40.2 Declaring a Navigation Host

A navigation host is simply a special fragment (NavHostFragment) that is embedded into the user interface layout of an activity and serves as a placeholder for the destinations through which the user will navigate. Figure 40-4, for example, shows a typical activity screen and highlights the area represented by the navigation host fragment:

Figure 40-4

A NavHostFragment can be placed into an activity layout within the Android Studio layout editor either by dragging and dropping an instance from the Containers section of the palette, or by manually editing the XML as follows:

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

<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="...