path: root/examples/widgets/tutorials/gettingstartedqt.qdoc

// Copyright (C) 2022 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only

/*!
    \example tutorials/notepad
    \title Getting Started Programming with Qt Widgets
    \brief A tutorial for Qt Widgets based notepad application.

    In this topic, we teach basic Qt knowledge by implementing a simple
    Notepad application using C++ and the \l{Qt Widgets} module. The
    application is a small text editor which allows you to create a text
    file, save it, print it,
    or reopen and edit it again. You can also set the font to be used.

    \image notepad1.png "Notepad application"

    \include examples-run.qdocinc

    \section1 Creating the Notepad Project

    Setting up a new project in Qt Creator is aided by a wizard that
    guides you step-by-step through the project creation process. The
    wizard prompts you to enter the settings needed for that particular
    type of project and creates the project for you.

    \note The UI text in Qt Creator and the contents of the generated files
    depend on the Qt Creator version that you use.

    \image notepad2.png "Qt Creator New Project dialog"

    To create the Notepad project, select \uicontrol File >
    \uicontrol {New Project} > \uicontrol {Application (Qt)} >
    \uicontrol {Qt Widgets Application} > \uicontrol Choose, and follow the
    instructions of the wizard. In the \uicontrol{Class Information} dialog,
    type \e Notepad as the class name and select \uicontrol QMainWindow
    as the base class.

    \image notepad3.png "Class Information Dialog"

    The \uicontrol {Qt Widgets Application} wizard creates a project that contains
    a main source file and a set of files that specify a user interface
    (Notepad widget):

    \list
        \li CMakeLists.txt - the project file.
        \li main.cpp - the main source file for the application.
        \li notepad.cpp - the source file of the notepad class of the
            Notepad widget.
        \li notepad.h - the header file of the notepad class for the
            Notepad widget.
        \li notepad.ui - the UI form for the Notepad widget.
    \endlist

    The files come with the necessary boiler plate code for you to be able to
    build and run the project. We will take a closer look at the file contents
    in the following sections.

    \b{Learn More}

    \table
        \header
            \li About
            \li Here
        \row
            \li Using Qt Creator
            \li \l{Qt Creator Manual}{Qt Creator}
        \row
            \li Creating other kind of applications with Qt Creator
            \li \l{Qt Creator: Tutorials}{Qt Creator Tutorials}
    \endtable


    \section1 Main Source File

    The wizard generates the following code in the main.cpp file:

    \quotefromfile tutorials/notepad/main.cpp
    \skipto "notepad.h"
    \printuntil }

    We will go through the code line by line. The following lines include
    the header files for the Notepad widget and QApplication. All Qt classes
    have a header file named after them.

    \quotefromfile tutorials/notepad/main.cpp
    \skipto notepad.h
    \printuntil QApplication

    The following line defines the main function that is the entry point
    for all C and C++  based applications:

    \printline main

    The following line creates a QApplication object. This object manages
    application-wide resources and is necessary to run any Qt program
    that uses Qt Widgets. It constructs an application object with \c argc
    command line arguments run in \c argv. (For GUI applications that
    do not use Qt Widgets, you can use QGuiApplication instead.)

    \skipuntil {
    \printuntil QApplication

    The following line creates the Notepad object. This is the object for
    which the wizard created the class and the UI file. The user interface
    contains visual elements that are called \c widgets in Qt. Examples
    of widgets are text edits, scroll bars, labels, and radio buttons. A
    widget can also be a container for other widgets; a dialog or a main
    application window, for example.

    \printline Notepad

    The following line shows the Notepad widget on the screen in its own
    window. Widgets can also function as containers. An example of this
    is QMainWindow which often contains several types of widgets. Widgets
    are not visible by default; the function \l{QWidget::}{show()} makes
    the widget visible.

    \printline w.show

    The following line makes the QApplication enter its event loop. When
    a Qt application is running, events are generated and sent to the
    widgets of the application. Examples of events are mouse presses
    and key strokes.

    \printline a.exec

    \b{Learn More}

    \table
        \header
            \li About
            \li Here
        \row
            \li Widgets and Window Geometry
            \li \l{Window and Dialog Widgets}
        \row
            \li Events and event handling
            \li \l{The Event System}
    \endtable

    \section1 Designing a UI

    The wizard generates a user interface definition in XML format: notepad.ui.
    When you open the notepad.ui file in Qt Creator, it automatically
    opens in the integrated Qt Designer.

    When you build the application, Qt Creator launches the Qt
    \l{User Interface Compiler (uic)} that reads the .ui file and creates
    a corresponding C++ header file, ui_notepad.h.

    \section2 Using Qt Designer

    The wizard creates an application that uses a QMainWindow. It has
    its own layout to which you can add a menu bar, dock widgets, toolbars,
    and a status bar. The center area can be occupied by any kind of widget.
    The wizard places the Notepad widget there.

