How do I add elevation (shadow) to my BottomNavigationView. It doesn't come by default

问题

I tried setting elevation from xml and programmatically both. But nothing works.

回答1:

It only works if you set white as android:background in the BottomNavigationView.

This is my code and it's working:

<android.support.design.widget.BottomNavigationView
    android:id="@+id/bottom_navigation"
    android:layout_width="0dp"
    android:layout_height="wrap_content"
    android:layout_gravity="bottom"
    android:background="@color/white"
    app:elevation="8dp"
    app:itemIconTint="@color/bottom_color_state"
    app:itemTextColor="@color/bottom_color_state"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintHorizontal_bias="0.52"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintRight_toRightOf="parent"
    app:menu="@menu/bottom_navigation_main" />

回答2:

I got the solution. You need to add background attribute along with elevation else it wont show the shadow.

回答3:

This is the only solution that worked for me:

val background = bottomNavigation.background
if (background is MaterialShapeDrawable) {
    background.shadowCompatibilityMode = SHADOW_COMPAT_MODE_ALWAYS
}

as suggested here: https://issuetracker.google.com/issues/124153644#comment2

来源：https://stackoverflow.com/questions/40766722/how-do-i-add-elevation-shadow-to-my-bottomnavigationview-it-doesnt-come-by-d