Can add members to conversation

lib/helpers/conversations_helper.dart

@@ -49,6 +49,15 @@ class ConversationsHelper {
     return response.getObject()["conversationID"];
   }
 
+  /// Add a member to a conversation.
+  ///
+  /// Throws in case of failure
+  static Future<void> addMember(int convID, int userID) async =>
+      await APIRequest.withLogin("conversations/addMember")
+          .addInt("convID", convID)
+          .addInt("userID", userID)
+          .execWithThrow();
+
   /// Remove a member from a conversation.
   ///
   /// Throws in case of failure

lib/ui/screens/update_conversation_screen.dart

@@ -170,10 +170,7 @@ class _UpdateConversationScreen extends State<UpdateConversationScreen> {
                 keepFocusOnChoose: true,
                 label: tr("Add member"),
                 enabled: _canAddMembers,
-              onSelectUser: (user) => setState(() {
+                onSelectUser: (user) => _addMember(user)),
-                if (!_members.contains(user)) _members.insert(0, user);
-              }),
-            ),
 
             //Conversation members
             Column(
@@ -229,6 +226,20 @@ class _UpdateConversationScreen extends State<UpdateConversationScreen> {
     }
   }
 
+  void _addMember(User user) async {
+    try {
+      if (_members.contains(user)) return;
+
+      if (isUpdating)
+        await ConversationsHelper.addMember(_conversation.id, user.id);
+
+      setState(() => _members.insert(0, user));
+    } catch (e, s) {
+      logError(e, s);
+      snack(context, tr("Failed to add member to conversation!"));
+    }
+  }
+
   void _removeMember(User user) async {
     try {
       if (isUpdating)