Separate entity classes on different files

lib/entity_class/select_entity.class.dart

@@ -0,0 +1,39 @@
+part of '../main.dart';
+
+class SelectEntity extends Entity {
+  List<String> _listOptions = [];
+  String get initialValue => _attributes["initial"] ?? null;
+
+  SelectEntity(Map rawData) : super(rawData) {
+    if (_attributes["options"] != null) {
+      _attributes["options"].forEach((value){
+        _listOptions.add(value.toString());
+      });
+    }
+  }
+
+  @override
+  void sendNewState(newValue) {
+    eventBus.fire(new ServiceCallEvent(_domain, "select_option", _entityId,
+        {"option": "$newValue"}));
+  }
+
+  @override
+  Widget _buildActionWidget(bool inCard, BuildContext context) {
+    return Container(
+      width: Entity.INPUT_WIDTH,
+      child: DropdownButton<String>(
+        value: _state,
+        items: this._listOptions.map((String value) {
+          return new DropdownMenuItem<String>(
+            value: value,
+            child: new Text(value),
+          );
+        }).toList(),
+        onChanged: (_) {
+          sendNewState(_);
+        },
+      ),
+    );
+  }
+}