
	return a.exec();
}

To copy to clipboard, switch view to plain text mode 

If it does, substitute "w.showMaximized()" for "w.show()". Does it still work?