Bottom of NavHostFragment hidden behind BottomNavigationView

Question

I have layout with a nav bar at the bottom and the main content inside a NavHostFragment. Now the bottom of the NavHostFragment is hidden behind the nav bar. How can I fix this?

This is the main layout of the activity:

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_height="match_parent"
    android:layout_width="match_parent">

    <fragment
        android:id="@+id/nav_host_fragment"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:defaultNavHost="true"
        app:layout_constraintBottom_toTopOf="@id/nav_view"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:navGraph="@navigation/mobile_navigation" />


    <com.google.android.material.bottomnavigation.BottomNavigationView
        android:id="@+id/nav_view"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginStart="0dp"
        android:layout_marginEnd="0dp"
        android:background="?android:attr/windowBackground"
        android:layout_alignParentBottom="true"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:menu="@menu/bottom_nav_menu" />

</androidx.constraintlayout.widget.ConstraintLayout>

And one of the fragments of the nav host:

<?xml version="1.0" encoding="utf-8"?>

<androidx.core.widget.NestedScrollView
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:isScrollContainer="true"
    app:layout_constraintTop_toTopOf="parent">


    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical">

    </LinearLayout>

</androidx.core.widget.NestedScrollView>

Answer 1

I had the same problem and I found a cure. @ianhanniballake was right, but that is not a final solution. The problem is in value of 'layout_height' of NavHostFragment. You should walk through next 3 steps in activity_main.xml:

1. Be sure or remove android:paddingTop="?attr/actionBarSize" from root ConstraintLayout
2. Add app:layout_constraintTop_toBottomOf="@id/nav_host_fragment" to <BottomNavigationView>

3. Change in <fragment ... NavHostFragment>

   android:layout_height="match_parent"

to

android:layout_height="0dp"
android:layout_weight="1"

=======================

A Little investigation:

Let's create a 'Bottom Navigation Activity'-project from scratch.

Step 0.1:

add background to root of activity_main.xml

android:background="@android:color/holo_green_light"

Step 0.2: change content of fragment_home.xml to this:

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@android:color/holo_orange_dark">

    <TextView
        android:id="@+id/left_top"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="L_T"
        android:background="#ffcccc"
        android:layout_gravity="start|top"
        android:textSize="120sp" />

    <TextView
        android:id="@+id/right_bottom"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="R_B"
        android:background="#ccffcc"
        android:layout_gravity="end|bottom"
        android:textSize="120sp" />
</FrameLayout>

You will see:

Step 1: remove android:paddingTop="?attr/actionBarSize":

Step 2: Add app:layout_constraintTop_toBottomOf="@id/nav_host_fragment" constraint for BottomNavigationView

Step 3 (Final). change height to 0dp and add android:layout_weight="1" for NavHostFragment

PS.Hope this helps for other similar problems