[settings] add method to get value for a setting associated to an enum

this will make sure the returned value is actually an existing entry of the enum

python/core/qgssettings.sip.in

@@ -9,6 +9,7 @@
 
 
 
+
 class QgsSettings : QObject
 {
 %Docstring
@@ -220,6 +221,7 @@ An optional Section argument can be used to get a value from a specific Section.
     sipIsErr = !sipRes;
 %End
 
+
     bool contains( const QString &key, const QgsSettings::Section section = QgsSettings::NoSection ) const;
 %Docstring
 Returns true if there exists a setting called key; returns false otherwise.

src/core/qgssettings.h

@@ -18,6 +18,8 @@
 #define QGSSETTINGS_H
 
 #include <QSettings>
+#include <QMetaEnum>
+
 #include "qgis_core.h"
 #include "qgis.h"
 
@@ -216,6 +218,30 @@ class CORE_EXPORT QgsSettings : public QObject
     % End
 #endif
 
+#ifndef SIP_RUN
+
+    /**
+     * Return the setting value for a setting defined on an enum.
+     * This forces the output to be a valid and existing entry of the enum.
+     * \note The enum needs to be declared with Q_ENUM
+     */
+    template <class T>
+    T enumSettingValue( const QString &key, const T &defaultValue,
+                        const Section section = NoSection ) const
+    {
+      T v = static_cast<T>( value( key, static_cast<int>( defaultValue ), section ).toInt() );
+      QMetaEnum metaEnum = QMetaEnum::fromType<T>();
+      if ( metaEnum.isValid() )
+      {
+        if ( !metaEnum.valueToKey( static_cast<int>( v ) ) )
+        {
+          v = defaultValue;
+        }
+      }
+      return v;
+    }
+#endif
+
     /**
      * Returns true if there exists a setting called key; returns false otherwise.
      * If a group is set using beginGroup(), key is taken to be relative to that group.