导航组件销毁活动

我对导航组件有点陌生，我有多个导航图用于单独的活动。当我恢复活动时，其中两个活动被销毁。

graph.xml

<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/garden_mapping_navigation"
    app:startDestination="@id/gardens">

    <fragment
        android:id="@+id/gardens"
        android:name="com.ezyagric.extension.android.ui.gardenmapping.gardens.GardensFragment"
        android:label="Gardens"
        tools:layout="@layout/garden_mapping_garden_list">
        <action
            android:id="@+id/gardensToMapping"
            app:destination="@id/mappingFragment" />
        <action
            android:id="@+id/gardensToMapView"
            app:destination="@id/viewMapFragment" />
    </fragment>
    <fragment
        android:id="@+id/mappingFragment"
        android:name="com.ezyagric.extension.android.ui.gardenmapping.mapping.MappingFragment"
        android:label="Garden Mapping"
        tools:layout="@layout/garden_mapping_map_garden"/>
    <fragment
        android:id="@+id/viewMapFragment"
        android:name="com.ezyagric.extension.android.ui.gardenmapping.viewmap.ViewMapFragment"
        android:label="View Map"
        tools:layout="@layout/garden_mapping_view_map">
        <argument
            android:name="garden"
            app:argType="com.ezyagric.extension.android.data.db.gardens.Garden"
            app:nullable="true"
            android:defaultValue="@null" />
    </fragment>
</navigation>

activity.xml

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

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">


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


    </LinearLayout>
</layout>

Activity.java

import com.ezyagric.extension.android.R;
import com.ezyagric.extension.android.databinding.ActivityBinding;
import com.ezyagric.extension.android.ui._base.BaseActivity;

public class MappingActivity extends BaseActivity<ActivityBinding> {

    @Override
    public int getBindingVariable() {
        return 0;
    }

    @Override
    public int getLayoutId() {
        return R.layout.garden_mapping_activity;
    }

}

BaseActivity.java

public abstract class BaseActivity<T extends ViewDataBinding> extends DaggerAppCompatActivity {

    private static final String TAG = "BaseActivity";

    private T mViewDataBinding;


    /**
     * Override for set binding variable
     *
     * @return variable id
     */
    public abstract int getBindingVariable();

    /**
     * @return layout resource id
     */
    public abstract
    @LayoutRes
    int getLayoutId();


    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        performDataBinding();
    }

    public T getViewDataBinding() {
        return mViewDataBinding;
    }

    private void performDataBinding() {
        mViewDataBinding = DataBindingUtil.setContentView(this, getLayoutId());
    }

}

我哪里出问题了？

导航组件版本

    def nav_version = "2.3.0-beta01"
    implementation "androidx.navigation:navigation-fragment:$nav_version"
    implementation "androidx.navigation:navigation-ui:$nav_version"