FragmentContainerView 作为 NavHostFragment

Question

似乎使用 FragmentContainerView 不能立即使用？

<androidx.fragment.app.FragmentContainerView
        class="androidx.navigation.fragment.NavHostFragment"
        android:id="@+id/fragment_nav_host"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:defaultNavHost="true"
        app:navGraph="@navigation/nav_app" />

这是我使用 fragment-ktx:1.2.0-rc01 的代码，但我总是收到此错误：

Caused by: java.lang.IllegalStateException: Activity ...MainActivity@797467d does not have a NavController set on 2131296504

只需使用 <fragment> 就可以了，据我所知，它应该被 FragmentContainerView 替换。

我是不是遗漏了什么或者是否有人可以将 FragmentContainerView 用作 NavHostFragment？

非常感谢！

Answer 1

由于这个错误报告： https://issuetracker.google.com/issues/142847973

这是唯一的方法（目前）：

val navHostFragment = supportFragmentManager
    .findFragmentById(R.id.my_nav_host_fragment) as NavHostFragment
val navController = navHostFragment.navController

(Java):

NavHostFragment navHostFragment =
    (NavHostFragment) getSupportFragmentManager()
        .findFragmentById(R.id.my_nav_host_fragment);
NavController navController = navHostFragment.getNavController();

Answer 2

使用 android:name 而不是 class。有效。

<androidx.fragment.app.FragmentContainerView
    android:name="androidx.navigation.fragment.NavHostFragment"
    ...

Answer 3

我所做的是等待 NavHostFragment 膨胀它的视图：

科特林：

super.onCreate(savedInstanceState)

// Set up the form and list.
setContentView(R.layout.activity_xxx)

// Set up navigation - action bar and sidebar.
/// Let the navigation view check/uncheck the menu items.
nav_view.post { // wait for NavHostFragment to inflate
    val navController = findNavController()
    nav_view.setupWithNavController(navController)
    nav_view.setNavigationItemSelectedListener(this)
}

Java8（使用 lambda）：

navigationView.post(() -> { // wait for NavHostFragment to inflate
    navController = Navigation.findNavController(activity, R.id.nav_host_fragment);
    NavigationUI.setupWithNavController(navView, navController);
    navView.setNavigationItemSelectedListener(navItemSelectedListener);
});

Answer 4

2020 年 8 月更新

这里是the official Android documentation推荐的解决方案。

Kotlin 版本：

val navHostFragment = supportFragmentManager.findFragmentById(R.id.nav_host_fragment) as NavHostFragment
val navController = navHostFragment.navController

Java版本：

NavHostFragment navHostFragment = supportFragmentManager.findFragmentById(R.id.nav_host_fragment);
NavController navController = navHostFragment.getNavController();

我引用文档：

When creating the NavHostFragment using FragmentContainerView or if manually adding the NavHostFragment to your activity via a FragmentTransaction, attempting to retrieve the NavController in onCreate() of an Activity via Navigation.findNavController(Activity, @IdRes int) will fail. You should retrieve the NavController directly from the NavHostFragment instead.

Ove Stoerholt 报告的 bug-report 将不会修复。您可以看到 here“无法修复（不可行）”状态。

Answer 5

我在使用kotlin时遇到了同样的问题：

val navHostFragment = supportFragmentManager.findFragmentById(R.id.nav_host_fragment) as NavHostFragment

val navController = navHostFragment.navController

只需将其添加到

setupActionBarWithNavController(navController)

FragmentContainerView 作为 NavHostFragment

FragmentContainerView as NavHostFragment

navigation

android

fragment