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, 38 insertions, 10 deletions

diff --git a/src/platformsupport/themes/genericunix/qgenericunixthemes.cpp b/src/platformsupport/themes/genericunix/qgenericunixthemes.cpp
index 602dd6264a..597dbde74f 100644
--- a/src/platformsupport/themes/genericunix/qgenericunixthemes.cpp
+++ b/src/platformsupport/themes/genericunix/qgenericunixthemes.cpp
@@ -77,6 +77,8 @@ void ResourceHelper::clear()
     \ingroup qpa
 */
 
+const char *QGenericUnixTheme::name = "generic";
+
 // Helper to return the icon theme paths from XDG.
 QStringList QGenericUnixTheme::xdgIconThemePaths()
 {
@@ -159,6 +161,8 @@ static inline bool readKdeSystemPalette(const QSettings &kdeSettings, QPalette *
     \ingroup qpa
 */
 
+const char *QKdeTheme::name = "kde";
+
 QKdeTheme::QKdeTheme(const QString &kdeHome, int kdeVersion) :
     m_kdeHome(kdeHome), m_kdeVersion(kdeVersion),
     m_toolButtonStyle(Qt::ToolButtonTextBesideIcon), m_toolBarIconSize(0)
@@ -329,6 +333,8 @@ QPlatformTheme *QKdeTheme::createKdeTheme()
     \ingroup qpa
 */
 
+const char *QGnomeTheme::name = "gnome";
+
 QVariant QGnomeTheme::themeHint(QPlatformTheme::ThemeHint hint) const
 {
     switch (hint) {
@@ -358,23 +364,38 @@ QVariant QGnomeTheme::themeHint(QPlatformTheme::ThemeHint hint) const
     \brief Creates a UNIX theme according to the detected desktop environment.
 */
 
-QPlatformTheme *QGenericUnixTheme::createUnixTheme()
+QPlatformTheme *QGenericUnixTheme::createUnixTheme(const QString &name)
+{
+    if (name == QLatin1String(QGenericUnixTheme::name))
+        return new QGenericUnixTheme;
+    if (name == QLatin1String(QKdeTheme::name))
+        if (QPlatformTheme *kdeTheme = QKdeTheme::createKdeTheme())
+            return kdeTheme;
+    if (name == QLatin1String(QGnomeTheme::name))
+        return new QGnomeTheme;
+    return new QGenericUnixTheme;
+}
+
+QStringList QGenericUnixTheme::themeNames()
 {
-    QPlatformTheme *result = 0;
+    QStringList result;
     if (QGuiApplication::desktopSettingsAware()) {
         switch (QGenericUnixServices::desktopEnvironment()) {
-        case QGenericUnixServices::DE_UNKNOWN:
-            break;
         case QGenericUnixServices::DE_KDE:
-            result = QKdeTheme::createKdeTheme();
+            result.push_back(QLatin1String(QKdeTheme::name));
             break;
         case QGenericUnixServices::DE_GNOME:
-            result = new QGnomeTheme;
+            result.push_back(QLatin1String(QGnomeTheme::name));
+            break;
+        case QGenericUnixServices::DE_UNKNOWN:
             break;
         }
-    }
-    if (!result)
-        result = new QGenericUnixTheme;
+        const QByteArray session = qgetenv("DESKTOP_SESSION");
+        if (!session.isEmpty() && session != "default")
+            result.push_back(QString::fromLocal8Bit(session));
+    } // desktopSettingsAware
+    if (result.isEmpty())
+        result.push_back(QLatin1String(QGenericUnixTheme::name));
     return result;
 }
 
diff --git a/src/platformsupport/themes/genericunix/qgenericunixthemes_p.h b/src/platformsupport/themes/genericunix/qgenericunixthemes_p.h
index a9db29e8cd..cabffc0212 100644
--- a/src/platformsupport/themes/genericunix/qgenericunixthemes_p.h
+++ b/src/platformsupport/themes/genericunix/qgenericunixthemes_p.h
@@ -67,11 +67,14 @@ class QGenericUnixTheme : public QPlatformTheme
 public:
     QGenericUnixTheme() {}
 
-    static QPlatformTheme *createUnixTheme();
+    static QPlatformTheme *createUnixTheme(const QString &name);
+    static QStringList themeNames();
 
     virtual QVariant themeHint(ThemeHint hint) const;
 
     static QStringList xdgIconThemePaths();
+
+    static const char *name;
 };
 
 class QKdeTheme : public QPlatformTheme
@@ -88,6 +91,8 @@ public:
     virtual const QFont *font(Font type) const
         { return m_resources.fonts[type]; }
 
+    static const char *name;
+
 private:
     QString globalSettingsFile() const;
     void refresh();
@@ -109,6 +114,8 @@ public:
     QGnomeTheme() {}
     virtual QVariant themeHint(ThemeHint hint) const;
 
+    static const char *name;
+
 private:
 };