// Copyright (C) 2016 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only

/*!
    \example arrowpad
    \ingroup examples-linguist
    \examplecategory {User Interface Components}

    \title Arrow Pad Example

    \brief Understanding the Qt Linguist \e contexts concept and using two
    or more languages.

    \image linguist-arrowpad_en.png {Screenshot of Arrow Pad in English}

    We will use two translations, French and Dutch, although there is no
    effective limit on the number of possible translations that can be used
    with an application.

    When using qmake, the relevant lines in \c arrowpad.pro are:

    \snippet arrowpad/arrowpad.pro 0
    \codeline
    \snippet arrowpad/arrowpad.pro 1

    When using CMake, the relevant lines in \c CMakeLists.txt are:
    \snippet arrowpad/CMakeLists.txt 0
    \codeline
    \snippet arrowpad/CMakeLists.txt 1

    Run \c lupdate. It should produce two identical message files
    \c arrowpad_fr.ts and \c arrowpad_nl.ts. These files will contain all the source
    texts marked for translation with \c tr() calls and their contexts.

    When using qmake, \c lupdate must be run manually:

    \snippet doc/snippets/doc_src_examples_arrowpad.qdoc 0

    When using CMake, build the \c update_translations target to run \c lupdate:

    \snippet doc/snippets/doc_src_examples_arrowpad.qdoc 4

    See the \l{Qt Linguist Manual} for more information about
    translating Qt applications.

    \section1 Line by Line Walkthrough

    In \c arrowpad.h we define the \c ArrowPad subclass which is a
    subclass of QWidget. In the screenshot above, the central
    widget with the four buttons is an \c ArrowPad.

    \snippet arrowpad/arrowpad.h 0
    \snippet arrowpad/arrowpad.h 1
    \snippet arrowpad/arrowpad.h 2

    When \c lupdate is run it not only extracts the source texts but it
    also groups them into contexts. A context is the name of the class in
    which the source text appears. Thus, in this example, "ArrowPad" is a
    context: it is the context of the texts in the \c ArrowPad class.
    The \c Q_OBJECT macro defines \c tr(x) in \c ArrowPad like this:

    \snippet doc/snippets/doc_src_examples_arrowpad.cpp 0

    Knowing which class each source text appears in enables \e {Qt
    Linguist} to group texts that are logically related together, e.g.
    all the text in a dialog will have the context of the dialog's class
    name and will be shown together. This provides useful information for
    the translator since the context in which text appears may influence how
    it should be translated. For some translations keyboard
    accelerators may need to be changed and having all the source texts in a
    particular context (class) grouped together makes it easier for the
    translator to perform any accelerator changes without introducing
    conflicts.

    In \c arrowpad.cpp we implement the \c ArrowPad class.

    \snippet arrowpad/arrowpad.cpp 0
    \snippet arrowpad/arrowpad.cpp 1
    \snippet arrowpad/arrowpad.cpp 2
    \snippet arrowpad/arrowpad.cpp 3

    We call \c ArrowPad::tr() for each button's label since the labels are
    user-visible text.

    \image linguist-arrowpad_en.png {Screenshot of Arrow Pad in English}

    \snippet arrowpad/mainwindow.h 0
    \snippet arrowpad/mainwindow.h 1

    In the screenshot above, the whole window is a \c MainWindow.
    This is defined in the \c mainwindow.h header file. Here too, we
    use \c Q_OBJECT, so that \c MainWindow will become a context in
    \e {Qt Linguist}.

    \snippet arrowpad/mainwindow.cpp 0

    In the implementation of \c MainWindow, \c mainwindow.cpp, we create
    an instance of our \c ArrowPad class.

    \snippet arrowpad/mainwindow.cpp 1

    We also call \c MainWindow::tr() twice, once for the action and
    once for the shortcut.

