Android Navigation跳转首页后返回仍回到登录注册页问题求助

你遇到的问题核心原因是导航跳转配置缺失popUpTo属性，仅配置popUpToInclusive无法生效，具体修改方案如下：

1. 修正导航图跳转配置 #

跳转到HomeFragment的两个action都需要补充app:popUpTo属性，指定需要清空的回退栈范围，直接指定导航图的id即可清空所有登录注册相关的页面回退栈：

<?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"
    app:startDestination="@id/registerFragment">

    <fragment
        android:id="@+id/loginFragment"
        android:name="com.mml.mymall.LoginFragment"
        android:label="fragment_login"
        tools:layout="@layout/fragment_login">
        <action
            android:id="@+id/action_loginFragment_to_registerFragment"
            app:destination="@id/registerFragment"
            app:enterAnim="@anim/slide_in_left"
            app:exitAnim="@anim/slide_in_right"
            app:popEnterAnim="@anim/slide_out_right"
            app:popExitAnim="@anim/slide_out_left" />
        <!-- 补充app:popUpTo属性 -->
        <action
            android:id="@+id/action_loginFragment_to_homeFragment"
            app:destination="@id/homeFragment"
            app:launchSingleTop="true"
            app:popUpTo="@id/nav_graph"
            app:popUpToInclusive="true" />
        <action
            android:id="@+id/action_loginFragment_to_resetPasswordFragment"
            app:destination="@id/resetPasswordFragment"
            app:popUpTo="@id/loginFragment" />
    </fragment>
    <fragment
        android:id="@+id/registerFragment"
        android:name="com.mml.mymall.RegisterFragment"
        android:label="fragment_register"
        tools:layout="@layout/fragment_register">
        <action
            android:id="@+id/action_registerFragment_to_loginFragment"
            app:destination="@id/loginFragment"
            app:enterAnim="@anim/slide_in_left"
            app:exitAnim="@anim/slide_out_right"
            app:popEnterAnim="@anim/slide_out_right"
            app:popExitAnim="@anim/slide_out_left" />
        <!-- 补充app:popUpTo属性，同时建议把launchSingleTop也设为true -->
        <action
            android:id="@+id/action_registerFragment_to_homeFragment"
            app:destination="@id/homeFragment"
            app:launchSingleTop="true"
            app:popUpTo="@id/nav_graph"
            app:popUpToInclusive="true" />
    </fragment>
    <fragment
        android:id="@+id/homeFragment"
        android:name="com.mml.mymall.HomeFragment"
        android:label="fragment_home"
        tools:layout="@layout/fragment_home"/>
    <fragment
        android:id="@+id/resetPasswordFragment"
        android:name="com.mml.mymall.ResetPasswordFragment"
        android:label="fragment_reset_password"
        tools:layout="@layout/fragment_reset_password" />
</navigation>

2. 优化MainActivity已登录状态跳转逻辑 #

原有逻辑会直接将HomeFragment叠加在默认启动的RegisterFragment回退栈之上，导致已登录用户打开应用后点击返回仍会回到注册页，修改为直接修改导航图起始页即可：

public class MainActivity extends AppCompatActivity {

    private NavController navController;
    private FirebaseAuth firebaseAuth;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        setTheme(R.style.Theme_MyMall);
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        firebaseAuth = FirebaseAuth.getInstance();
        FirebaseUser currentUser = firebaseAuth.getCurrentUser();

        NavHostFragment navHostFragment =
                (NavHostFragment)
                        getSupportFragmentManager().findFragmentById(R.id.nav_host_fragment_container);

        navController = navHostFragment.getNavController();
        // 修改此处逻辑
        if (currentUser != null) {
            NavGraph navGraph = navController.getNavInflater().inflate(R.navigation.nav_graph);
            navGraph.setStartDestination(R.id.homeFragment);
            navController.setGraph(navGraph);
        } else {
            navController.setGraph(R.navigation.nav_graph);
        }
    }

    @Override
    public boolean onSupportNavigateUp() {
        return navController.navigateUp() || super.onSupportNavigateUp();
    }
}

原理说明 #

popUpToInclusive属性需要配合popUpTo使用才会生效：

• popUpTo用于指定回退栈需要弹出到的目标页面id
• popUpToInclusive="true"代表弹出时连popUpTo指定的目标页面也一起移除
  你之前仅配置了popUpToInclusive没有指定popUpTo，系统无法识别需要清空的回退栈范围，因此登录注册页面会一直留在回退栈中，点击返回自然会回到对应页面。

内容的提问来源于stack exchange，提问作者Dr Mido