Add Qt.uiLanguage and QJSEngine::uiLanguage properties

[ChangeLog][QtQml] Added Qt.uiLanguage and QJSEngine::uiLanguage properties

These properties mirror the same value in QML and C++ and can be used
freely. They also provide API symmetry to Qt for MCUs.
QQmlApplicationEngine binds to this property and applies translations
accordingly by constructing a QLocale with the value and using
QTranslator::load(locale).

Change-Id: Id87d6ee64679b07ff3cb47844594e8eeebd8c8b6
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>
Reviewed-by: Christian Kamm <mail@ckamm.de>

1 files changed, 27 insertions, 10 deletions

diff --git a/src/qml/qml/qqmlapplicationengine.cpp b/src/qml/qml/qqmlapplicationengine.cpp
index 7f80fe5e1c..7d961cd0c7 100644
--- a/src/qml/qml/qqmlapplicationengine.cpp
+++ b/src/qml/qml/qqmlapplicationengine.cpp
@@ -50,6 +50,7 @@ QT_BEGIN_NAMESPACE
 QQmlApplicationEnginePrivate::QQmlApplicationEnginePrivate(QQmlEngine *e)
     : QQmlEnginePrivate(e)
 {
+    uiLanguage = QLocale().bcp47Name();
 }
 
 QQmlApplicationEnginePrivate::~QQmlApplicationEnginePrivate()
@@ -72,6 +73,7 @@ void QQmlApplicationEnginePrivate::init()
                &QCoreApplication::quit, Qt::QueuedConnection);
     q->connect(q, &QQmlApplicationEngine::exit, QCoreApplication::instance(),
                &QCoreApplication::exit, Qt::QueuedConnection);
+    q->connect(q, SIGNAL(uiLanguageChanged()), q_func(), SLOT(_q_loadTranslations()));
 #if QT_CONFIG(translation)
     QTranslator* qtTranslator = new QTranslator(q);
     if (qtTranslator->load(QLocale(), QLatin1String("qt"), QLatin1String("_"), QLibraryInfo::location(QLibraryInfo::TranslationsPath), QLatin1String(".qm")))
@@ -83,20 +85,27 @@ void QQmlApplicationEnginePrivate::init()
     QCoreApplication::instance()->setProperty("__qml_using_qqmlapplicationengine", QVariant(true));
 }
 
-void QQmlApplicationEnginePrivate::loadTranslations(const QUrl &rootFile)
+void QQmlApplicationEnginePrivate::_q_loadTranslations()
 {
 #if QT_CONFIG(translation)
-    if (rootFile.scheme() != QLatin1String("file") && rootFile.scheme() != QLatin1String("qrc"))
+    if (translationsDirectory.isEmpty())
         return;
 
-    QFileInfo fi(QQmlFile::urlToLocalFileOrQrc(rootFile));
-
     Q_Q(QQmlApplicationEngine);
-    QTranslator *translator = new QTranslator(q);
-    if (translator->load(QLocale(), QLatin1String("qml"), QLatin1String("_"), fi.path() + QLatin1String("/i18n"), QLatin1String(".qm")))
-        QCoreApplication::installTranslator(translator);
-    else
-        delete translator;
+
+    QScopedPointer<QTranslator> translator(new QTranslator);
+    if (!uiLanguage.isEmpty()) {
+        QLocale locale(uiLanguage);
+        if (translator->load(locale, QLatin1String("qml"), QLatin1String("_"), translationsDirectory, QLatin1String(".qm"))) {
+            if (activeTranslator)
+                QCoreApplication::removeTranslator(activeTranslator.data());
+            QCoreApplication::installTranslator(translator.data());
+            activeTranslator.swap(translator);
+        }
+    } else {
+        activeTranslator.reset();
+    }
+    q->retranslate();
 #else
     Q_UNUSED(rootFile)
 #endif
@@ -106,7 +115,14 @@ void QQmlApplicationEnginePrivate::startLoad(const QUrl &url, const QByteArray &
 {
     Q_Q(QQmlApplicationEngine);
 
-    loadTranslations(url); //Translations must be loaded before the QML file is
+    if (url.scheme() == QLatin1String("file") || url.scheme() == QLatin1String("qrc")) {
+        QFileInfo fi(QQmlFile::urlToLocalFileOrQrc(url));
+        translationsDirectory = fi.path() + QLatin1String("/i18n");
+    } else {
+        translationsDirectory.clear();
+    }
+
+    _q_loadTranslations(); //Translations must be loaded before the QML file is
     QQmlComponent *c = new QQmlComponent(q, q);
 
     if (dataFlag)
@@ -181,6 +197,7 @@ void QQmlApplicationEnginePrivate::finishLoad(QQmlComponent *c)
       \list
           \li Translation files must have "qml_" prefix e.g. qml_ja_JP.qm.
       \endlist
+  \li Translations are reloaded when the \c QJSEngine::uiLanguage / \c Qt.uiLanguage property is changed.
   \li Automatically sets an incubation controller if the scene contains a QQuickWindow.
   \li Automatically sets a \c QQmlFileSelector as the url interceptor, applying file selectors to all
   QML files and assets.