如何在已实现以下代码的情况下将映射添加到MainActivity？

Question

我正在创建一个应用，该应用将允许通过计算经纬度点之间的面积来完成面积映射。这需要实现地图，但是，我不确定如何使用下面已实现的代码来实现此操作，以允许底部导航栏。我一直在努力寻找解决方案！

这是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">

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

<com.google.android.gms.maps.MapView
android:id="@+id/mapView"
android:layout_width="match_parent"
android:layout_height="400dp" />

</android.support.constraint.ConstraintLayout>

这是MainActivity.java：

package com.example.jack.farmeye;

import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.design.widget.BottomNavigationView;
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) 
   {
            switch (item.getItemId()) {
                case R.id.navigation_home:
                    mTextMessage.setText(R.string.title_home);
                    return true;
                case R.id.navigation_dashboard:
                    mTextMessage.setText(R.string.title_dashboard);
                    return true;
                 case R.id.navigation_notifications:
                mTextMessage.setText(R.string.title_notifications);
                return true;
        }
        return false;
    }
};

@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);
}





}