AP_Param: added get_param_by_index

useful for parameter conversion within an object

libraries/AP_Param/AP_Param.cpp

@@ -1034,6 +1034,21 @@ bool AP_Param::find_top_level_key_by_pointer(const void *ptr, uint16_t &key)
     return false;
 }
 
+/*
+  fetch a parameter value based on the index within a group. This
+  is used to find the old value of a parameter that has been
+  removed from an object.
+*/
+bool AP_Param::get_param_by_index(void *obj_ptr, uint8_t idx, ap_var_type old_ptype, void *pvalue)
+{
+    uint16_t key;
+    if (!find_top_level_key_by_pointer(obj_ptr, key)) {
+        return false;
+    }
+    const ConversionInfo type_info = {key, idx, old_ptype, nullptr };
+    return AP_Param::find_old_parameter(&type_info, (AP_Param *)pvalue);
+}
+
 
 // Find a object by name.
 //

libraries/AP_Param/AP_Param.h

@@ -440,6 +440,13 @@ public:
     static void         convert_parent_class(uint8_t param_key, void *object_pointer,
                                              const struct AP_Param::GroupInfo *group_info);
 
+    /*
+      fetch a parameter value based on the index within a group. This
+      is used to find the old value of a parameter that has been
+      removed from an object.
+    */
+    static bool get_param_by_index(void *obj_ptr, uint8_t idx, ap_var_type old_ptype, void *pvalue);
+    
     /// Erase all variables in EEPROM.
     ///
     static void         erase_all(void);