Add support for QEvent::LanguageChange

Respond to the language change event by refreshing all binding
expressions. For constant string translation bindings we must now create
special QQmlBinding instances instead of a one-time property write
meta-call upon instantiation. Those however are more lightweight than an
entire JavaScript expression.

In addition this provides a slot to explicitly trigger a re-evaluation
of bindings, to make it a little easier to discover for the developer.

[ChangeLog][QtQml][QQmlEngine] Added retranslate() slot and
QEvent::LanguageChange support to refresh bindings when changing the
language at run-time.

Task-number: QTBUG-15602
Change-Id: Ide174648e1d8a5738acb88e15495018d0869d7bc
Reviewed-by: Michael Brasser <michael.brasser@live.com>

1 files changed, 24 insertions, 0 deletions

diff --git a/src/qml/qml/qqmlengine.cpp b/src/qml/qml/qqmlengine.cpp
index c0cabe4dd0..38a2978712 100644
--- a/src/qml/qml/qqmlengine.cpp
+++ b/src/qml/qml/qqmlengine.cpp
@@ -1328,6 +1328,27 @@ void QQmlEngine::setOutputWarningsToStandardError(bool enabled)
 }
 
 /*!
+  Refreshes all binding expressions that use strings marked for translation.
+
+  Call this function after you have installed a new translator with
+  QCoreApplication::installTranslator, to ensure that your user-interface
+  shows up-to-date translations.
+
+  \note Due to a limitation in the implementation, this function
+  refreshes all the engine's bindings, not only those that use strings
+  marked for translation.
+  This may be optimized in a future release.
+
+  \since 5.10
+*/
+void QQmlEngine::retranslate()
+{
+    Q_D(QQmlEngine);
+    if (QQmlContextData *firstChildContext = QQmlContextData::get(d->rootContext)->childContexts)
+        firstChildContext->refreshExpressions();
+}
+
+/*!
   Returns the QQmlContext for the \a object, or 0 if no
   context has been set.
 
@@ -1447,6 +1468,9 @@ bool QQmlEngine::event(QEvent *e)
     Q_D(QQmlEngine);
     if (e->type() == QEvent::User)
         d->doDeleteInEngineThread();
+    else if (e->type() == QEvent::LanguageChange) {
+        retranslate();
+    }
 
     return QJSEngine::event(e);
 }