    Note the use of \c tr() to support different keys in other
    languages. "Ctrl+Q" is a good choice for Quit in English, but a
    Dutch translator might want to use "Ctrl+A" (for Afsluiten) and a
    German translator "Strg+E" (for Beenden). When using \c tr() for
    \uicontrol Ctrl key accelerators, the two argument form should be used
    with the second argument describing the function that the
    accelerator performs.

    Our \c main() function is defined in \c main.cpp as usual.

    \snippet arrowpad/main.cpp 2
    \snippet arrowpad/main.cpp 3

    We choose which translation to use according to the current locale.
    QLocale::system() can be influenced by setting the \c LANG
    environment variable, for example. Notice that the use of a naming
    convention that incorporates the locale for \c .qm message files,
    (and TS files), makes it easy to implement choosing the
    translation file according to locale.

    If there is no QM message file for the locale chosen the original
    source text will be used and no error raised.

    \section1 Translating to French and Dutch

    We'll begin by translating the example application into French. Start
    \e {Qt Linguist} with \c arrowpad_fr.ts. You should get the seven source
    texts ("\&Up", "\&Left", etc.) grouped in two contexts ("ArrowPad"
    and "MainWindow").

    Now, enter the following translations:

    \list
    \li \c ArrowPad
         \list
         \li \&Up - \&Haut
         \li \&Left - \&Gauche
         \li \&Right - \&Droite
         \li \&Down - \&Bas
         \endlist
    \li \c MainWindow
         \list
         \li E\&xit - \&Quitter
         \li Ctrl+Q - Ctrl+Q
         \li \&File - \&Fichier
         \endlist
    \endlist

    The \uicontrol {Done \& Next} button marks the
    translation as done and moves on to the next source text.
    It's quicker to use its short cut (see the Translation menu bar)
    after typing each translation.

    Save the file and do the same for Dutch working with \c arrowpad_nl.ts:

    \list
    \li \c ArrowPad
         \list
         \li \&Up - \&Omhoog
         \li \&Left - \&Links
         \li \&Right - \&Rechts
         \li \&Down - Omlaa\&g
         \endlist
    \li \c MainWindow
         \list
         \li E\&xit - \&Afsluiten
         \li Ctrl+Q - Ctrl+A
         \li File - \&Bestand
         \endlist
    \endlist

    We have to convert the \c tt1_fr.ts and \c tt1_nl.ts translation source
    files into QM files. We could use \e {Qt Linguist} as we've done
    before; however using the command line tool \c lrelease ensures that
    \e all the QM files for the application are created without us
    having to remember to load and \uicontrol File|Release each one
    individually from \e {Qt Linguist}.

    Type

    \snippet doc/snippets/doc_src_examples_arrowpad.qdoc 1

    when using CMake, type

    \snippet doc/snippets/doc_src_examples_arrowpad.qdoc 5

    This should create both \c arrowpad_fr.qm and \c arrowpad_nl.qm.

    To use \c arrowpad_fr.qm, change your system language to French.
    In Unix, one of the two following commands should work:

    \snippet doc/snippets/doc_src_examples_arrowpad.qdoc 2

    In Windows or Mac, set your display language to French.

    When you run the program, you should now see the French version:

    \image linguist-arrowpad_fr.png {Screenshot of Arrow Pad in French}

    Try the same with Dutch (use \c LANG=nl in Unix). Now the Dutch
    version should appear:

    \image linguist-arrowpad_nl.png {Screenshot of Arrow Pad in Dutch}

    \section1 Exercises

    Mark one of the translations in \e {Qt Linguist} as not done, i.e.
    by unchecking the "done" checkbox; run \c lupdate, then \c lrelease,
    then the example. What effect did this change have?

    Set \c LANG=fr_CA (French Canada) and run the example program again.
    Explain why the result is the same as with \c LANG=fr.

    Change one of the accelerators in the Dutch translation to eliminate the
    conflict between \e \&Bestand and \e \&Boven.
*/
