Does splitting widgets into multiple ui forms reduces compilation time?

Daniella

Does splitting widgets into multiple .ui files reduce compilation time? I'm compiling on Visual Studio 2022.

Obviously, I would not add one widget per .ui but complex widgets with a lot of children.

Also, I'm 'including' the new .ui correctly in the code below?

ui_widget.h is a widget.ui created with the Visual Studio option Qt Widgets Form File

// mainwindow.h
#include <QtWidgets/QMainWindow>
#include "ui_MainWindow.h"
#include "ui_widget.h"


class MainWindow: public QMainWindow, public Ui::MainWindowClass
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();

    Ui::MainWindowClass ui;
    Ui::Form form;
     
};

// mainwindow.cpp
#include "stdafx.h"
#include "mainwindow.h"

MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent)
{
    ui.setupUi(this);
    form.setupUi(this); // <- is this correct?

    ui.stackedWidget->insertWidget(0, form.pushButton);
    form.pushButton->show();
}

I asked this same question on StackOverFlow and on comment people suggest something to avoid including the form
using namespace, but i don't understand what they mean.

JonB

@Daniella
Each .ui file produces (via uic) one ui_....h file. And that #includes the Qt headers. So If anything my guess would be that the fewer .ui files you have the faster the compilation, each little extra one may add some overhead!

Not that I would want to take this into account when developing, one monolithic .ui file to save others/cut down on compilation seems a bad approach for development!

You might find in VS that using "precompiled headers" option wherever possible would be best. The ui_....h file is not regenerated unless you change the .ui file, so a lot of the time it would not need to be recompiled?

Daniella

@JonB I see, do you know whats the namespace thing they suggest, to avoid including the .h file?

JoeCFD

The way of using ui file in Qt is from MVC pattern. ui file is the View and can be made by non-programmers(for example artists). If you design ui files by yourself, you may not need ui files at all. But for maintenance purpose, it is better to use ui files since ui might be changed often. I guess compiling time is not an issue here. Not sure how big your project is and ui files will affect compiling time.

jsulm

@Daniella said in Does splitting widgets into multiple ui forms reduces compilation time?:

do you know whats the namespace thing they suggest

I guess they suggest to not to include the ui header file in your widget header file but in the widget cpp file. This is common practise in C++. It also uses forward declaration:

class ui::YOUR_UI_CLASS; // This is forward declaration

class YourWidget
private:
    ui::YOUR_UI_CLASS *ui;

It is always good to use forward declarations for types which are used as pointers. Because then you're including less header files in your header files.

Daniella

What option i should select here? Member pointer?

And then:

// .h
#pragma once
#include <QtWidgets/QMainWindow>

QT_BEGIN_NAMESPACE
namespace Ui { class MainWindowClass; };
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT
public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();

private:
    Ui::MainWindowClass *ui;
};

//.cpp
#include "stdafx.h"
#include "MainWindow.h"
#include "ui_MainWindow.h"

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindowClass())
{
    ui->setupUi(this);
}

This way including ui_MainWindow.h into the .cpp?

JoeCFD

This post is deleted!

jsulm

@Daniella said in Does splitting widgets into multiple ui forms reduces compilation time?:

it didnt compile

Then please post the compiler error.
The code you posted should work.

Daniella

@jsulm I edited my previous answer, is it 'correct' now? whats the advantage of this 'method'?

jsulm

@Daniella said in Does splitting widgets into multiple ui forms reduces compilation time?:

whats the advantage of this 'method'?

I already explained what the advantage is. In short: it reduces compile times. You can also google for "C++ forward declaration".

"What option i should select here?" - member pointer. Forward declarations only work with pointers. For non-pointer members the compiler needs to know the type exactly already in the header file.

Daniella

Thank you, i understand now.
Is possible to modify an existing visual studio project to generate the .ui as member pointer?

jsulm

@Daniella Yes, just edit your code accordingly.

Daniella

@jsulm I'm trying to edit it.

Question, how do i access the ui from others .cpp files than the mainwindow.cpp?

When i try #include mainwindow.h and try ui->centralWidget i get this error:

"pointer to incomplete class type "Ui::MainWindow" is not allowed

Christian Ehrlicher

@Daniella said in Does splitting widgets into multiple ui forms reduces compilation time?:

Question, how do i access the ui from others .cpp files than the mainwindow.cpp?

You must not - write proper functions to access the ui elements.

Daniella

@Christian-Ehrlicher said in Does splitting widgets into multiple ui forms reduces compilation time?:

write proper functions to access the ui elements.

Could you give an example?

// main.cpp
#include "mainwindow.h"

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);    
    MainWindow w;   
    w.show();
}

// mainwindow.h
#include <QtWidgets/QMainWindow>

QT_BEGIN_NAMESPACE
namespace Ui { class MainWindowClass; class Form; };
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT
public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();
    void Test();
    Ui::MainWindowClass *ui;
    Ui::Form *form;
};

// mainwindow.cpp
#include "stdafx.h"
#include "MainWindow.h"
#include "ui_MainWindow.h"
#include "ui_Form.h"

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindowClass())
{
    ui->setupUi(this);
    form->setupUi(this);
}

// test.cpp
#include "mainwindow.h"

void MainWindow::Test()
{ 
     ui->centralWidget; // <-- error: "pointer to incomplete class type "Ui::MainWindowClass" is not allowed
}

how do i access ui in Test()?

SGaist

Hi,

You are missing

#include "ui_MainWindow.h"

in your test.cpp file.

Out of curiosity, why are you creating a new file for that method ? You are making your codebase more complex for no benefit.