权限

implementation 'com.google.android.material:material:1.0.0'

1.新建一个叫menu的文件包
2.在menu中添加bottom_nav_menu.xml布局

    <item
        android:id="@+id/navigation_home"
        android:icon="@android:drawable/ic_menu_camera"
        android:title="Home" />

    <item
        android:id="@+id/navigation_dashboard"
        android:icon="@android:drawable/ic_dialog_email"
        android:title="email" />

    <item
        android:id="@+id/navigation_notifications"
        android:icon="@android:drawable/ic_dialog_map"
        android:title="sss" />

在activity_main.xml布局文件中加入

 <com.google.android.material.bottomnavigation.BottomNavigationView
        android:id="@+id/nav"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:menu="@menu/bottom_nav_menu"/>

mainActivity.java文件夹

package com.example.fu1118;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;

public class MainActivity extends AppCompatActivity {
private BottomNavigationView nav;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
nav=findViewById(R.id.nav);
nav.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {
            @Override
            public boolean onNavigationItemSelected(@NonNull MenuItem menuItem) {
                switch (menuItem.getItemId() ){
                    case R.id.navigation_home:
                        webView.loadUrl("file:///android_asset/new.html");
                    case R.id.navigation_dashboard:
                        webView.loadUrl("https://www.baidu.com");
                }
                return true;
            }
        });
    }
//添加关联菜单的部分
  @Override
    public boolean onCreateOptionsMenu(Menu menu){
        getMenuInflater().inflate(R.menu.bottom_nav_menu, menu);
        return true;
}
  @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.navigation_home:
                webView.loadUrl("file:///android_asset/new.html");
                break;
            case R.id.navigation_dashboard:
                webView.loadUrl("https://www.baidu.com");
                break;
        }
        return true;
    }
}