UI (New ui:: MainWindow) troubleshooting

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One 、 Problem description

QT Generate a simple MainWindow After the project ,mainwindows.cpp in , Realized MainWindow Constructor for , See the following code .

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

Two lines of code after the colon , yes C++ List initialization of . among QMainWindow(parent) Is to explicitly call the constructor of the base class , ui(new Ui::MainWindow) Is initialization ui The pointer .ui Pointer in mainwindow.h As defined in .

I saw ui(new Ui::MainWindow) , Here comes my question ,MainWindow Constructor for , Meeting new One MainWindow, No, I will call again MainWindow Constructor of ？ This is not a set of dolls ？ It's going to cycle . But the actual operation is normal , It must be my own misunderstanding .

Conclusion ：
QT Name two different classes MainWindow, adopt namespace It makes a distinction .
Ui Variable name of namespace , And the variable name of the default space , Although the same , But there are actually two things .

Two 、 Problem analysis

1.mainwindow.h

See the notes of the code

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

namespace Ui {
    
class MainWindow_gui; //  The original MainWindow Change it to MainWindow_gui.  Here in “Ui” In the namespace of , Declared a MainWindow_gui class .
}

class MainWindow : public QMainWindow // MainWindow  Is based on QMainWindow  Derived classes 
{
    
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

private:
     //  Defined a point MainWindow_gui The pointer to pui.MainWindow_gui Is in Ui In namespace , So write it as “ Ui::MainWindow_gui”
     Ui::MainWindow_gui * pui;
};

#endif // MAINWINDOW_H

2.ui_mainwindow.h

This file , Not under the project directory , Should be qt After generation, it is placed in the compilation directory . Compile time will connect .
See the notes of the code

#ifndef UI_MAINWINDOW_H
#define UI_MAINWINDOW_H

#include <QtCore/QVariant>
// *** Omit ***

class Ui_MainWindow //  Defined a  Ui_MainWindow  class 
{
    
public:
	// *** Omit ***
    void setupUi(QMainWindow *MainWindow)
    {
    
		// *** Omit ***
    } // setupUi
};

namespace Ui {
    
	// Ui In space , Defined a MainWindow_gui class , This class inherits from Ui_MainWindow 
    class MainWindow_gui: public Ui_MainWindow {
    }; 
} // namespace Ui
#endif // UI_MAINWINDOW_H

3.mainwindow.cpp

This file , Not under the project directory , Should be qt After generation, it is placed in the compilation directory . Compile time will connect .
See the notes of the code

//  Manual test , There is no order between the two header files include The relationship between 
#include "mainwindow.h" 
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent) : //  The concrete realization of MainWindow Constructor for 
    QMainWindow(parent),  //  Call the base class QMainWindow Constructor for , because MainWindow It's from QMainWindow Derived from 
    pui(new Ui::MainWindow_gui) // new One Ui In space MainWindow_gui class , And initialize its pointer pui
{
    
    pui->setupUi(this);
}
MainWindow::~MainWindow()
{
    
    delete pui;
}