FragmentContainerView 作为 NavHostFragment

Question

似乎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" />

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

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

仅使用<fragment>作品和 AFAIK，它应该被替换为FragmentContainerView.

我是不是遗漏了什么，或者有人可以FragmentContainerView用作NavHostFragment?

非常感谢！

Answer 1

由于此错误报告：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

（爪哇）：

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

Answer 2

2020 年 8 月更新

下面是Android官方文档推荐的解决方案。

科特林版本：

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

爪哇版：

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

我引用文档：

当使用 FragmentContainerView 创建 NavHostFragment或通过 FragmentTransaction手动将 NavHostFragment 添加到您的活动时，尝试通过 Navigation.findNavController(Activity, @IdRes int)检索活动的 onCreate() 中的NavController 将失败。您应该直接从 NavHostFragment 检索 NavController。

Ove Stoerholt报告的错误报告将不会被修复。您可以在此处看到“无法修复（不可行）”状态。

Answer 3

我所做的是等待NavHostFragment夸大其观点：

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（带 lambda）：

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