android - 喷气背包导航 : NavHostManager is not an active fragment of FragmentManager

Question

我正在使用 Jetpack Navigation 来处理 fragment 的导航。
我一直在关注文档并安装了所需的组件，但在尝试显示托管 NavHost fragment 的 Activity 时应用程序仍然崩溃

异常:

java.lang.IllegalArgumentException: Fragment NavHostFragment{820022f} is not an active fragment of FragmentManager FragmentManager{5a5703c in HostCallbacks{a0b41c5}}
        at android.support.v4.app.FragmentManagerImpl.setPrimaryNavigationFragment(FragmentManager.java:3389)
        at android.support.v4.app.BackStackRecord.executeOps(BackStackRecord.java:783)
        at android.support.v4.app.FragmentManagerImpl.executeOps(FragmentManager.java:2595)
        at android.support.v4.app.FragmentManagerImpl.executeOpsTogether(FragmentManager.java:2382)
        at android.support.v4.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManager.java:2337)
        at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:2244)

主要 Activity 布局

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".LoginActivity" >

    <fragment
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/my_nav_host_fragment"
        android:name="androidx.navigation.fragment.NavHostFragment"
        app:navGraph="@navigation/nav_graph"
        app:defaultNavHost="true"
        />
</FrameLayout>

主要 Activity - Kotlin

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.login_activity)
        if (savedInstanceState == null) {
            supportFragmentManager.beginTransaction()
                    .replace(R.id.container, LoginFragment.newInstance())
                    .commitNow()
        }
    }

    override fun onSupportNavigateUp()
        = findNavController(R.id.my_nav_host_fragment).navigateUp()

}

我正在尝试测试 JetPack 功能，目前我被困在这个功能上，有人知道可能出了什么问题吗？是因为 Android 3.2 仍处于预览阶段吗？任何帮助将不胜感激..

Answer 1

已解决。

问题来自调用 FragmentManager 以用 LoginFragment 的新实例替换其内容，只需从 onCreate 方法中删除以下代码即可解决问题

if (savedInstanceState == null) {
    supportFragmentManager.beginTransaction()
            .replace(R.id.container, LoginFragment.newInstance())
            .commitNow()
}