Jetpack导航:NavHostManager不是FragmentManager的活动片段

Question

我正在使用Jetpack Navigation来处理Fragments的导航.
我一直在关注文档并安装了所需的组件,当尝试显示托管NavHost片段的活动时,应用程序仍然崩溃

例外:

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)

主要活动布局

<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>

主要活动 - 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的功能,而我目前仍然坚持这一点,任何人都有一个线索可能是错的？这是因为Android 3.2还在预览中吗？任何帮助将非常感激..

Answer 1

解决了.

问题来自对FragmentManager的调用,用LoginFragment的一个新实例替换它的内容,只需从onCreate方法中删除以下代码就可以解决它

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