path: root/doc/src/getting-started/gettingstartedqt.qdoc

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/*!
    \page gettingstartedqt.html

    \title Getting Started Programming with Qt Widgets

    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"

    You can find the final Notepad source files in the qtdoc repository in the
    snippets/widgets-tutorial/notepad directory. You can either fetch
    the Qt 5 sources from Qt Project or install them as part of Qt 5.

    \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.

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

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

    \image notepad3.png "Class Information Dialog"

    The \b {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 notepad.pro - 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 .cpp, .h, and .ui files come with the necessary boiler plate code for
    you to be able to build and run the project. The .pro file is complete.
    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:

    \snippet snippets/widgets-tutorial/notepad/main.cpp all

    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.

    \snippet snippets/widgets-tutorial/notepad/main.cpp 1

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

    \snippet snippets/widgets-tutorial/notepad/main.cpp 2

    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.)

    \snippet snippets/widgets-tutorial/notepad/main.cpp 3

    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.

    \snippet snippets/widgets-tutorial/notepad/main.cpp 4

    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.

    \snippet snippets/widgets-tutorial/notepad/main.cpp 5

    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.

    \snippet snippets/widgets-tutorial/notepad/main.cpp 6

    \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 \b Editor mode, double-click the notepad.ui file
            in the \b Projects view to launch the file in the integrated Qt
            Designer.
        \li Drag and drop widgets Text Edit (QTextEdit) to the form.
        \li Press \b {Ctrl+A} (or \b {Cmd+A}) to select the widgets and click
            \b {Lay out Vertically} (or press \b {Ctrl+L}) to apply a vertical
            layout (QVBoxLayout).
        \li Press \b {Ctrl+S} (or \b {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 snippets/widgets-tutorial/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:

    \snippet snippets/gs/notepad1.h all

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

    \snippet snippets/gs/notepad1.h 1

    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:

    \snippet snippets/gs/notepad1.h 2

    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.

    \snippet snippets/gs/notepad1.h 3

    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).

    \snippet snippets/gs/notepad1.h 4

    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.

    \snippet snippets/gs/notepad1.h 5

    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.

    \snippet snippets/gs/notepad1.h 6

    \section2 Notepad Source File

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

    \snippet snippets/gs/notepad1.cpp all

    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:

    \snippet snippets/gs/notepad1.cpp 0

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

    \snippet snippets/gs/notepad1.cpp 1

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

    \snippet snippets/gs/notepad1.cpp 2

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

    \snippet snippets/gs/notepad1.cpp 3

    The following line  sets up the UI:

    \snippet snippets/gs/notepad1.cpp 4

    In the destructor, we delete the \c ui:

    \snippet snippets/gs/notepad1.cpp 5

    In order to have the text edit field occupy the whole screen, we add
    \c setCentralWidget to the main window.

    \snippet snippets/widgets-tutorial/notepad/notepad.cpp 1

    \section2 Project File

    The wizard generates the following project file, \c {notepad.pro}, for us:

    \quotefile snippets/widgets-tutorial/notepad/notepad.pro

    The project file specifies the application name and the \c qmake template to
    use for generating the project, as well as the source, header, and UI files
    included in the project.

    You could also use \c qmake's \c -project option to generate the \.pro file. Although,
    in that case, you have to remember to add the line \c{QT += widgets} to the generated
    file in order to link against the Qt Widgets Module.

    \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 Go to slot > 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 on_actionNew_triggered() :

    \snippet snippets/widgets-tutorial/notepad/notepad.cpp 2

    \c current_file is a global variable containing the file presently being edited.
    It is defined in the private part of notepad.h:

    \snippet snippets/widgets-tutorial/notepad/notepad.h 6

    \c setText("") clears the text buffer.

    \section2 Opening a file

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

    Complete method \c on_actionOpen_triggered().

    \snippet snippets/widgets-tutorial/notepad/notepad.cpp 3

    \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 current_file 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 \a text.
    \c setText(text) fille the buffer of our editor with \c text.

    \c 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 \c {Go to Slot}.

    \snippet snippets/widgets-tutorial/notepad/notepad.cpp 4

    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.

    \c section2 Saving a file with \c {Save as}

    \snippet snippets/widgets-tutorial/notepad/notepad.cpp 5

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


    \section2 Print a file

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

    QT       += core gui printsupport

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

    \section2 Select a font

        \snippet snippets/widgets-tutorial/notepad/notepad.cpp 7

    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, redo

    If you select some text, and want to copy it to the clipboard,
    you call the appropriate method of 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

    This project contains the following files:

    \list
        \li {main.cpp}
        \li {notepad.cpp}
        \li {notepad.h}
        \li {notepad.pro}
        \li {notepad.ui}
    \endlist
    \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

    \section1 Building and Running Notepad

    Now that you have all the necessary files, select \b Build >
    \b {Build Project Notepad} to build and run the application. Qt Creator
    uses \c qmake and \c make to create an executable in the directory
    specified in the build settings of the project and runs it.

    \section2 Building and Running from the Command Line

    To build the application from the command line, switch to the
    directory in which you have the \c .cpp file of the application and add the
    project file (suffixed .pro) described earlier. The following shell commands
    then build the application:

    \code
        qmake
        make (or nmake on Windows)
    \endcode

    The commands create an executable in the project directory. The \c qmake tool reads the
    project file and produces a \c Makefile with instructions on how to build the application.
    The \c make tool (or the \c nmake tool) then reads the \c Makefile and produces the executable
    binary.
*/