Step 1 Add navigation components to the project

At the top of the project-level build.gradle file, along with the other ext variables, add a variable for the navigationVersion. To find the latest navigation version number, see Declaring dependencies in the Android developer documentation.

ext {
        ...
        navigationVersion = "2.3.0"
        ...
    }

In the Gradle Scripts folder, open the module-level build.gradle file. Add the dependencies for navigation-fragment-ktx and navigation-ui-ktx, as shown below:

dependencies {
  ...
  implementation "androidx.navigation:navigation-fragment-ktx:$navigationVersion"
  implementation "androidx.navigation:navigation-ui-ktx:$navigationVersion"
  ...
}

Step 2 Create the NavHostFragment

Inside the activity_main.xml layout file, your fragment now looks like the following:

<?xml version="1.0" encoding="utf-8"?>
<merge 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/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <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:navGraph="@navigation/nav" />
</merge>

in the nav

<fragment
        android:id="@+id/loginFragment"
        android:name="person.shilei.chat.login.LoginFragment"
        android:label="LoginFragment"
        tools:layout="@layout/fragment_login"/>