Add support for Android bottom navigation bar in Xamarin.Forms

[lukemcnally84]

The latest Material Design guidelines talk about a bottom navigation bar:
https://material.io/guidelines/components/bottom-navigation.html#

This is available within Android as the BottomNavigationView:
https://developer.android.com/reference/android/support/design/widget/BottomNavigationView.html

When can we expect to see this supported in Xamarin.Forms? Ideally, this would be available via the TabbedPage control, as suggested here:
https://forums.xamarin.com/discussion/84565/bottomnavigationview-option-for-tabbedpage-on-android

[ChaseFlorell]

I really like this, but I have a question.

Does Top Nav get deprecated for Android or is it maintained as default. Should there be a UseLegacy flag to maintain the old way and set bottom nav as the new default?

tabbedPage.On<Android>().UseLegacyTopNavigation();

It would be a breaking change if introduced as the new default, so maybe it gets rolled out in two stages.

V2.x

tabbedPage.On<Android>().UseBottomNavigation();

V3.x

[Obsolete("this is now the default")]
public void UseBottomNavitation() {}

//
tabbedPage.On<Android>().UseLegacyTopNavigation();

[dhaligas]

I think there should be both or essentially have a tabbed view that is the top tab
it is common in android to combine both top and bottom

[pcdus]

Any news about this request? A bottom TabbedPage is required if we look UI of the latest apps!

[samhouts]

Hey, I know this issue is older, but we do have an official spec open on #1675 and a PR open on #1748, so I'll go ahead and close this issue. Please follow #1675 and/or #1748 for updates. Thanks!

[Charuwaka]

tabbedPage.On().UseBottomNavigationView() will this work in 3.0 Pre or should i specify Enum position >