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>

1 files changed, 9 insertions, 3 deletions

diff --git a/src/plugins/platforms/windows/qwindowsintegration.cpp b/src/plugins/platforms/windows/qwindowsintegration.cpp
index 7510cded50..ee58a19ca9 100644
--- a/src/plugins/platforms/windows/qwindowsintegration.cpp
+++ b/src/plugins/platforms/windows/qwindowsintegration.cpp
@@ -183,7 +183,6 @@ struct QWindowsIntegrationPrivate
     QOpenGLStaticContextPtr m_staticOpenGLContext;
     QWindowsInputContext m_inputContext;
     QWindowsAccessibility m_accessibility;
-    QWindowsTheme m_theme;
     QWindowsServices m_services;
 };
 
@@ -362,9 +361,16 @@ QAbstractEventDispatcher * QWindowsIntegration::guiThreadEventDispatcher() const
     return d->m_eventDispatcher;
 }
 
-QPlatformTheme *QWindowsIntegration::platformTheme() const
+QStringList QWindowsIntegration::themeNames() const
 {
-    return &d->m_theme;
+    return QStringList(QLatin1String(QWindowsTheme::name));
+}
+
+QPlatformTheme *QWindowsIntegration::createPlatformTheme(const QString &name) const
+{
+    if (name == QLatin1String(QWindowsTheme::name))
+        return new QWindowsTheme;
+    return QPlatformIntegration::createPlatformTheme(name);
 }
 
 QPlatformServices *QWindowsIntegration::services() const