<< qt

Qt

This document shows the very fundamental concepts about Qt.

1. Compile Qt Program

Three approaches to compling the Qt Program introduced: manually, CMake, and QMake.

# Manually g++

==TODO: Find out how to build Qt program manually with clang==. Notice that this approach might be difficult since the Qt provides cmake files in the library, which is not usable for the complier itself.

# CMake Approach

# QMake Approach

Similar to cmake, Qt provides qmake to generate makefile automatically. The extension of description file for qmake is .pro. The basic hello.pro demo is

QT += widgets
SOURCES = hello.cpp
TARGET = hello

Use qmake -o Makefile hello.pro to generate the Makefile.

• In macOS, make will generate a macOS Application bundle(.app directory), (and an object file as the byproduct), where contains the Mach-O 64-bit executable file in ./Contents/MacOS.
• ==TODO: Linux Behaviour.==
• ==TODO: Windows Behaviour.==

Further knowledge about qmake and pro file will be introduced in qmake.

2. Program Demo

Demonstrate the minimal Qt Programs to show how the baisc structure.

# Minimal Qt Program

The minimal program of Qt

#include <QApplication>

int main(int argc, char **argv) {
    QApplication app (argc, argv);
    return app.exec();
}

The QApplication object takes the input arguments and launches event loop by invoking app.exec() method. Since no window or event handler is created, the program will just run the infinite loop without any windows and responding.

# Minimal Widget

The component of Qt’s graphic interface is widget. This reflects in the class hierarchy, where all the window objects are inherited from QWidget directly or indirectly. For example, the QPushButton class inherits QAbstractButton and the latter one inherits QWidget.

classDiagram
     QObject <|-- QWidget
     QWidget <|-- QAbstractButton
     QAbstractButton <|-- QPushButton
     QWidget <|-- QComboBox
     QWidget <|-- QMenu

#include <QApplication>
#include <QPushButton>

int main(int argc, char **argv){
    QApplication app(argc, argv);
    QPushButton button("Hello world !");
    button.show();
    return app.exec();
}

We instantiate the QtWidget QPushButton and show() it, each widget is placed in the indepndent header, as this example shown.

3. Utility Widget

# QWidget

The windows itself is also a widget, named as QWidget.

#include <QApplication>
#include <QWidget>

int main (int argc, char* argv[]) {
    QApplication app(argc, argv);
    QWidget window;

    window.resize(250, 150);
    window.move(300, 300);
    window.setWindowTitle("Simple example");
    window.setToolTip("QWidget");
    window.show();

    return app.exec();
}

Most of the functions of method are self-explain by their names. No further illustration necessary.