    To add widgets in Qt Designer:

    \list 1
        \li In the Qt Creator \uicontrol Edit mode, double-click the notepad.ui
            file in the \uicontrol Projects view to launch the file in the integrated
            Qt Designer.
        \li Drag and drop widgets Text Edit (QTextEdit) to the form.
        \li Press \key {Ctrl+A} (or \key {Cmd+A}) to select the widgets and click
            \uicontrol {Lay out Vertically} (or press \key {Ctrl+L}) to apply a vertical
            layout (QVBoxLayout).
        \li Press \key {Ctrl+S} (or \key {Cmd+S}) to save your changes.
    \endlist

    The UI now looks as follows in Qt Designer:

    \image notepad4.png

    You can view the generated XML file in the code editor:

    \quotefromfile tutorials/notepad/notepad.ui

    \printuntil QMenuBar
    \dots

    The following line contains the XML declaration, which specifies the
    XML version and character encoding used in the document:

    \code
    <?xml version="1.0" encoding="UTF-8"?>
    \endcode

    The rest of the file specifies an \c ui element that defines a
    Notepad widget:

    \code
    <ui version="4.0">
    \endcode

    The UI file is used together with the header and source file of the
    Notepad class. We will look at the rest of the UI file in the later
    sections.

    \section2 Notepad Header File

    The wizard generated a header file for the Notepad class that has the
    necessary #includes, a constructor, a destructor, and the Ui object.
    The file looks as follows:

    \quotefromfile tutorials/notepad/notepad.h
    \skipto #include
    \printuntil ~Notepad();
    \skipto private:
    \printuntil };

    The following line includes QMainWindow that provides a main application
    window:

    \quotefromfile tutorials/notepad/notepad.h
    \skipto #include
    \printuntil >

    The following lines declare the Notepad class in the Ui namespace,
    which is the standard namespace for the UI classes generated from
    .ui files by the \c uic tool:

    \skipto Ui {
    \printuntil }

    The class declaration contains the \c Q_OBJECT macro. It must come
    first in the class definition, and declares our class as a QObject.
    Naturally, it must also inherit from QObject. A QObject adds several
    abilities to a normal C++ class. Notably, the class name and slot
    names can be queried at runtime. It is also possible to query a slot's
    parameter types and invoke it.

    \skipto class Notepad
    \printuntil Q_OBJECT

    The following lines declare a constructor that has a default argument
    called \c parent.
    The value 0 indicates that the widget has no parent (it is a top-level
    widget).

    \printuntil explicit

    The following line declares a virtual destructor to free the resources
    that were acquired by the object during its life-cycle. According to
    the C++ naming convention, destructors have the same name as the class
    they are associated with, prefixed with a tilde (~). In QObject,
    destructors are virtual to ensure that the destructors of derived
    classes are invoked properly when an object is deleted through a
    pointer-to-base-class.

    \printuntil ~Notepad();

    The following lines declare a member variable which is a pointer to
    the Notepad UI class. A member variable is associated with a specific
    class, and accessible for all its methods.

    \skipto private:
    \printuntil };

    \section2 Notepad Source File

    The source file that the wizard generated for the Notepad class looks
    as follows:

    \quotefromfile tutorials/notepad/notepad.cpp
    \skipto #include "notepad.h"
    \printuntil  ui->setupUi(this);
    \skipto }
    \printuntil }

    The following lines include the Notepad class header file that was
    generated by the wizard and the UI header file that was generated
    by the \c uic tool:

    \quotefromfile tutorials/notepad/notepad.cpp
    \skipto #include "notepad.h"
    \printuntil #include "ui_notepad.h"

    The following line  defines the \c {Notepad} constructor:

    \printuntil Notepad::Notepad

    The following line  calls the QMainWindow constructor, which is
    the base class for the Notepad class:

    \printuntil QMainWindow

    The following line  creates the UI class instance and assigns it to
    the \c ui member:

    \printline ui(new

    The following line sets up the UI:

    \printuntil ui->setupUi(this)

    In the destructor, we delete the \c ui:

    \skipto Notepad::~Notepad
    \printuntil }

    \section2 Project File

    The wizard generates the following project file, \c CMakeLists.txt, for
    us:

    \quotefile tutorials/notepad/CMakeLists.txt

    The project file specifies the source, header, and UI files included in
    the project.

    \b{Learn More}

    \table
        \header
            \li About
            \li Here
        \row
            \li Using Qt Designer
            \li \l{Qt Designer Manual}
        \row
            \li Layouts
            \li \l{Layout Management},
               \l{Widgets and Layouts},
               \l{Layout Examples}
        \row
            \li The widgets that come with Qt
            \li \l{Qt Widget Gallery}
        \row
            \li Main windows and main window classes
            \li \l{Application Main Window},
               \l{Main Window Examples}
        \row
            \li QObjects and the Qt Object model (This is essential to
                understand Qt)
            \li \l{Object Model}
        \row
            \li qmake and the Qt build system
            \li \l{qmake Manual}
    \endtable

    \section1 Adding User Interaction


    To add functionality to the editor, we start by adding menu items
    and buttons on a toolbar.

