The Nokia Asha full touch offering introduced an API called Category bar. In the UX guidelines it says that you should never, ever, in a million years place actions in there. Now why is that? Are we just trying to fool you with this guidance? No, we’re not. And this is why.
The Category bar uses permanent highlight for the currently selected category—one of the category icon buttons is always in the pressed-down state (Pro tip: See the Series 40 UI component demos to see how it’s done on the code side!). Let’s assume that we have placed an action there; if your user wants to trigger the same action twice in a row, how would that be possible when the button is pressed down after the first go? The answer is: there would be no way.
So even though it’s technically possible to place actions in the Category bar, you really shouldn’t do that because your app will become more or less unusable at that point.
Now that we agree that actions do not belong to the Category bar and that it is a navigation element (used for changing the view), let’s go through another burning issue: Category bar should remain level contextual.
Parallel view navigation basically means that all the views are on the same hierarchy level; you don’t drill down when you change the category. Since Back is following hierarchy (not history), this also means that with simple tab navigation the Back will exit the MIDlet (and not change to the previously visited category).
If you combine drill down functionality to either of your category views, you shouldn’t show the Category bar anymore when drilling down. If you did, what would happen when the user taps “Back”? Would they exit the app or move to the main level of the drilled down view? Would you change the backstepping paradigm to make it historical? The user wouldn’t know what to expect anymore.
Because of this conflict you never should show the main Category bar on any drill-down view.
To summarise the main things for the Category bar, here’s a recap from the Full touch UX checklist:
- Categories are used to provide visibility and navigation between different sub-apps, functionalities, or modes within an app.
- The functionality of the Category bar can be compared to tabs.
- The Category bar is level contextual, i.e. you should not show it when user drills down in hierarchy.
- The Category bar is not used for representing actions.
- The currently active category is highlighted.
- If there are more categories than what fits to the Category bar, the categories are accessible via the Category bar extension.
- The Category bar extension icon (three dots) is exclusively used for opening the extension view. Do not use the icon for any other category (or action in Action button 1).
- Back is part of the Category bar, positioned at the rightmost location.