使用前在bulid.gradle(app)import

     dependencies {
    implementation "androidx.navigation:navigation-fragment-ktx:2.3.0"
    implementation "androidx.navigation:navigation-ui-ktx:2.3.0"
     }

• 在 res/navigation 新增 nav_graph xml*

app:startDestination 將 fragment id="@+id/mainFragment" 指定開始的destination

<?xml version="1.0" encoding="utf-8"?>
<navigation 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/nav_graph.xml"
    app:startDestination="@id/mainFragment">

    <fragment
        android:id="@+id/mainFragment"
        android:name="com.test.TodoListFragment"
        tools:layout="@layout/fragment_todo_list" />

</navigation>

• fragment_todo_list xml*

<androidx.constraintlayout.widget.ConstraintLayout 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:clipToPadding="false"
    tools:context=".TodoListFragment">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recyclerView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:paddingBottom="60dp"
        tools:listitem="@layout/item_todo" />

    <androidx.appcompat.widget.AppCompatButton
        android:id="@+id/buttonAdd"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="@string/add_todo"
        app:layout_constraintBottom_toBottomOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

從 navigation graph 可以看到，開始頁面layout 為 fragment_todo_list：

reference :https://www.notion.so/Navigation-component-9-9-Andy-a1245a1b31c5453fbf1b28f887ec0d73
reference:https://medium.com/@wsrew2000/android-navigation-%E5%AD%B8%E7%BF%92%E7%AD%86%E8%A8%98-%E4%B8%80-%E5%9F%BA%E7%A4%8E%E4%BD%BF%E7%94%A8-3c1607ce4d38