Refactor theme plugin loading.

In the old implementation, the QPlatformIntegration was asked
for the theme first, so there was no way of overriding that
by a custom plugin. Also, there was a memory leak in case
the platform theme was actually created by a plugin.

QGuiApplication now asks the QPlatformIntegration for a list
of potential theme names first, tries to load them using
the plugin loader and finally invokes a factory method of
QPlatformIntegration in case that fails. The theme is now
owned by QGuiApplication.

In the XCB plugin, the environment variable DESKTOP_SESSION
is queried and appended to the list of themes, making it possible
to load plugins for other session types.

Change-Id: I1a4b4e061815bca16c65b23e591bb7563a3e44e2
Reviewed-by: Samuel Rødal <samuel.rodal@nokia.com>

2 files changed, 10 insertions, 6 deletions

diff --git a/src/plugins/platforms/xcb/qxcbintegration.cpp b/src/plugins/platforms/xcb/qxcbintegration.cpp
index fe33bd7153..0db9ef9e64 100644
--- a/src/plugins/platforms/xcb/qxcbintegration.cpp
+++ b/src/plugins/platforms/xcb/qxcbintegration.cpp
@@ -88,8 +88,7 @@ QT_BEGIN_NAMESPACE
 
 QXcbIntegration::QXcbIntegration(const QStringList &parameters)
     : m_eventDispatcher(createUnixEventDispatcher()),
-      m_services(new QGenericUnixServices),
-      m_theme(QGenericUnixTheme::createUnixTheme())
+      m_services(new QGenericUnixServices)
 {
     QGuiApplicationPrivate::instance()->setEventDispatcher(m_eventDispatcher);
 
@@ -277,9 +276,14 @@ QPlatformServices *QXcbIntegration::services() const
     return m_services.data();
 }
 
-QPlatformTheme *QXcbIntegration::platformTheme() const
+QStringList QXcbIntegration::themeNames() const
 {
-    return m_theme.data();
+    return QGenericUnixTheme::themeNames();
+}
+
+QPlatformTheme *QXcbIntegration::createPlatformTheme(const QString &name) const
+{
+    return QGenericUnixTheme::createUnixTheme(name);
 }
 
 QT_END_NAMESPACE
diff --git a/src/plugins/platforms/xcb/qxcbintegration.h b/src/plugins/platforms/xcb/qxcbintegration.h
index 457f90d6e0..4c335f2f06 100644
--- a/src/plugins/platforms/xcb/qxcbintegration.h
+++ b/src/plugins/platforms/xcb/qxcbintegration.h
@@ -85,7 +85,8 @@ public:
 
     QPlatformServices *services() const;
 
-    QPlatformTheme *platformTheme() const;
+    QStringList themeNames() const;
+    QPlatformTheme *createPlatformTheme(const QString &name) const;
 
 private:
     QList<QXcbConnection *> m_connections;
@@ -103,7 +104,6 @@ private:
 #endif
 
     QScopedPointer<QPlatformServices> m_services;
-    QScopedPointer<QPlatformTheme> m_theme;
 };
 
 QT_END_NAMESPACE