BottomNavigationView+ViewPager实现页面滑动

如图所示，在androidstudio中新建一个Bottom Navigation Activity

修改布局中的内容

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingTop="?attr/actionBarSize">

    <androidx.viewpager.widget.ViewPager
        android:id="@+id/view_Pager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>
    <com.google.android.material.bottomnavigation.BottomNavigationView
        android:id="@+id/nav_view"
        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/bottom_nav_menu" />

</androidx.constraintlayout.widget.ConstraintLayout>

在menu/bottom_nav_menu中加入android:orderInCategory用来指定值

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">

    <item
        android:orderInCategory="0"
        android:id="@+id/navigation_home"
        android:icon="@drawable/ic_home_black_24dp"
        android:title="@string/title_home" />

    <item
        android:orderInCategory="1"
        android:id="@+id/navigation_dashboard"
        android:icon="@drawable/ic_dashboard_black_24dp"
        android:title="@string/title_dashboard" />

    <item
        android:orderInCategory="2"
        android:id="@+id/navigation_notifications"
        android:icon="@drawable/ic_notifications_black_24dp"
        android:title="@string/title_notifications" />

</menu>

class MainActivity : AppCompatActivity() {

    private lateinit var viewPager:ViewPager
    private  var fragment= ArrayList<Fragment>()

    @SuppressLint("ResourceType")
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        viewPager=findViewById(R.id.view_Pager)
        val navView: BottomNavigationView = findViewById(R.id.nav_view)
        //menu/bottom_nav_menu.xml里加的android:orderInCategory属性就是下面item.getOrder()取的值
        navView.setOnNavigationItemSelectedListener {
            viewPager.currentItem = it.getOrder()
            return@setOnNavigationItemSelectedListener true
        }

        viewPager.adapter=MyFrgAdapter(supportFragmentManager)
        viewPager.addOnPageChangeListener(object :ViewPager.OnPageChangeListener{
            @SuppressLint("MissingSuperCall")
            override fun onPageScrolled(
                position: Int,
                positionOffset: Float,
                positionOffsetPixels: Int,
            ) {}
//当通过viewpager滑动的时候，菜单会根据滑动来改变状态
            override fun onPageSelected(position: Int) {
               navView.menu.getItem(position).setChecked(true) }

            override fun onPageScrollStateChanged(state: Int) {}

        })
    }
}

class MyFrgAdapter(val fragmentManager: FragmentManager):FragmentPagerAdapter(fragmentManager) {
    override fun getCount(): Int {
        return 3
    }

    override fun getItem(position: Int): Fragment {
        when (position) {
            0 -> {
                return HomeFragment()
            }
            1 -> {
                return DashboardFragment()
            }
            2 -> {
                return NotificationsFragment()
            }
        }
        return HomeFragment()
    }
}