按下后退按钮时，BottomNavigationView项目图标不会更改为相应的片段

Question

我将BottomNavigationView添加到项目中，并针对BottomNavigationView中的三个图标实现了三个片段。我还使用了addToBackStack（），以便用户可以使用“后退”按钮导航回到早期的片段。现在的问题是，当我按下“后退”按钮时，它返回到先前的片段，但是相应的BottomNavigationView图标没有被激活，它保持了最后一次单击的图标的激活状态。

相关代码在下面共享。

MainActivity.java

import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.design.widget.BottomNavigationView;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentTransaction;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.AppCompatActivity;
import android.view.MenuItem;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

private TextView mTextMessage;

private BottomNavigationView.OnNavigationItemSelectedListener mOnNavigationItemSelectedListener
        = new BottomNavigationView.OnNavigationItemSelectedListener() {

    @Override
    public boolean onNavigationItemSelected(@NonNull MenuItem item) {
        int id = item.getItemId();
        displaySelectedFragment(id);
        return true;
    }
};

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

    mTextMessage = (TextView) findViewById(R.id.message);
    BottomNavigationView navigation = (BottomNavigationView) findViewById(R.id.navigation);
    navigation.setOnNavigationItemSelectedListener(mOnNavigationItemSelectedListener);
    displaySelectedFragment(R.id.navigation_home);
}
private void displaySelectedFragment(int id){
    Fragment fragment=null;
    switch (id) {
        case R.id.navigation_home:
            fragment = new Home();
            break;
        case R.id.navigation_dashboard:
            fragment = new DashBoard();
            break;
        case R.id.navigation_notifications:
            fragment = new Notification();
            break;
    }
    if (fragment != null) {
        FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
        ft.replace(R.id.content_main, fragment);
        ft.addToBackStack(null);
        ft.commit();
    }
}

@Override
public void onBackPressed() {
    BackPressFragment fragment = ((BackPressFragment)
            getSupportFragmentManager().findFragmentById(R.id.content_main));
    if (fragment != null) {
        fragment.onBackPressed();
    }
}

}

家庭片段代码如下。

public class Home extends Fragment implements BackPressFragment{

@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container,
                         @Nullable Bundle savedInstanceState) {
    return inflater.inflate(R.layout.home_fragment, container, false);
}


@Override
public void onBackPressed() {
    AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
    builder.setMessage("Are you sure you want to exit?")
            .setCancelable(false)
            .setPositiveButton("Yes", new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface dialog, int which) {
                    getActivity().finish();
                }
            })
            .setNegativeButton("No", new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface dialog, int which) {
                    dialog.cancel();
                }
            });
    AlertDialog alertDialog = builder.create();
    alertDialog.show();
}
}

类似地，下面给出了其他两个片段，分别命名为DashBoard和NotificationFragment。

/*----------------------------DashBoard Fragment-------------------------*/
public class DashBoard extends Fragment implements BackPressFragment {

public static DashBoard newInstance() {
    return new DashBoard();
}

@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container,
                         @Nullable Bundle savedInstanceState) {
    return inflater.inflate(R.layout.dash_board_fragment, container, false);
}

@Override
public void onBackPressed() {
    if(getActivity().getSupportFragmentManager().getBackStackEntryCount()>0)
        getActivity().getSupportFragmentManager().popBackStack();
}
}
/*--------------------------------------------------------------------*/
/*--------------------Notification Fragment---------------------------*/
public class Notification extends Fragment implements BackPressFragment{

@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container,
                         @Nullable Bundle savedInstanceState) {
    return inflater.inflate(R.layout.notification_fragment, container, false);
}
@Override
public void onBackPressed() {
    if(getActivity().getSupportFragmentManager().getBackStackEntryCount()>0)
        getActivity().getSupportFragmentManager().popBackStack();
}
}

BackPressFragment.java接口

public interface BackPressFragment {
void onBackPressed();
}

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:id="@+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">

<include layout="@layout/content_main"/>

<android.support.design.widget.BottomNavigationView
    android:id="@+id/navigation"
    android:layout_width="0dp"
    android:layout_height="wrap_content"
    android:layout_marginStart="0dp"
    android:layout_marginEnd="0dp"
    android:background="?android:attr/windowBackground"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintRight_toRightOf="parent"
    app:menu="@menu/navigation" />

</android.support.constraint.ConstraintLayout>

In the given Screenshot the current Fragment is Dashboard, but the active icon in the BottomNavigationView is 'Notification'

请提出建议。