当使用导航架构组件Android导航到目标片段时，屏幕为白色

我使用导航图从片段a导航到片段B，动画向上滑动持续时间=0.4s，但是在片段B出现之前0.4s，片段a变成白色屏幕，而不是之前保留状态数据和UI

更新： 我尝试在所有屏幕上克隆一个带有背景色配置的示例项目。我发现当导航到片段B时，片段A被删除并替换为片段B，因此在0.4s期间，包含片段的主活动布局可以通过其背景色看到

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
        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:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="#F1E78C"
        tools:context="com.myricseptember.countryfact.ui.MainActivity">

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

</android.support.constraint.ConstraintLayout>

=>如何自定义导航添加片段（而不是删除替换）或自定义句柄在片段B事务启动后删除A？
我通过添加配置修复了白色屏幕：app:enterAnim=“@anim/slide\u up”app:exitAnim=“@anim/no\u anim”app:popeneranim=“@anim/no\u anim”app:popExitAnim=“@anim/slide\u down”
    <?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="#123456">

    <android.support.v7.widget.RecyclerView
            android:id="@+id/countryRecyclerView"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_alignParentStart="true"
            android:layout_alignParentTop="true"
            app:layoutManager="android.support.v7.widget.LinearLayoutManager"
            tools:listitem="@layout/layout_list_item" />
</RelativeLayout>

    <?xml version="1.0" encoding="utf-8"?>

<ScrollView 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:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="#CAEACB">


    <android.support.constraint.ConstraintLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent">

    </android.support.constraint.ConstraintLayout>
</ScrollView>

<?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/countryfact_navigation_graph"
        app:startDestination="@id/countryListFragment">

    <fragment
            android:id="@+id/countryListFragment"
            android:name="com.myricseptember.countryfact.ui.list.CountryListFragment"
            android:label="Country Fact"
            tools:layout="@layout/fragment_country_list">
        <action
                android:id="@+id/action_countryListFragment_to_countryDetailsFragment"
                app:destination="@id/countryDetailsFragment"
                app:enterAnim="@anim/slide_up"
                app:popExitAnim="@anim/slide_down" />
    </fragment>
    <fragment
            android:id="@+id/countryDetailsFragment"
            android:name="com.myricseptember.countryfact.ui.details.CountryDetailsFragment"
            android:label="CountryDetailsFragment"
            tools:layout="@layout/fragment_country_details" />
    />
</navigation>