Allow to create new choices on survey on its creation

lib/helpers/posts_helper.dart

@@ -165,6 +165,7 @@ class PostsHelper {
       case PostKind.SURVEY:
         request.addString("question", post.survey.question);
         request.addString("answers", post.survey.answers.join("<>"));
+        request.addBool("allowNewAnswers", post.survey.allowNewChoicesCreation);
         break;
 
       case PostKind.YOUTUBE:

lib/models/new_post.dart

@@ -12,12 +12,15 @@ import 'package:meta/meta.dart';
 class NewSurvey {
   final String question;
   final Set<String> answers;
+  final bool allowNewChoicesCreation;
 
   const NewSurvey({
     @required this.question,
     @required this.answers,
+    @required this.allowNewChoicesCreation,
   })  : assert(question != null),
-        assert(answers.length > 1);
+        assert(answers.length > 1),
+        assert(allowNewChoicesCreation != null);
 }
 
 class NewPost {

lib/ui/dialogs/new_survey_dialog.dart

@@ -29,12 +29,15 @@ class __SurveyDialogState extends State<_SurveyDialog> {
   TextEditingController _questionController;
   final _choiceController = TextEditingController();
   var _choices = Set<String>();
+  var _allowNewChoices = false;
 
   bool get canConfirm =>
       _questionController.text.length > 2 && _choices.length > 1;
 
-  NewSurvey get newSurvey =>
-      NewSurvey(question: _questionController.text, answers: _choices);
+  NewSurvey get newSurvey => NewSurvey(
+      question: _questionController.text,
+      answers: _choices,
+      allowNewChoicesCreation: _allowNewChoices);
 
   @override
   void initState() {
@@ -42,7 +45,10 @@ class __SurveyDialogState extends State<_SurveyDialog> {
     _questionController = TextEditingController(
       text: widget.initialSurvey == null ? "" : widget.initialSurvey.question,
     );
-    if (widget.initialSurvey != null) _choices = widget.initialSurvey.answers;
+    if (widget.initialSurvey != null) {
+      _choices = widget.initialSurvey.answers;
+      _allowNewChoices = widget.initialSurvey.allowNewChoicesCreation;
+    }
   }
 
   @override
@@ -105,6 +111,15 @@ class __SurveyDialogState extends State<_SurveyDialog> {
                           : null,
                     )),
               ),
+
+              // Allow users to create new choices
+              ListTile(
+                leading: Switch.adaptive(
+                  value: _allowNewChoices,
+                  onChanged: (v) => setState(() => _allowNewChoices = v),
+                ),
+                title: Text(tr("Allow users to create new choices")),
+              )
             ]),
       ),
     );