How to change the size and shape of a particular bottom bar navigation item

After a few research I came across this library. They did not provide what I was looking for, but they implemented this behavior in one of their samples, which was pretty close to what I needed.

This is what I got by reusing their idea (tested only on API 23):

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It looks decent, but I do not like the implementation since the bottom navigation is now split between two components.

The idea is to create an empty item in the middle of the bottom bar, and to add a floating action button on top of it, to create the illusion that it is part of the bottom bar.

Here is the layout of my bottombar and floating navigation button:

<com.ittianyu.bottomnavigationviewex.BottomNavigationViewEx
    android:id="@+id/navigation"
    android:layout_width="match_parent"
    android:layout_height="56dp"
    android:layout_gravity="bottom"
    app:elevation="0dp"
    app:itemIconTint="@drawable/menu_item_selector"
    app:itemTextColor="@drawable/menu_item_selector"
    app:layout_constraintBottom_toBottomOf="parent"
    app:menu="@menu/navigation_items" />

<android.support.design.widget.FloatingActionButton
    android:id="@+id/fab"
    android:layout_width="70dp"
    android:layout_height="70dp"
    android:layout_marginEnd="8dp"
    android:layout_marginStart="8dp"
    android:focusable="true"
    app:backgroundTint="@color/white"
    app:borderWidth="0dp"
    app:elevation="0dp"
    app:fabSize="mini"
    app:layout_constraintBottom_toBottomOf="@id/navigation"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:srcCompat="@drawable/camera_icon" />

Navigation bar items :

    <?xml version="1.0" encoding="utf-8"?>
    <menu xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools">
    <item
        android:id="@+id/action_around_me"
        android:icon="@drawable/ic_bottombar_around_me"
        tools:ignore="MenuTitle" />

    <item
        android:id="@+id/action_my_projects"
        android:icon="@drawable/ic_bottombar_projects"
        tools:ignore="MenuTitle" />

    <!-- Here is the trick -->
    <item
        android:id="@+id/empty"
        android:enabled="false"
        tools:ignore="MenuTitle" />

    <item
        android:id="@+id/action_notifications"
        android:icon="@drawable/ic_bottombar_notification"
        tools:ignore="MenuTitle" />

    <item
        android:id="@+id/action_settings"
        android:icon="@drawable/ic_bottombar_settings"
        tools:ignore="MenuTitle" />
</menu>

Everytime I the FAB button is clicked, I disable the bottom bar :

private void disableBottomBar() {
    Menu menu = navigationBar.getMenu();
    for (int i = 0; i < menu.size(); i++) {
        // The third item is a an empty item so we do not do anything on it
        if (i != 2) {
            menu.getItem(i).setCheckable(false);
        }
    }
}

Same thing with setCheckable(true) when a bottom bar icon is clicked.

Hope this helps.

Since the last Material update (2018), it's possible to do so with native UI elements:

• BottomAppBar with app:fabAttached attribute
• FloatingActionButton with app:layout_anchor relating the BottomAppBar
• Enjoy the alignment with app:fabAlignmentMode

You can relate to this great Medium article for more new material elements and more details about this one.

Hope it helps you!

<android.support.design.widget.BottomNavigationView
    android:id="@+id/navigation"
    android:layout_width="match_parent"
    android:layout_height="56dp"
    android:layout_alignParentBottom="true"
    android:background="?android:attr/windowBackground"
    app:itemIconTint="@color/colorPrimary"
    app:itemTextColor="@android:color/black"
    app:menu="@menu/navigation"
    android:clipChildren="false">

    <android.support.design.widget.FloatingActionButton
        android:id="@+id/fab"
        android:layout_width="56dp"
        android:layout_height="56dp"
        android:layout_gravity="center"
        android:layout_marginBottom="8dp"
        app:elevation="6dp"
        android:scaleType="center" />
</android.support.design.widget.BottomNavigationView>

also add android:clipChildren="false" to root layout