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/*!
    \example linguist/arrowpad
    \title Arrow Pad Example

    This example is a slightly more involved and introduces a key \e
    {Qt Linguist} concept: "contexts". It also shows how to use two
    or more languages.

    \image linguist-arrowpad_en.png

    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. The relevant lines of \c arrowpad.pro are

    \snippet examples/linguist/arrowpad/arrowpad.pro 0

    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.

    See the \l{Qt Linguist manual} for more information about
    translating Qt application.

    \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 examples/linguist/arrowpad/arrowpad.h 0
    \snippet examples/linguist/arrowpad/arrowpad.h 1
    \snippet examples/linguist/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/src/snippets/code/doc.src.examples.arrowpad.qdoc 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 examples/linguist/arrowpad/arrowpad.cpp 0
    \snippet examples/linguist/arrowpad/arrowpad.cpp 1
    \snippet examples/linguist/arrowpad/arrowpad.cpp 2
    \snippet examples/linguist/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

    \snippet examples/linguist/arrowpad/mainwindow.h 0
    \snippet examples/linguist/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 examples/linguist/arrowpad/mainwindow.cpp 0

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

    \snippet examples/linguist/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
    \key 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 examples/linguist/arrowpad/main.cpp 2
    \snippet examples/linguist/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 \c .ts files), makes it easy to implement choosing the
    translation file according to locale.

    If there is no \c .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
    \o \c ArrowPad
         \list
         \o \&Up - \&Haut
         \o \&Left - \&Gauche
         \o \&Right - \&Droite
         \o \&Down - \&Bas
         \endlist
    \o \c MainWindow
         \list
         \o E\&xit - \&Quitter
         \o Ctrl+Q - Ctrl+Q
         \o \&File - \&Fichier
         \endlist
    \endlist

    It's quickest to press \key{Alt+D} (which clicks the \gui {Done \& Next}
    button) after typing each translation, since this marks the
    translation as done and moves on to the next source text.

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

    \list
    \o \c ArrowPad
         \list
         \o \&Up - \&Boven
         \o \&Left - \&Links
         \o \&Right - \&Rechts
         \o \&Down - \&Onder
         \endlist
    \o \c MainWindow
         \list
         \o E\&xit - \&Afsluiten
         \o Ctrl+Q - Ctrl+A
         \o File - \&Bestand
         \endlist
    \endlist

    We have to convert the \c tt1_fr.ts and \c tt1_nl.ts translation source
    files into \c .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 \c .qm files for the application are created without us
    having to remember to load and \gui File|Release each one
    individually from \e {Qt Linguist}.

    Type

    \snippet doc/src/snippets/code/doc.src.examples.arrowpad.qdoc 1

    This should create both \c arrowpad_fr.qm and \c arrowpad_nl.qm. Set the \c
    LANG environment variable to \c fr. In Unix, one of the two following
    commands should work

    \snippet doc/src/snippets/code/doc.src.examples.arrowpad.qdoc 2

    In Windows, either modify \c autoexec.bat or run

    \snippet doc/src/snippets/code/doc.src.examples.arrowpad.qdoc 3

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

    \image linguist-arrowpad_fr.png

    Try the same with Dutch, by setting \c LANG=nl. Now the Dutch
    version should appear:

    \image linguist-arrowpad_nl.png

    \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.
*/
