[Engine-devel] Some notes on UI composition

[Vojtech Szocs]

Hi guys,

I've encountered an interesting pattern while working on a recent patch: some View classes actually embed other View classes, and add those embedded Views to the (top-level) View.

For example, ImportVmPopupView has a field "ImportVmGeneralSubTabView generalView", which is created as part of constructor and added to ImportVmPopupView's layout.

The bottom line is, please don't use this pattern. Views are architectural components in Model-View-Presenter which are living in a particular scope (e.g. singleton/non-singleton), so UI composition should be always done on Widget level, instead of View level.

In other words, ImportVmPopupView shouldn't embed ImportVmGeneralSubTabView, but instead embed UI (Widgets) similar to ImportVmGeneralSubTabView. In case embedded View's UI is complex, we can just create a reusable widget that would be used in both ImportVmPopupView and ImportVmGeneralSubTabView.

Otherwise, we could run into problems, especially since ImportVmPopupView is dialog-specific (non-singleton) and ImportVmGeneralSubTabView is sub-tab-specific (singleton). In Model-View-Presenter, View != immediate Widget, View == MVP component wrapping UI (Widget) and bound to a specific scope, so that's the reason why UI composition should be always done on Widget level (on the other hand, subclassing Views is perfectly OK).

Sorry for being police man here .. it's just a note to keep in mind for future :)

Regards,
Vojtech