Equally space menu items of BottomNavigationView

Question

I'm using a BottomNavigationView (from now on BNV) to switch between Fragments, but I cannot find an XML attribute or just a way to have all the items (the images) equally spaced so that they fill the entire width in all the devices.

My XML for the activity containing both the BNV (pardon the bad colouring, it's just to make it more clear):

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".Navigation">

    <!--Toolbar-->
    <android.support.v7.widget.Toolbar
        android:id="@+id/toolbar"
        android:layout_width="fill_parent"
        android:layout_height="50dp"
        android:background="@color/main_light_blue"
        app:titleTextColor="@color/white"
        android:elevation="4dp" />

    <FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        xmlns:tools="http://schemas.android.com/tools"
        android:id="@+id/main_container"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_alignParentStart="true"
        android:layout_alignParentTop="true"
        android:layout_marginStart="0dp"
        android:layout_marginTop="50dp"
        android:layout_marginBottom="57dp"
        app:layout_behavior="@string/appbar_scrolling_view_behavior"
        tools:context="MainActivity">
    </FrameLayout>

    <!--BNV-->
    <android.support.design.widget.BottomNavigationView
        android:id="@+id/footer"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:layout_marginBottom="0dp"
        app:elevation="0dp"
        app:itemBackground="@android:color/holo_orange_dark"
        android:background="@android:color/holo_orange_dark"
        app:itemIconTint="@color/black"
        app:itemTextColor="@color/black"
        app:menu="@menu/footer" />

</RelativeLayout>

the menu items:

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">

    <item
        android:id="@+id/bacheca"
        android:title="@string/bacheca"
        app:showAsAction="always"
        android:icon="@drawable/bacheca_home"
    />

    <item
        android:id="@+id/cerca"
        android:title="@string/cerca"
        app:showAsAction="always"
        android:icon="@drawable/search_black_24dp"
        />

    <item
        android:id="@+id/nuovo"
        android:title="@string/nuovo"
        android:icon="@drawable/new_post_outlined"
        app:showAsAction="always"
    />

    <item
        android:id="@+id/profilo"
        android:title="@string/profilo"
        android:icon="@drawable/account_circle_black_24dp"
        app:showAsAction="always"
    />

</menu>

The entire activity looks like this on a mobile phone:

and like this on a tablet:

Hope someone can help me on this.

EDIT: thanks to the user @GoRoS for solving the problem of having blank spaces at the left and right edges of the BNV. It has been solved just by adding android:background="@android:color/holo_orange_dark" to the BNV.

Answer 1

Ok I managed to find a solution myself, the XML attribute that solves this is

app:itemHorizontalTranslation="false"

which is default to true. This "expands" the items to fit the entire width.

Answer 2

You're just mixing concepts when referring to background colours.

app:itemBackground = Default background for each menu item.

android:background = A drawable to use as the background of the view.

Android is filling correctly the holo_orange_dark colour to every menu items you have, however, that doesn't mean it will fill the whole row. For that purpose, just use the normal android:background attribute and that's it.

That's the effect after adding the android:background="@android:color/holo_orange_dark" line to the BottomNavigationView:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        xmlns:tools="http://schemas.android.com/tools"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".Navigation">

    <!--Toolbar-->
    <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="fill_parent"
            android:layout_height="50dp"
            android:background="@color/colorPrimary"
            app:titleTextColor="@color/white"
            android:elevation="4dp" />

    <FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
                 xmlns:app="http://schemas.android.com/apk/res-auto"
                 xmlns:tools="http://schemas.android.com/tools"
                 android:id="@+id/main_container"
                 android:layout_width="match_parent"
                 android:layout_height="match_parent"
                 android:layout_alignParentStart="true"
                 android:layout_alignParentTop="true"
                 android:layout_marginStart="0dp"
                 android:layout_marginTop="50dp"
                 android:layout_marginBottom="57dp"
                 app:layout_behavior="@string/appbar_scrolling_view_behavior"
                 tools:context=".Navigation">
    </FrameLayout>

    <!--BNV-->
    <android.support.design.widget.BottomNavigationView
            android:id="@+id/footer"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_alignParentBottom="true"
            android:layout_marginBottom="0dp"
            android:background="@android:color/holo_orange_dark"
            app:elevation="0dp"
            app:itemBackground="@android:color/holo_orange_dark"
            app:itemIconTint="@color/black"
            app:itemTextColor="@color/black"
            app:menu="@menu/footer" />

</RelativeLayout>

This is what you get adding that line:

Instead, if you remove it the result is your original problem: