Android architecture component navigation: toolbar back button missing, back not working

Question

I\'m trying the jetpack navigation and can\'t show the navigation back button when I move to a new fragment.

NavigationActivity.kt

class NavActivity : Ap         


        

Answer 1

Edit: Your DetailFragment contains the line

DataBindingUtil.setContentView<FragmentDetailBinding>(requireActivity(),
    R.layout.fragment_detail)

which is resetting the content of your Activity to only be your fragment_detail layout, wiping out the NavHostFragment and everything else.

You should be using DataBindingUtil.bind<FragmentDetailBinding>(view)!! instead.

Original answer (you should still do this, but the above answer is actually what solves the problem)

Your ConstraintLayout is missing quite a few constraints (your views should be a vertical chain, where every app:layout_constraintTop_toBottomOf has an alternative app:layout_constraintBottom_toTopOf on the other element, etc.).

Since you have a single set of three vertically aligned items, you don't need a ConstraintLayout - just a LinearLayout is enough:

<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout
    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"
    android:orientation="vertical"
    tools:context=".views.NavActivity">

    <androidx.appcompat.widget.Toolbar
        android:id="@+id/toolbar"
        android:layout_height="?attr/actionBarSize"
        android:elevation="4dp"
        android:background="?attr/colorPrimary"
        android:theme="@style/ThemeOverlay.AppCompat.ActionBar"
        app:popupTheme="@style/ThemeOverlay.AppCompat.Light"
        android:layout_width="match_parent"/>

    <fragment
        android:id="@+id/navigation_graph"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        app:defaultNavHost="true"
        app:navGraph="@navigation/navigation_graph"/>

    <com.google.android.material.bottomnavigation.BottomNavigationView
        android:id="@+id/bottom_nav_view"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:menu="@menu/menu_bottom_nav" />
</LinearLayout>