// 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 \examplecategory {User Interface Components} \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 \endcode The rest of the file specifies an \c ui element that defines a Notepad widget: \code \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 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 */