Using Stacked Widgets

[Juan de Dironne]

I recently created a Post about an application that I have to make with many interfaces.
As the number of interfaces is important I decided to separate my files (cpp and h) according to the interfaces.

I had opted for a solution that was not ideal and @jsulm and @JonB therefore advised me to use "Stacked Widgets".
So I searched and found some information, but very few refer to "Stacked Widgets" and a "Menu" (in a Main Window).
But I finally managed to create a project with what I need.

But is it correct...?
Is the structure with file separation correct...?
And if so, how could I modify a member present in my main window from an interface...? (example with "stringTest")

main.cpp

#include<QApplication>
#include"MyMainWindow.h"

int main(int nbArg, char* listeArg[])
{
  QApplication myApp(nbArg,listeArg);

  MyMainWindow myWindow;
  myWindow.show();

  myApp.exec();
}

MyMainWindow.cpp

#include"MyMainWindow.h"

MyMainWindow::MyMainWindow()
{
  setWindowTitle("Stacked Widgets");
  setMinimumHeight(600);
  setMinimumWidth(600);

  m_actionQuit = new QAction("Quit",this);
  m_actionInterfaceA = new QAction("Interface A",this);
  m_actionInterfaceB = new QAction("Interface B",this);
  m_actionInterfaceC = new QAction("Interface C",this);

  m_menuFile = menuBar()->addMenu("File");
  m_menuFile->addAction(m_actionInterfaceA);
  m_menuFile->addAction(m_actionInterfaceB);
  m_menuFile->addAction(m_actionInterfaceC);
  m_menuFile->addAction(m_actionQuit);

  // Definition of Widget Central
  centralZone = new QWidget;

  // Definitions of the Different Widgets
  widgetHome        = new Home;               widgetHome->setObjectName("home");
  widgetInterfaceA  = new InterfaceA;         widgetInterfaceA->setObjectName("interfaceA");
  widgetInterfaceB  = new InterfaceB;         widgetInterfaceB->setObjectName("interfaceB");
  widgetInterfaceC  = new InterfaceC;         widgetInterfaceC->setObjectName("interfaceC");

  // Definition of Stacked Widget
  m_stackedWidget = new QStackedWidget(centralZone);
  m_stackedWidget->setMinimumHeight(minimumHeight());
  m_stackedWidget->setMinimumWidth(minimumWidth());
  m_stackedWidget->addWidget(widgetHome);
  m_stackedWidget->addWidget(widgetInterfaceA);
  m_stackedWidget->addWidget(widgetInterfaceB);
  m_stackedWidget->addWidget(widgetInterfaceC);

  // Creation Layout and Placement
  QVBoxLayout *layoutCentralZone = new QVBoxLayout;
  centralZone->setLayout(layoutCentralZone);
  setCentralWidget(centralZone);

  // Creation Connection Signal / Slot
  connect(m_actionQuit,SIGNAL(triggered(bool)),qApp,SLOT(quit()));
  connect(m_actionInterfaceA,SIGNAL(triggered(bool)),this,SLOT(showInterfaceA()));
  connect(m_actionInterfaceB,SIGNAL(triggered(bool)),this,SLOT(showInterfaceB()));
  connect(m_actionInterfaceC,SIGNAL(triggered(bool)),this,SLOT(showInterfaceC()));
}



void MyMainWindow::showInterfaceA(){  m_stackedWidget->setCurrentIndex(m_stackedWidget->indexOf(widgetInterfaceA)); }

void MyMainWindow::showInterfaceB() { m_stackedWidget->setCurrentIndex(m_stackedWidget->indexOf(widgetInterfaceB)); }

void MyMainWindow::showInterfaceC() { m_stackedWidget->setCurrentIndex(m_stackedWidget->indexOf(widgetInterfaceC)); }

MyMainWindow.h

#ifndef MYMAINWINDOW_H
#define MYMAINWINDOW_H

#include<QtWidgets>
#include"Home.h"
#include"InterfaceA.h"
#include"InterfaceB.h"
#include"InterfaceC.h"

class MyMainWindow : public QMainWindow
{
  Q_OBJECT

  public:
  MyMainWindow();
  QString m_stringTest = "ABCDEF";

  public slots:
  void showInterfaceA();
  void showInterfaceB();
  void showInterfaceC();

  private:
  QMenu *m_menuFile;
  QAction *m_actionInterfaceA;
  QAction *m_actionInterfaceB;
  QAction *m_actionInterfaceC;
  QAction *m_actionQuit;

  QWidget *centralZone;

  QStackedWidget *m_stackedWidget;
  Home *widgetHome;
  InterfaceA *widgetInterfaceA;
  InterfaceB *widgetInterfaceB;
  InterfaceC *widgetInterfaceC;
};

