Google's Material Design constantly evolves, and the latest updates to the spec to specify how to best use bottom navigation.
The official Material Design guidelines now reflect specific recommendations that you should start to see soon in some apps. Google recently brought this feature into its Google Photos update with a navigation bar for photos, albums, and the assistant. Google+ also did the same, with quick access to collections and communities.
But the bottom bar isn't meant to be just a clone of iOS, which has long embraced this scheme. Google has specific animation recommendations: the bar should fade to the bottom and off the screen while scrolling and reappear when moving back up.
Additionally, the icons on the bottom bar are to navigate when tapped, but Google doesn't want any lateral motion when switching between columns (no need for motion sickness).
Google favors text labels for such buttons, but they obviously shouldn't be so long to crowd the space.
Expect to start seeing some of these changes as Google implements it into apps where it makes sense and developers are able to grapple with how such design might improve navigation.
The impact on you: Learning more about Google's design philosophy is one of the ways to raise your Android Fu. You may not be ready to wireframe design concepts, but the more you know about how Material Design works and see its evolution, the better you'll be able to navigate through Android apps. You may also get irritated at times by developers who drag their feet when it comes to implementing the latest design guidelines.
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