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, 2 deletions

diff --git a/src/gui/kernel/qplatformintegration_qpa.cpp b/src/gui/kernel/qplatformintegration_qpa.cpp
index e8721edce7..c9ccc27ad0 100644
--- a/src/gui/kernel/qplatformintegration_qpa.cpp
+++ b/src/gui/kernel/qplatformintegration_qpa.cpp
@@ -44,6 +44,7 @@
 #include <QtGui/QPlatformFontDatabase>
 #include <QtGui/QPlatformClipboard>
 #include <QtGui/QPlatformAccessibility>
+#include <QtGui/QPlatformTheme>
 #include <QtGui/private/qguiapplication_p.h>
 #include <QtGui/private/qpixmap_raster_p.h>
 #include <QtGui/private/qplatformscreen_qpa_p.h>
@@ -315,9 +316,15 @@ void QPlatformIntegration::screenAdded(QPlatformScreen *ps)
     emit qGuiApp->screenAdded(screen);
 }
 
-class QPlatformTheme *QPlatformIntegration::platformTheme() const
+QStringList QPlatformIntegration::themeNames() const
 {
-    return 0;
+    return QStringList();
+}
+
+class QPlatformTheme *QPlatformIntegration::createPlatformTheme(const QString &name) const
+{
+    Q_UNUSED(name)
+    return new QPlatformTheme;
 }
 
 QT_END_NAMESPACE