How to change Android App theme at runtime like Google Inbox App?

Question

The inbox app features a navigation drawer. Upon clicking on any navigation drawer item a fragment is loaded (most probably) and during this transaction the app theme changes. Changing app theme requires setTheme() method to be called before setContentView(..) in the onCreate() method of the activity. The super fluid UI indicate the use of fragments so how is this achieved without recreating parent activity (otherwise there would have been a lag for sure).

The snooze fragment hase oragne like theme

The inbox fragment has blue like them

Answer 1

You can actually change the theme's style, but only before calling setContentView(@ResId int) method. Something like this perhaps?

getTheme().applyStyle(isDashUser ? R.style.redStatusBar : R.style.blackStatusBar, true);
setContentView(R.layout.my_activity);

Answer 2

If you look closely when changing the page there's a slight graduation between the two colours. This probably suggests they have a system separate from theming to re-colour all the UI elements.

One my apps has a very similar colour change feature, and I just have methods set up to manually re-apply the relevant colours to each UI element. Of course Google probably have some super slick way of doing it that they'll never share with anyone.