Add utility class for automatic scope handling for app options widget factories

src/app/CMakeLists.txt

@@ -198,6 +198,7 @@ SET(QGIS_APP_SRCS
   locator/qgslocatoroptionswidget.cpp
 
   options/qgsoptions.cpp
+  options/qgsoptionsutils.cpp
 
   gps/qgsgpsbearingitem.cpp
   gps/qgsgpsinformationwidget.cpp

src/app/devtools/qgsappdevtoolutils.h

@@ -20,9 +20,9 @@ class QgsDevToolWidgetFactory;
 #include <memory>
 
 /**
- * \ingroup core
+ * \ingroup app
  *
- * Manages lifetime of a QgsScopedDevToolWidgetFactory, automatically
+ * Manages lifetime of a QgsDevToolWidgetFactory, automatically
  * registering and unregistering it as required.
  *
  * \since QGIS 3.14

src/app/options/qgsoptionsutils.cpp

@@ -0,0 +1,36 @@
+/***************************************************************************
+    qgsoptionsutils.cpp
+    -------------------------
+    begin                : September 2020
+    copyright            : (C) 2020 by Nyall Dawson
+    email                : nyall dot dawson at gmail dot com
+ ***************************************************************************
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU General Public License as published by  *
+ *   the Free Software Foundation; either version 2 of the License, or     *
+ *   (at your option) any later version.                                   *
+ *                                                                         *
+ ***************************************************************************/
+#include "qgsoptionsutils.h"
+
+#include "qgisapp.h"
+#include "qgis.h"
+#include "qgsoptionswidgetfactory.h"
+
+QgsScopedOptionsWidgetFactory::QgsScopedOptionsWidgetFactory() = default;
+
+QgsScopedOptionsWidgetFactory::~QgsScopedOptionsWidgetFactory()
+{
+  if ( mFactory )
+    QgisApp::instance()->unregisterOptionsWidgetFactory( mFactory.get() );
+}
+
+void QgsScopedOptionsWidgetFactory::reset( std::unique_ptr<QgsOptionsWidgetFactory> factory )
+{
+  if ( mFactory )
+    QgisApp::instance()->unregisterOptionsWidgetFactory( mFactory.get() );
+  mFactory = std::move( factory );
+  if ( mFactory )
+    QgisApp::instance()->registerOptionsWidgetFactory( mFactory.get() );
+}

src/app/options/qgsoptionsutils.h

@@ -0,0 +1,42 @@
+/***************************************************************************
+    qgsoptionsutils.h
+    -------------------------
+    begin                : September 2020
+    copyright            : (C) 2020 by Nyall Dawson
+    email                : nyall dot dawson at gmail dot com
+ ***************************************************************************
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU General Public License as published by  *
+ *   the Free Software Foundation; either version 2 of the License, or     *
+ *   (at your option) any later version.                                   *
+ *                                                                         *
+ ***************************************************************************/
+#ifndef QGSOPTIONSUTILS_H
+#define QGSOPTIONSUTILS_H
+
+class QgsOptionsWidgetFactory;
+#include <memory>
+
+/**
+ * \ingroup app
+ *
+ * Manages lifetime of a QgsOptionsWidgetFactory, automatically
+ * registering and unregistering it as required.
+ *
+ * \since QGIS 3.16
+ */
+class QgsScopedOptionsWidgetFactory
+{
+  public:
+    QgsScopedOptionsWidgetFactory();
+    ~QgsScopedOptionsWidgetFactory();
+
+    void reset( std::unique_ptr< QgsOptionsWidgetFactory > factory = nullptr );
+
+  private:
+    std::unique_ptr< QgsOptionsWidgetFactory > mFactory;
+};
+
+
+#endif // QGSOPTIONSUTILS_H