Hello tr() 范例

将小 Hello World 程序翻译成拉丁语。

屏幕截图展示 English 版。

见 Qt Linguist 手册了解翻译 Qt 应用程序的更多有关信息。

逐行演练

#include <QTranslator>

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

    QTranslator translator;

创建 QTranslator object without a parent.

    Q_UNUSED(translator.load("hellotr_la"));

Tries to load a file called hellotr_la.qm (the .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.

    app.installTranslator(&translator);

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

    QPushButton hello(QPushButton::tr("Hello world!"));

Creates a push button that displays "Hello world!". If 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 拥有 tr() function. Inside a member function of a QObject class, we simply write tr("Hello world!") 而不是 QPushButton::tr("Hello world!") or QObject::tr("Hello world!") .

按英语运行应用程序

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

创建拉丁语消息文件

The first step is to create a project file that lists all the source files for the project.

When using qmake, the relevant lines in hellotr.pro 是：

SOURCES      = main.cpp
TRANSLATIONS = hellotr_la.ts

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

When using CMake, the relevant lines in CMakeLists.txt 是：

find_package(Qt6 REQUIRED COMPONENTS LinguistTools)
qt6_add_translations(hellotr
    TS_FILES hellotr_la.ts
    QM_FILES_OUTPUT_VARIABLE qm_files)
install(FILES ${qm_files} DESTINATION ${INSTALL_EXAMPLEDIR})

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

The 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 'ø' (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 lrelease program is used to convert the TS files into the QM Qt message file format. The QM format is a compact binary format designed to deliver very fast lookup performance. Both lupdate and 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 tr() function calls.

lupdate is used to create and update the message files ( hellotr_la.ts in this case) to keep them in sync with the source code. It is safe to run lupdate at any time, as lupdate does not remove any information.

试着运行 lupdate right now.

当使用 qmake 时， lupdate must be run manually:

lupdate -verbose hellotr.pro

( -verbose option instructs lupdate to display messages that explain what it is doing.)

当使用 CMake 时，构建 update_translations 目标要运行 lupdate :

cmake --build . --target update_translations

You should now have a file hellotr_la.ts in the source directory, containing this:

<!DOCTYPE TS><TS>
<context>
    <name>QPushButton</name>
    <message>
        <source>Hello world!</source>
        <translation type="unfinished"></translation>
    </message>
</context>
</TS>

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

采用 Qt Linguist 翻译成拉丁语

将使用 Qt Linguist to provide the translation, although you can use any XML or plain text editor to enter a translation into a TS file.

To start Qt Linguist , type

linguist hellotr_la.ts

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 Translation pane (the middle right of the window). Don't forget the exclamation mark!

点击 Done checkbox and choose File|Save from the menu bar. The TS file will no longer contain

<translation type='unfinished'></translation>

but instead will have

<translation>Orbis, te saluto!</translation>

按拉丁语运行应用程序

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

范例工程 @ code.qt.io