    Click on "Type Here", and add the options New, Open, Save, Save as,
    Print and Exit. This creates 5 lines in the Action Editor below.
    To connect the actions to slots, right-click an action and select
    \uicontrol {Go to slot} > \uicontrol triggered(), and complete the
    code for that given slot.

    If we also want to add the actions to a toolbar, we can assign an
    icon to each QAction, and then drag the QAction to the toolbar. You
    assign an icon by entering an icon name in the Icon property of the
    action concerned. When the QAction has been dragged to the toolbar,
    clicking the icon will launch the associated slot.

    Complete the method \c newDocument():

    \quotefromfile tutorials/notepad/notepad.cpp
    \skipto newDocument()
    \printuntil }

    The \c currentFile variable is a global variable containing the file
    presently being edited, and \c clear() clears the text buffer.
    The \c currentFile variable is defined in the private part of notepad.h:

    \quotefromfile tutorials/notepad/notepad.h
    \skipto private:
    \printuntil currentFile;

    \section2 Opening a file

    In \c notepad.ui, right click on \c actionOpen and select
    \uicontrol {Go to Slot}.

    Complete method \c open().

    \quotefromfile tutorials/notepad/notepad.cpp
    \skipto open()
    \printuntil file.close
    \printuntil }


    \c QFileDialog::getOpenFileName opens a dialog enabling you to select
    a file. QFile object \c myfile has the selected \c file_name as
    parameter. We store the selected file also into the global variable
    \c currentFile for later purposes. We open the file with \c file.open
    as a readonly text file. If it cannot be opened, a warning is issued,
    and the program stops.

    We define a QTextStream \c instream for parameter \c myfile.
    The contents of file \c myfile is copied into QString \c text.
    \c setText(text) fills the buffer of our editor with \c text.

    \section2 Saving a file

    We create the method for saving a file in the same way as for
    \l {Opening a file}, by right clicking on \c actionSave, and
    selecting \uicontrol {Go to Slot}.

    \skipto Notepad::save
    \printuntil file.close
    \printuntil }

    QFile object \c myfile is linked to global variable \c current_file,
    the variable that contains the file we were working with.
    If we cannot open \c myfile, an error message is issued and the
    method stops. We create a QTextStream \c outstream. The contents
    of the editor buffer is converted to plain text, and then written
    to \c outstream.

    \section2 Saving a file under another name

    \skipto Notepad::saveAs
    \printuntil file.close
    \printuntil }

    This is the same procedure as for \l {Saving a file}, the only
    difference being that here you need to enter a new file name for
    the file to be created.


    \section2 Printing a File

    If you want to use print functionalities, you need to add
    \c PrintSupport to the project file:

    \quotefromfile tutorials/notepad/CMakeLists.txt
    \skipto find_package(Qt6
    \printuntil )

    In \c notepad.cpp, we declare a QPrinter object called \c printDev:

    \quotefromfile tutorials/notepad/notepad.cpp
    \skipto void Notepad::print()
    \printuntil }

    We launch a printer dialog box and store the selected printer in
    object \c printDev. If we clicked on \c Cancel and did not select
    a printer, the methods returns. The actual printer command is given
    with \c ui->textEdit->print with our QPrinter object as parameter.

    \section2 Select a Font

    \skipto Notepad::selectFont
    \printuntil }

    We declare a boolean indicating if we did select a font with
    QFontDialog. If so, we set the font with \c ui->textEdit->setFont(myfont).

    \section2 Copy, Cut, Paste, Undo, and Redo

    If you select some text, and want to copy it to the clipboard,
    you call the appropriate method of \c ui->textEdit. The same counts
    for cut, paste, undo, and redo.

    This table shows the method name to use.

    \table
    \header
        \li Task
        \li Method called
    \row
        \li Copy
        \li ui->textEdit->copy()
    \row
        \li Cut
        \li ui->textEdit->cut()
    \row
        \li Paste
        \li ui->textEdit->paste()
    \row
        \li Undo
        \li ui->textEdit->undo()
    \row
        \li Redo
        \li ui->textEdit->redo()
    \endtable

    \b{Learn More}

    \table
        \header
            \li About
            \li Here
        \row
            \li MDI applications
            \li QMdiArea,
               \l{MDI Example}
        \row
            \li Files and I/O devices
            \li QFile, QIODevice
        \row
            \li tr() and internationalization
            \li \l{Qt Linguist Manual},
               \l{Writing Source Code for Translation},
               \l{Internationalization with Qt}
    \endtable

    \include cli-build-cmake.qdocinc cli-build-cmake
*/