Analysis of file dependence of Qt in creating Application

When using QtCreator to create Application program, it will automatically create * * *. UI file in the folder "build - * * * - Desktop"_ Qt_ ***-Generate UI in debug_ ***. h, * * *. UI can be adjusted through QtDesigner, and a c + + class with the same name will be created in the folder of * * *. UI. This brings us a lot of doubts. How does QT generate UI? Here we do a simple analysis.

mainwindow.ui File:

<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
 <class>MainWindow</class>
 <widget class="QMainWindow" name="MainWindow">
  <property name="geometry">
   <rect>
    <x>0</x>
    <y>0</y>
    <width>800</width>
    <height>600</height>
   </rect>
  </property>
  <property name="windowTitle">
   <string>MainWindow</string>
  </property>
  <widget class="QWidget" name="centralwidget"/>
  <widget class="QMenuBar" name="menubar">
   <property name="geometry">
    <rect>
     <x>0</x>
     <y>0</y>
     <width>800</width>
     <height>23</height>
    </rect>
   </property>
  </widget>
  <widget class="QStatusBar" name="statusbar"/>
 </widget>
 <resources/>
 <connections/>
</ui>

Auto generated ui_mainwindow.h file:

/********************************************************************************
** Form generated from reading UI file 'mainwindow.ui'
**
** Created by: Qt User Interface Compiler version 5.12.8
**
** WARNING! All changes made in this file will be lost when recompiling UI file!
********************************************************************************/

#ifndef UI_MAINWINDOW_H
#define UI_MAINWINDOW_H

#include <QtCore/QVariant>
#include <QtWidgets/QApplication>
#include <QtWidgets/QMainWindow>
#include <QtWidgets/QMenuBar>
#include <QtWidgets/QStatusBar>
#include <QtWidgets/QWidget>

QT_BEGIN_NAMESPACE

class Ui_MainWindow
{
public:
    QWidget *centralwidget;
    QMenuBar *menubar;
    QStatusBar *statusbar;

    void setupUi(QMainWindow *MainWindow)
    {
        if (MainWindow->objectName().isEmpty())
            MainWindow->setObjectName(QString::fromUtf8("MainWindow"));
        MainWindow->resize(800, 600);
        centralwidget = new QWidget(MainWindow);
        centralwidget->setObjectName(QString::fromUtf8("centralwidget"));
        MainWindow->setCentralWidget(centralwidget);
        menubar = new QMenuBar(MainWindow);
        menubar->setObjectName(QString::fromUtf8("menubar"));
        menubar->setGeometry(QRect(0, 0, 800, 23));
        MainWindow->setMenuBar(menubar);
        statusbar = new QStatusBar(MainWindow);
        statusbar->setObjectName(QString::fromUtf8("statusbar"));
        MainWindow->setStatusBar(statusbar);

        retranslateUi(MainWindow);

        QMetaObject::connectSlotsByName(MainWindow);
    } // setupUi

    void retranslateUi(QMainWindow *MainWindow)
    {
        MainWindow->setWindowTitle(QApplication::translate("MainWindow", "MainWindow", nullptr));
    } // retranslateUi

};

namespace Ui {
    class MainWindow: public Ui_MainWindow {};
} // namespace Ui

QT_END_NAMESPACE

#endif // UI_MAINWINDOW_H

Here, we can see that there is UI in the file_ MainWindow class, but this class does not inherit from Qt class, so the displayed form is not Ui_MainWindow, but it contains the UI controls, and there is a void setupUi(QMainWindow *MainWindow) method. The parameter passed in by this method is a Qt UI class, and the UI class passed in is UI_ Controls in MainWindow. Finally, define inheritance UI in namespace Ui_MainWindow class of MainWindow.

In the automatically generated c + + class, the h/cpp file is as follows:

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QAction>

QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT

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



private:
    Ui::MainWindow *ui;

    // QAction is added by myself
    QAction* new_action_;
    QAction* exit_action_;
};
#endif // MAINWINDOW_H
#include <QAction>

#include "mainwindow.h"
#include "ui_mainwindow.h"

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

    new_action_ = new QAction(tr("&New"), this);
    new_action_->setShortcut(QKeySequence::New);

    exit_action_ = new QAction(tr("E&xit"), this);
    exit_action_->setShortcut(QKeySequence::Quit);

    menuBar()->addAction(new_action_);
}

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

We can see that MainWindow inherits QMainWindow, and MainWindow has a private variable Ui::MainWindow *ui (the Ui space mentioned above inherits Ui_MainWindow class of MainWindow), in the constructor Ui - > setupui (this).

 

Conclusion:

  1. The UI displayed after the program is actually the MainWindow in the c++ file.
  2. The controls in MainWindow use UI - > setupui (this) to set UI_ In the MainWindow class, assign MainWindow.
  3. Ui_MainWindow and UI files are actually just control libraries and layout frameworks, and do not really display the UI.

Tags: Programming Qt xml encoding

Posted on Sat, 30 May 2020 21:40:07 -0700 by andy1398