Add function to group object to send a value only if it was changed.

src/knx/group_object.cpp

@@ -311,3 +311,13 @@ bool GroupObject::valueNoSendCompare(const KNXValue& value, const Dpt& type)
         return dataChanged;
     }
 }
+
+bool GroupObject::valueCompare(const KNXValue& value, const Dpt& type)
+{
+    if (valueNoSendCompare(value, type))
+    {
+         objectWritten();
+         return true;
+    }
+    return false;
+}

src/knx/group_object.h

@@ -173,6 +173,19 @@ class GroupObject
      * The parameters must fit the group object. Otherwise it will stay unchanged.
      */
     void value(const KNXValue& value, const Dpt& type);
+    
+    /**
+     * Check if the value (after conversion to dpt) will differ from current value of the group object and changes the state of the group object to ::WriteRequest if different.
+     * Use this method only, when the value should not be sent if it was not changed, otherwise value(const KNXValue&, const Dpt&) will do the same (without overhead for comparing)
+     * @param value the value the group object is set to
+     * @param type the datapoint type used for the conversion.
+     * 
+     * The parameters must fit the group object. Otherwise it will stay unchanged.
+     * 
+     * @returns true if the value of the group object has changed
+     */
+    bool valueCompare(const KNXValue& value, const Dpt& type);
+
     /**
      * set the current value of the group object.
      * @param value the value the group object is set to