#endif // MYMAINWINDOW_H

Home.cpp

#include"Home.h"

Home::Home()
{
  // Initialization
  QGridLayout *layoutPage;    layoutPage    = new QGridLayout();          layoutPage->setAlignment(Qt::AlignCenter);

  layoutPage->addWidget(new QLabel("Accueil"));

  // Definition of the "Layout" of the "Widget"
  setLayout(layoutPage);
}

Home.h

#ifndef HOME_H
#define HOME_H

#include<QtWidgets>

class Home : public QWidget
{
  public:
  Home();

  private:
};

#endif // HOME_H

InterfaceA.cpp

#include"InterfaceA.h"

InterfaceA::InterfaceA()
{
  // Initialization
  QGridLayout *layoutPage;    layoutPage    = new QGridLayout();          layoutPage->setAlignment(Qt::AlignCenter);

  layoutPage->addWidget(new QLabel("Interface A"));

  // Definition of the "Layout" of the "Widget"
  setLayout(layoutPage);
}

InterfaceA.h

#ifndef INTERFACEA_H
#define INTERFACEA_H

#include<QtWidgets>

class InterfaceA : public QWidget
{
  public:
  InterfaceA();

  private:
};

#endif // INTERFACEA_H

The complete example is visible on gitHub at this adress :
https://github.com/JuanDeDironne/qt_example_stacked_widgets

[JonB]

@Juan-de-Dironne
Looks like reasonable QStackedWidget usage to me.

And if so, how could I modify a member present in my main window from an interface...? (example with "stringTest")

Don't know what this means.

void MyMainWindow::showInterfaceA(){ m_stackedWidget->setCurrentIndex(m_stackedWidget->indexOf(widgetInterfaceA)); }

You can simplify this, since QStackedWidget offers

 m_stackedWidget->setCurrentWidget(widgetInterfaceA);

connect(m_actionQuit,SIGNAL(triggered(bool)),qApp,SLOT(quit()));

Old style connect()s with SIGNAL/SLOT macros were deprecated a decade ago. Please change over to:

connect(m_actionQuit, &QAction::triggered, qApp, &QApplication::quit);

[Juan de Dironne]

@JonB
Thanks a lot for your answers.
For the old style of connection, I confess that I find out.

And when I say "And if so, how could I modify a member present in my main window from an interface...? (example with "stringTest")".
This means that my "Interface A", for example, could retrieve input data that I would like to store in a variable of my "MainWindow" Class.
So that this variable is, for example, used on other Interfaces.

[JonB]

@Juan-de-Dironne said in Using Stacked Widgets:

This means that my "Interface A", for example, could retrieve input data that I would like to store in a variable of my "MainWindow" Class.

If the "interface" classes are modal dialogs you could return whatever was entered after QDialog::exec() to be stored in MainWindow. If they are modeless widgets (as you show) then I would probably write a signal which they emit with a parameter of the data, and have a slot in MainWindow forward the data to other interface widgets if required. Or possibly save it in some "shared" application/UI object (e.g. perhaps a model) which all interfaces can see. What I would not do is have something which allows the interface widgets to make direct calls into the MainWindow class.

[Juan de Dironne]

@JonB Thanks again for your reply.
You had already mentioned the "signals/slots" solution to communicate between the different classes in my Previous Post.
So I have to look into this solution.
But you mention the possibility of a shared object...? I don't see how to set this up...?
It would be a class...? Inherited from QOject...? But if so, how do you share it...?
I admit I don't know how to implement this solution.

[jsulm]

@Juan-de-Dironne said in Using Stacked Widgets:

It would be a class...? Inherited from QOject...? But if so, how do you share it...?

What ever you want to share. It can be a variable of some basic type or an instance of a struct/class. To share it you simply pass a pointer or reference to this object to all objects which needs to use it:

struct MyData
{
...
};

MyData data;
MyClass myClass(&data);
MyClass myClass2(&data);

[Juan de Dironne]

@jsulm Thanks for your time and reply
So in my case I can create a structure like this :
MySharedStructure.h

struct MySharedStructure
{
  QString myString = "123";
};

That I instantiate in "MyMainWindow.cpp" and pass a pointer to the constructor of my "InterfaceA" like this :

MyMainWindow.cpp

#include"MyMainWindow.h"
#include"MySharedStructure.h"

MyMainWindow::MyMainWindow()
{
  setWindowTitle("Stacked Widgets");
  setMinimumHeight(600);
  setMinimumWidth(600);

  MySharedStructure myData;
...
...
  // Definitions of the Different Widgets
  widgetHome        = new Home;                 widgetHome->setObjectName("home");
  widgetInterfaceA  = new InterfaceA(&myData);  widgetInterfaceA->setObjectName("interfaceA");
...
...

