Android中如何在两个Navigation Graph间实现页面跳转

问题背景 #

应用包含两个嵌套导航图，HomeFragment通过标签页切换shows_screen和movies_screen，现在需要实现从ShowsFragment到SettingsFragment的跳转，此前尝试添加action未生效。

现有导航图代码 #

容器导航图

<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"
    app:startDestination="@+id/main_graph">

 <fragment
        android:id="@+id/HomeFragment"
        android:name="com.test.HomeFragment"
        android:label="fragment_home"
        tools:layout="@layout/home_fragment">
        <action
            android:id="@+id/home_login"
            app:destination="@id/login_screen"
            app:popUpTo="@id/HomeFragment"
            app:popUpToInclusive="true" />
 </fragment>

 <navigation
        android:id="@+id/settings_id"
        app:startDestination="@+id/SettingsFragment">
        <fragment
            android:id="@+id/SettingsFragmentFragment"
            android:name="com.test.SettingsFragment"
            android:label="SettingsFragment">
        <action
                android:id="@+id/action_topassword"
                app:destination="@id/password_screen" />
    </fragment> 

    <fragment
            android:id="@+id/password_screen"
            android:name="com.test.PasswordFragment"
            android:label="PasswordFragment" />
</navigation>

</navigation>

home_navigation导航图

<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/home_navigation"
    app:startDestination="@+id/shows_screen">

  <fragment
        android:id="@+id/shows_screen"
        android:name="com.test.ShowsFragment"
        android:label="ShowsFragment"
        tools:layout="@layout/shows_fragment">
  </fragment>

  <fragment
        android:id="@+id/movies_screen"
        android:name="com.test.MoviesFragment"
        android:label="MoviesFragment"
        tools:layout="@layout/movies_fragment">
  </fragment>

</navigation>

HomeFragment标签切换代码

val controller =
            activity?.let { Navigation.findNavController(it, R.id.fragmentContainerView) }
        controller?.popBackStack(R.id.home_navigation, true)
val navTabId = R.id.shows_screen
controller?.navigate(navTabId)

解决方案 #

ShowsFragment属于嵌套的home_navigation导航图，SettingsFragment在容器导航图的settings_id子导航图中，跨嵌套导航图跳转需明确目标节点，具体步骤如下：

步骤1：在home_navigation中添加跳转action #

修改home_navigation里的shows_screen片段，添加指向settings_id子导航图的action：

<fragment
    android:id="@+id/shows_screen"
    android:name="com.test.ShowsFragment"
    android:label="ShowsFragment"
    tools:layout="@layout/shows_fragment">
    <!-- 添加跳转至settings导航图的action -->
    <action
        android:id="@+id/action_shows_to_settings"
        app:destination="@id/settings_id"
        <!-- 可选：清除当前home_navigation栈，避免返回时回到标签页 -->
        app:popUpTo="@id/home_navigation"
        app:popUpToInclusive="true"/>
</fragment>

步骤2：确保容器导航图导入home_navigation #

如果容器导航图未引用home_navigation，需添加<include>标签：

<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"
    app:startDestination="@+id/main_graph">

 <!-- 导入home_navigation导航图 -->
 <include app:graph="@navigation/home_navigation" />

 <!-- 原有代码保持不变 -->
 <fragment
        android:id="@+id/HomeFragment"
        android:name="com.test.HomeFragment"
        android:label="fragment_home"
        tools:layout="@layout/home_fragment">
        <action
            android:id="@+id/home_login"
            app:destination="@id/login_screen"
            app:popUpTo="@id/HomeFragment"
            app:popUpToInclusive="true" />
 </fragment>

 <navigation
        android:id="@+id/settings_id"
        app:startDestination="@+id/SettingsFragment">
        <fragment
            android:id="@+id/SettingsFragmentFragment"
            android:name="com.test.SettingsFragment"
            android:label="SettingsFragment">
        <action
                android:id="@+id/action_topassword"
                app:destination="@id/password_screen" />
    </fragment> 

    <fragment
            android:id="@+id/password_screen"
            android:name="com.test.PasswordFragment"
            android:label="PasswordFragment" />
</navigation>

</navigation>

步骤3：在ShowsFragment中执行跳转 #

在ShowsFragment的逻辑代码中调用导航action：

// 获取当前导航控制器
val navController = Navigation.findNavController(requireView())
// 执行跳转
navController.navigate(R.id.action_shows_to_settings)

替代方案：直接跳转至SettingsFragment #

若无需通过子导航图跳转，可直接指定SettingsFragment的ID（注意容器导航图中其ID为SettingsFragmentFragment）：

<!-- 在shows_screen中添加action -->
<action
    android:id="@+id/action_shows_to_settings_fragment"
    app:destination="@id/SettingsFragmentFragment"/>

代码中调用：

navController.navigate(R.id.action_shows_to_settings_fragment)

内容的提问来源于stack exchange，提问作者Nikitha