我将BottomNavigationBar（bnb）与Navigation（android jetpack）一起使用。这是一个单一活动的应用程序。有3个片段。其中之一正在开始。当我执行从起始片段到任何结尾的导航时，bnb下降一半。当我回去或在不开始的片段之间执行导航时，一切正常。

活动

<androidx.constraintlayout.widget.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="@color/colorPrimary"
    tools:context=".ui.activities.Mainactivity">

    <com.google.android.material.bottomnavigation.BottomNavigationView
        android:id="@+id/bottom_navigation_view"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:itemIconSize="@dimen/bnb_icon_size"
        android:background="?attr/colorPrimary"
        app:itemIconTint="@drawable/selector"
        app:elevation="@dimen/margin_small"
        app:layout_constraintBottom_toBottomOf="parent"
        app:menu="@menu/bottom_navigation_menu" />

    <fragment
        android:id="@+id/nav_host_fragment"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="0dp"
        android:layout_height="0dp"
        app:layout_constrainedWidth="true"
        app:layout_constrainedHeight="true"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintBottom_toTopOf="@id/bottom_navigation_view"
        app:defaultNavHost="true"
        app:navGraph="@navigation/nav_graph"/>

</androidx.constraintlayout.widget.ConstraintLayout>

其中一个片段

<layout 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">

    <data>

        <variable
            name="callback"
           type="(...)ui.info.InfoFragmentCallback" />

    </data>

    <androidx.constraintlayout.widget.ConstraintLayout
        android:id="@+id/set_coord_layout"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="@color/colorPrimaryDark"
        android:fitsSystemWindows="true">

        <TextView
            android:id="@+id/info_email"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/title_email"
            android:textColor="@color/colorWhiteOverlayTransparency45"
            android:textSize="@dimen/text_size_small"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

        <TextView
            android:id="@+id/info_contact_us_title"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_margin="@dimen/margin_medium"
            android:gravity="center"
            android:text="@string/title_contact_us"
            android:textColor="@color/colorWhiteOverlayTransparency45"
            android:textSize="@dimen/text_size_medium"
            android:textStyle="italic"
            app:layout_constrainedWidth="true"
            app:layout_constraintBottom_toTopOf="@+id/info_email"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent" />

        <TextView
            android:id="@+id/info_version"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_margin="@dimen/margin_large"
            android:gravity="center"
            android:text="@string/app_version"
            android:textColor="@color/colorWhiteOverlayTransparency45"
            android:textSize="@dimen/text_size_medium"
            android:textStyle="italic"
            app:layout_constraintBottom_toTopOf="@+id/info_email"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

        <TextView
            android:id="@+id/info_app_rate"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_margin="@dimen/margin_medium"
            android:gravity="center"
            android:text="@string/title_rate_app"
            android:textColor="@color/colorWhiteOverlayTransparency45"
            android:textSize="@dimen/text_size_medium"
            android:textStyle="italic"
            app:layout_constrainedWidth="true"
            app:layout_constraintBottom_toTopOf="@+id/info_google_badge"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent" />

        <ImageView
            android:id="@+id/info_google_badge"
            android:layout_width="wrap_content"
            android:layout_height="@dimen/icon_size_large"
            android:elevation="@dimen/margin_medium"
            android:onClick="@{(view)->callback.onAppRateclicked()}"
            android:src="@drawable/google_play_badge"
            app:layout_constraintBottom_toTopOf="@+id/info_privacy_policy"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/info_email"
            tools:ignore="ContentDescription" />


        <TextView
            android:id="@+id/info_privacy_policy"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginBottom="@dimen/margin_huge"
            android:onClick="@{(view)->callback.onPrivacyclicked()}"
            android:text="@string/privacy_policy_title"
            android:textColor="@color/colorSecondary"
            android:textSize="@dimen/text_size_small"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent" />
    </androidx.constraintlayout.widget.ConstraintLayout>
</layout>

Mainactivity

public class Mainactivity extends AppCompatactivity {

    private BottomNavigationView bottomNavigationView;

    private NavController mNavController;

    private final BottomNavigationView.OnNavigationItemReselectedListener mOnNavigationItemReselectedListener = item -> {
        /*multiple touches may must nothing*/
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mNavController = Navigation.findNavController(this,R.id.nav_host_fragment);
        bottomNavigationView = findViewById(R.id.bottom_navigation_view);
        NavigationUI.setupWithNavController(bottomNavigationView,mNavController);

        initBottomNavigationmenu();
    }

    private void initBottomNavigationmenu() {
        bottomNavigationView.setOnNavigationItemReselectedListener(mOnNavigationItemReselectedListener);
    }

    public void performNavigation(int navId) {
        mNavController.navigate(navId);
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        bottomNavigationView.setOnNavigationItemReselectedListener(null);
    }
}

bnb菜单

<menu xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">

    <item
        android:id="@+id/starting_fragment"
        android:icon="@drawable/ic_image"
        android:title=""
        app:showAsaction="ifRoom" />

    <item
        android:id="@+id/favorites_fragment"
        android:icon="@drawable/ic_star"
        android:title=""
        app:showAsaction="ifRoom"/>

    <item
        android:id="@+id/info_fragment"
        android:icon="@drawable/ic_info"
        android:title=""
        app:showAsaction="ifRoom"/>

</menu>

哪里有问题？