Android 底部导航栏（三、ViewPager+TabLayout+Fragment）简单易懂

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<layout xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools">
    <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="@color/white"
        android:orientation="vertical">
 
        
            android:id="@+id/nav_text"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginTop="20dp"
            android:gravity="center"
            android:padding="4dp"
            android:text="ViewPager+TabLayout+Fragment"
            android:textColor="@color/black"
            android:textSize="18sp"
            android:textStyle="bold" />
 
        <androidx.viewpager.widget.ViewPager //承载内容
            android:id="@+id/fragment_container_viewpager"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_above="@id/nav_tablayout"
            android:layout_below="@id/nav_text" />
 
        <View
            android:layout_width="match_parent"//只是个分割线
            android:layout_height="0.3dp"
            android:layout_above="@id/nav_tablayout"
            android:background="@color/tab_color_false"/>
 
        <com.google.android.material.tabs.TabLayout
            android:id="@+id/nav_tablayout"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_alignParentBottom="true"
            android:background="@color/white"
            app:tabBackground="@color/white"
            app:tabIndicatorAnimationMode="elastic"
            app:tabIndicatorColor="@color/blue"
            app:tabIndicatorFullWidth="false"
            app:tabIndicatorGravity="bottom"
            app:tabMode="fixed"
            app:tabRippleColor="@android:color/transparent"
            app:tabSelectedTextColor="@color/black"
            app:tabTextColor="@color/bar_grey"
            tools:layout_height="50dp"
        />
    RelativeLayout>
layout>

class NavViewPagerTabActivity : BaseBindActivity<NavViewpagerTablayoutActivityLayoutBinding>() {
 
    override val layout: Int
        get() = R.layout.nav_viewpager_tablayout_activity_layout
 
    private lateinit var homeFragment: HomeFragment
    private lateinit var toolsFragment: ToolsFragment
    private lateinit var relaxFragment: RelaxFragment
    private lateinit var viewPager: ViewPager
    private lateinit var tabLayout: TabLayout
    private lateinit var meFragment: MineFragment
    private lateinit var playFragment: PlayFragment
    private lateinit var fragments: Array
    private val titles = arrayOf("首页", "视频", "用户")
 
 
    override fun initView() {
        initFragment()//初始化fragment列表
        viewPager = mBinding.fragmentContainerViewpager
        tabLayout = mBinding.navTablayout
        tabLayout.setupWithViewPager(viewPager)//绑定viewpager
//        for (element in titles) tabLayout.addTab(tabLayout.newTab().setText(element))
        viewPager.adapter = object :FragmentPagerAdapter(supportFragmentManager,BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT){
            override fun getCount(): Int {
                return fragments.size
            }
            override fun getItem(position: Int): Fragment {
                return fragments[position]
            }
            override fun getPageTitle(position: Int): CharSequence {
                return titles[position]
            }
        }
    }
    private fun initFragment() {
        homeFragment = HomeFragment()
        toolsFragment = ToolsFragment()
        relaxFragment = RelaxFragment()
        meFragment = MineFragment()
        playFragment = PlayFragment()
//        fragments = arrayOf(homeFragment, toolsFragment, playFragment, relaxFragment, meFragment)
        fragments = arrayOf(homeFragment, toolsFragment, meFragment)
    }
}