Add public API for setting and getting the style from C++

TODO: setup QtLabsControls C++ module docs

Task-number: QTBUG-50787
Change-Id: I382bad34df88d13fb9a74b3d2f9203280dfb4a66
Reviewed-by: Mitch Curtis <mitch.curtis@theqtcompany.com>

1 files changed, 168 insertions, 0 deletions

diff --git a/src/controls/qquickstyle.cpp b/src/controls/qquickstyle.cpp
new file mode 100644
index 00000000..e6be5efd
--- /dev/null
+++ b/src/controls/qquickstyle.cpp
@@ -0,0 +1,168 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: http://www.qt.io/licensing/
+**
+** This file is part of the Qt Labs Controls module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL3$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see http://www.qt.io/terms-conditions. For further
+** information use the contact form at http://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPLv3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or later as published by the Free
+** Software Foundation and appearing in the file LICENSE.GPL included in
+** the packaging of this file. Please review the following information to
+** ensure the GNU General Public License version 2.0 requirements will be
+** met: http://www.gnu.org/licenses/gpl-2.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "qquickstyle.h"
+#include "qquickstyleattached_p.h"
+
+#include <QtCore/qsettings.h>
+#include <QtGui/private/qguiapplication_p.h>
+#include <QtQml/private/qqmlmetatype_p.h>
+#include <QtQml/qqmlfile.h>
+
+QT_BEGIN_NAMESPACE
+
+/*!
+    \class QQuickStyle
+    \brief The QQQuickStyle class allows configuring the application style.
+    \inmodule QtLabsControls
+
+    QQuickStyle provides API for querying and configuring the application
+    \l {Styling Qt Labs Controls}{styles} of Qt Labs Controls.
+
+    \code
+    #include <QGuiApplication>
+    #include <QQmlApplicationEngine>
+    #include <QQuickStyle>
+
+    int main(int argc, char *argv[])
+    {
+        QGuiApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
+        QGuiApplication app(argc, argv);
+
+        QQuickStyle::setStyle("Material");
+
+        QQmlApplicationEngine engine;
+        engine.load(QUrl("qrc:/main.qml"));
+
+        return app.exec();
+    }
+    \endcode
+
+    \note The style must be configured \b before loading QML that imports
+    Qt Labs Controls. It is not possible to change the style after the QML
+    types have been registered.
+
+    \sa {Styling Qt Labs Controls}
+*/
+
+struct QQuickStyleSpec
+{
+    QQuickStyleSpec() : resolved(false) { }
+
+    QString name()
+    {
+        if (!resolved)
+            resolve();
+        return style.mid(style.lastIndexOf(QLatin1Char('/')) + 1);
+    }
+
+    QString path()
+    {
+        if (!resolved)
+            resolve();
+        QString s = style;
+        if (QQmlFile::isLocalFile(s))
+            s = QQmlFile::urlToLocalFileOrQrc(s);
+        return s.left(s.lastIndexOf(QLatin1Char('/')) + 1);
+    }
+
+    void setStyle(const QString &s)
+    {
+        style = s;
+        resolved = !s.isEmpty();
+    }
+
+    void resolve()
+    {
+        style = QGuiApplicationPrivate::styleOverride;
+        if (style.isEmpty())
+            style = QString::fromLatin1(qgetenv("QT_LABS_CONTROLS_STYLE"));
+        if (style.isEmpty()) {
+            QSharedPointer<QSettings> settings = QQuickStyleAttached::settings(QStringLiteral("Controls"));
+            if (settings)
+                style = settings->value(QStringLiteral("Style")).toString();
+        }
+        resolved = QGuiApplication::instance();
+    }
+
+    bool resolved;
+    QString style;
+};
+
+Q_GLOBAL_STATIC(QQuickStyleSpec, styleSpec)
+
+/*!
+    Returns the name of the application style.
+
+    \note The application style can be specified by passing a \c -style command
+          line argument. Therefore \c name() may not return a fully resolved
+          value if called before constructing a QGuiApplication.
+*/
+QString QQuickStyle::name()
+{
+    return styleSpec()->name();
+}
+
+/*!
+    Returns the path of an overridden application style, or an empty
+    string if the style is one of the built-in Qt Labs Controls styles.
+
+    \note The application style can be specified by passing a \c -style command
+          line argument. Therefore \c path() may not return a fully resolved
+          value if called before constructing a QGuiApplication.
+*/
+QString QQuickStyle::path()
+{
+    return styleSpec()->path();
+}
+
+/*!
+    Sets the application style.
+
+    \note The style must be configured \b before loading QML that imports Qt Labs Controls.
+          It is not possible to change the style after the QML types have been registered.
+*/
+void QQuickStyle::setStyle(const QString &style)
+{
+    if (QQmlMetaType::isModule(QStringLiteral("Qt.labs.controls"), 1, 0)) {
+        qWarning() << "ERROR: QQuickStyle::setStyle() must be called before loading QML that imports Qt Labs Controls.";
+        return;
+    }
+
+    styleSpec()->setStyle(style);
+}
+
+QT_END_NAMESPACE