QQuickStyle: add API for managing style paths

In order to be able to use/refer to/select styles by name:

   - ./myapp -style Glossy
   - :/qtquickcontrols2.conf: [Controls] Style=Glossy
   - QT_QUICK_CONTROLS_STYLE=Glossy ./myapp

the style needs to be available in a place where QQC2 can find it
by the given name. Normally, QQC2 scans for available styles in the
QT_INSTALL_QML/QtQuick/Controls.2/ directory, where all the built-in
styles reside. However, 3rd party styles may want to install styles
into their own namespace, especially if they offer style-specific API.

If a style is installed elsewhere, QQC2 needs to be made aware of the
style path to make it possible to locate the style. Previously, the
QT_QUICK_CONTROLS_STYLE_PATH environment variable was the only way.
This adds proper C++ API, inspired by QQmlEngine's importPathList
and pluginPathList, to manage QQC2 style paths.

[ChangeLog][Controls][QQuickStyle] Added stylePathList() and
addStylePath() methods for managing the list of directories where
Qt Quick Controls 2 searches for available styles.

Task-number: QTBUG-67062
Change-Id: I1e85b5e09ba869483c0937ac61a0a2dcfc8e774e
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>

1 files changed, 2 insertions, 0 deletions

diff --git a/src/quickcontrols2/qquickstyle.h b/src/quickcontrols2/qquickstyle.h
index ab79c3e0..ce55b76b 100644
--- a/src/quickcontrols2/qquickstyle.h
+++ b/src/quickcontrols2/qquickstyle.h
@@ -51,6 +51,8 @@ public:
     static void setStyle(const QString &style);
     static void setFallbackStyle(const QString &style);
     static QStringList availableStyles();
+    static QStringList stylePathList();
+    static void addStylePath(const QString &path);
 };
 
 QT_END_NAMESPACE