Mason Chen

You should get toolbaritem list from your current page by var ToolbarItems = this.GetToolbarItems().OfType().ToList(); and then add the new toolbaritem to the above list

@gazwinter if you are doing it in your page model, get the toolbar item list by this.CurrentPage.ToolbarItems. Also to let toolbar appear, current page must be in a navigation.

do you have a minimum sample that can reproduce this problem?

Please double check the sample application. I can not reproduce this problem in sample application.