Hi Christian,

The rules for inheriting @DataFields are the same regardless of the visibility of the field. A @Templated bean inherits all @DataFields from it's superclasses. If any of @DataFields in a superclass do not have a data-field in the html template of the subclass, you should see an error. If you see any behaviour deviating from this, I encourage you to report it as a bug.

After watching your video I checked out your code and the disappearing header is unrelated to inheritance. The problem is that the relevant three types, FooViewImpl, BarViewImpl, and Header, are all singletons. When the first page, FooViewImpl, Errai UI attaches the Header to this bean. When you click the button to navigate to BarViewImpl it is lazily loaded for the first time, and Errai UI attaches the header to it. But because there is only a single Header instance, attaching it to BarViewImpl removes it from FooViewImpl. You can make your sample code work by either making the Header dependent (so that foo and bar get their own headers) or by making both FooViewImpl and BarViewImpl depenent (so that a new instance is created each time so that the header is reattached whenever the page is loaded).

Cheers.

If every page has dependent header/footer etc. components then those need to be initialized completely every time I navigate.

My general advice is don't make any UI components singleton unless there is something really expensive happening when initialized, and even then try and refactor so that the expensive operation is not part of the UI component. For example if some network trip is required (like an RPC) when a component is initialized, pull that out into a separate service with a cache. Most of the time this will have negligible impact on performance.

Or if you want the header and footer to literally be on every page, you could just manually add them to the host page around the navigation panel instead of having them be in your @Pages. Here is an example of adding a navigation bar above the nav panel.

Also, I see this kind of warning message all the time, I think this is something fairly normal to do:

 

10:59:24 WARNING [TemplateUtil] WARNING: Replacing Element type [DIV] with type [PAPER-BUTTON] ErraiConsoleLogHandler.java:79

We print these warnings whenever an element in a template is overridden by a @DataField with a different element name to help users diagnose problems where there template renders unexpectedly in the compiled application.