source: trunk/doc/src/examples/hellotr.qdoc@ 268

/****************************************************************************
**
** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).
** Contact: Qt Software Information (qt-info@nokia.com)
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:LGPL$
** Commercial Usage
** Licensees holding valid Qt Commercial licenses may use this file in
** accordance with the Qt Commercial License Agreement provided with the
** Software or, alternatively, in accordance with the terms contained in
** a written agreement between you and Nokia.
**
** GNU Lesser General Public License Usage
** Alternatively, this file may be used under the terms of the GNU Lesser
** General Public License version 2.1 as published by the Free Software
** Foundation and appearing in the file LICENSE.LGPL included in the
** packaging of this file.  Please review the following information to
** ensure the GNU Lesser General Public License version 2.1 requirements
** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
**
** In addition, as a special exception, Nokia gives you certain
** additional rights. These rights are described in the Nokia Qt LGPL
** Exception version 1.0, included in the file LGPL_EXCEPTION.txt in this
** package.
**
** GNU General Public License Usage
** Alternatively, this file may be used under the terms of the GNU
** General Public License version 3.0 as published by the Free Software
** Foundation and appearing in the file LICENSE.GPL included in the
** packaging of this file.  Please review the following information to
** ensure the GNU General Public License version 3.0 requirements will be
** met: http://www.gnu.org/copyleft/gpl.html.
**
** If you are unsure which license is appropriate for your use, please
** contact the sales department at qt-sales@nokia.com.
** $QT_END_LICENSE$
**
****************************************************************************/

/*!
    \example linguist/hellotr
    \title Hello tr() Example

    This example is a small Hello World program with a Latin translation. The
    screenshot below shows the English version.

    \image linguist-hellotr_en.png

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

    \section1 Line by Line Walkthrough


    \snippet examples/linguist/hellotr/main.cpp 0

    This line includes the definition of the QTranslator class. 
    Objects of this class provide translations for user-visible text.

    \snippet examples/linguist/hellotr/main.cpp 5

    Creates a QTranslator object without a parent.

    \snippet examples/linguist/hellotr/main.cpp 6

    Tries to load a file called \c hellotr_la.qm (the \c .qm file extension is
    implicit) that contains Latin translations for the source texts used in
    the program. No error will occur if the file is not found.

    \snippet examples/linguist/hellotr/main.cpp 7

    Adds the translations from \c hellotr_la.qm to the pool of translations used
    by the program.

    \snippet examples/linguist/hellotr/main.cpp 8

    Creates a push button that displays "Hello world!". If \c hellotr_la.qm
    was found and contains a translation for "Hello world!", the
    translation appears; if not, the source text appears.

    All classes that inherit QObject have a \c tr() function. Inside
    a member function of a QObject class, we simply write \c tr("Hello
    world!") instead of \c QPushButton::tr("Hello world!") or \c
    QObject::tr("Hello world!").

    \section1 Running the Application in English

    Since we haven't made the translation file \c hellotr_la.qm, the source text
    is shown when we run the application:

    \image linguist-hellotr_en.png

    \section1 Creating a Latin Message File

    The first step is to create a project file, \c hellotr.pro, that lists
    all the source files for the project. The project file can be a qmake
    project file, or even an ordinary makefile. Any file that contains

    \snippet examples/linguist/hellotr/hellotr.pro 0
    \snippet examples/linguist/hellotr/hellotr.pro 1

    will work. \c TRANSLATIONS specifies the message files we want to
    maintain. In this example, we just maintain one set of translations,
    namely Latin.

    Note that the file extension is \c .ts, not \c .qm. The \c .ts
    translation source format is designed for use during the
    application's development. Programmers or release managers run
    the \c lupdate program to generate and update \c .ts files with
    the source text that is extracted from the source code.
    Translators read and update the \c .ts files using \e {Qt
    Linguist} adding and editing their translations.

    The \c .ts format is human-readable XML that can be emailed directly
    and is easy to put under version control. If you edit this file
    manually, be aware that the default encoding for XML is UTF-8, not
    Latin1 (ISO 8859-1). One way to type in a Latin1 character such as
    '\oslash' (Norwegian o with slash) is to use an XML entity:
    "\ø". This will work for any Unicode 4.0 character.

    Once the translations are complete the \c lrelease program is used to
    convert the \c .ts files into the \c .qm Qt message file format. The
    \c .qm format is a compact binary format designed to deliver very
    fast lookup performance. Both \c lupdate and \c lrelease read all the
    project's source and header files (as specified in the HEADERS and
    SOURCES lines of the project file) and extract the strings that
    appear in \c tr() function calls.

    \c lupdate is used to create and update the message files (\c hellotr_la.ts
    in this case) to keep them in sync with the source code. It is safe to
    run \c lupdate at any time, as \c lupdate does not remove any
    information. For example, you can put it in the makefile, so the \c .ts
    files are updated whenever the source changes.

    Try running \c lupdate right now, like this:

    \snippet doc/src/snippets/code/doc_src_examples_hellotr.qdoc 0

    (The \c -verbose option instructs \c lupdate to display messages that
    explain what it is doing.) You should now have a file \c hellotr_la.ts in
    the current directory, containing this:

    \snippet doc/src/snippets/code/doc_src_examples_hellotr.qdoc 1

    You don't need to understand the file format since it is read and
    updated using tools (\c lupdate, \e {Qt Linguist}, \c lrelease).

    \section1 Translating to Latin with Qt Linguist

    We will use \e {Qt Linguist} to provide the translation, although
    you can use any XML or plain text editor to enter a translation into a
    \c .ts file.

    To start \e {Qt Linguist}, type

    \snippet doc/src/snippets/code/doc_src_examples_hellotr.qdoc 2

    You should now see the text "QPushButton" in the top left pane.
    Double-click it, then click on "Hello world!" and enter "Orbis, te
    saluto!" in the \gui Translation pane (the middle right of the
    window). Don't forget the exclamation mark!

    Click the \gui Done checkbox and choose \gui File|Save from the
    menu bar. The \c .ts file will no longer contain

    \snippet doc/src/snippets/code/doc_src_examples_hellotr.qdoc 3

    but instead will have

    \snippet doc/src/snippets/code/doc_src_examples_hellotr.qdoc 4

    \section1 Running the Application in Latin

    To see the application running in Latin, we have to generate a \c .qm
    file from the \c .ts file. Generating a \c .qm file can be achieved
    either from within \e {Qt Linguist} (for a single \c .ts file), or
    by using the command line program \c lrelease which will produce one \c
    .qm file for each of the \c .ts files listed in the project file.
    Generate \c hellotr_la.qm from \c hellotr_la.ts by choosing
    \gui File|Release from \e {Qt Linguist}'s menu bar and pressing
    \gui Save in the file save dialog that pops up. Now run the \c hellotr
    program again. This time the button will be labelled "Orbis, te
    saluto!".

    \image linguist-hellotr_la.png
*/