InterfaceA.h

#include<QtWidgets>
#include"MySharedStructure.h"

class InterfaceA : public QWidget
{
  Q_OBJECT

  public:
  InterfaceA(MySharedStructure*);
}

With all this code in my constructor of my InterfaceA I can display if I want my character string stored in my structure like this :
InterfaceA.cpp

#include"InterfaceA.h"

InterfaceA::InterfaceA(MySharedStructure* dataFonc)
{
  qDebug() << dataFonc->myString;
}

In principle, this is how I should set things up to have a shared structure (in this case)...?

[mpergand]

@Juan-de-Dironne
Hi,
One of the OOP principles is to only give each object the food they need :)

So you can give your data a more structured form, like that:

struct Interface1Data
    {
    int i=1;
    };

struct Interface2Data
    {
    int i=2;
    };

struct AllData
{
    int i=0;    // global
    Interface1Data data1;
    Interface2Data data2;
};

class Interface1
{
    public:
        Interface1(Interface1Data* d) : data(d)
        {
            qDebug()<<Q_FUNC_INFO<<data->i;
        }

    private:
        Interface1Data* data;
};

class Interface2
{
    public:
        Interface2(Interface2Data* d) : data(d)
        {
            qDebug()<<Q_FUNC_INFO<<data->i;
        }

    private:
        Interface2Data* data;
};

int main(int argc, char *argv[])
{
    AllData data;
    qDebug()<<data.i<<data.data1.i<<data.data2.i;
    Interface1 i1(&data.data1);
    Interface2 i2(&data.data2);
    return 0;

This way each interface deals with its own data and can't corrupt other interface ones.

[Juan de Dironne]

@mpergand
Whaouh
At first my brain made knots when I read your code.
Once your code understood (which works perfectly) I adapted it to separate the classes in file.
And it gives that.
main.cpp

AllData.h

Interface1

I made screenshots because I think it's easier to show the structure of the project that I put in place.
And before going further, is this project structure correct by applying your principle...?

[mpergand]

@Juan-de-Dironne
Seems OK.

I presume you want to save/load the all data structure, it's time to think about it ;)

[Juan de Dironne]

@mpergand
Thank you again for your answers and the time spent :)
And "to save/load the all data structure". That's to say...?

Because I actually have a question. I have shared data but basically my "Interfaces" files should allow me to separate each Graphical Interface (each Stacked Widget).
And let's imagine that my "Interface 1" is a page with input of information and validation of it.
How could I save this information in my "AllData" structure so that it can be shared later...?
Hope to be clear in my explanations.

[mpergand]

@Juan-de-Dironne said in Using Stacked Widgets:

How could I save this information in my "AllData" structure so that it can be shared later...?

Currently each interface receives a pointer to the data, not a copy, that means:
Interface1Data* data
points to allData.data1
(same addresses)

so in interface1
data->i=xx
is the same as
allData.data1.i=xx

[Juan de Dironne]

@mpergand
I'm trying to understand what you're explaining.
And if I understood correctly, you are telling me that I can access all the data present in my "Interface" classes from my "allData" class.
But in principle, I would like from my interface to be able to update "global" data.
And with this principle I do not see how to do it in fact.

[jsulm]

@Juan-de-Dironne said in Using Stacked Widgets:

I would like from my interface to be able to update "global" data

"global data" is bad design.
But if you pass pointer to your "global data" like @mpergand wrote you can modify this global data because you're not passing copies of the global data, but pointer to it. So, don't know what the problem is...

[Juan de Dironne]

@jsulm
In fact the principle is not to set up "global" data which could be accessible and shared between several interfaces...? Because...?
This concept is not good...?

Because that's what I had actually envisioned.
An interface (interface 1) allowed me for example to display a connection screen and manage the identification.
Once logged in the "User ID" was stored in a "global structure".
This ID could be used by another interface (interface 2, interface 3, ...)

But with pointer passing, we can access data from different interfaces. But no shared data in fact..? But no global data...?

[jsulm]

@Juan-de-Dironne said in Using Stacked Widgets:

But no shared data in fact..?

What do you mean? If you pass pointer to some variable to different parts of your code then you're sharing this variable.

"Once logged in the "User ID" was stored in a "global structure"." - can you explain what exactly you mean if you write "global data"?

There should not be global data in a properly designed application. There should be clear ownership for each piece of data. For example your user id should be stored in some class which then provides it to whoever needs it.

[Juan de Dironne]

Thank you all for your past and your answers. Indeed I learned through your answers to set up a sharing of data and especially to understand how to organize the data and divide them well into classes. Thank you again :) After... It's not won, I have to get used to this gymnastics of the mind but I have grasped the principle.