setState not updating the Icon

[smbpunt]

Describe the bug
I have a variable in my AppState, and I would like to change an icon depending on this variable, after a setState().
It seems the icon is changing only if I go to another page...

To Reproduce
Steps to reproduce the behavior:

1. Have a variable in your AppState (here it's List<Message> newMessages)
2. Have an Icon based on this variable :

    List<BottomBarWithSheetItem> lstItems = [
      BottomBarWithSheetItem(
          icon: container.state.newMessages?.isEmpty ? Icons.mail_outline : Icons.mark_email_unread_outlined,
          label: 'MESSAGES'),
      //...
    ];

    return SafeArea(
      child: BottomBarWithSheet(
        controller: _bottomBarController,
       // ...
        items: lstItems,
      )

3. Have an action to update your variable, and setState()

  void checkNewMessages() async {
      //...
          this.setState(() {
            state.newMessages.add(msg);
          });
  }

Expected behavior
After calling checkNewMessages, the Icon should be mark_email_unread_outlined, but it says mail_outline.

Maybe it's not a bug, maybe It's my code the bug, but I've not find anything in your documentation regarding this...

Thanks