viewpager2+tablayout实现页面的切换

1.布局文件

<androidx.constraintlayout.widget.ConstraintLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent">
            <com.google.android.material.tabs.TabLayout
                android:id="@+id/tabLayout"
                app:layout_constraintTop_toTopOf="parent"
                android:layout_width="match_parent"
                android:layout_height="40dp"
                app:tabGravity="start"
                app:tabBackground="@android:color/transparent"
                app:tabRippleColor="@color/white"
                app:tabUnboundedRipple="false"
                app:tabMode="scrollable"/>

            <androidx.viewpager2.widget.ViewPager2
                android:id="@+id/viewPager"
                android:layout_width="match_parent"
                android:layout_height="0dp"
                app:layout_constraintBottom_toBottomOf="parent"
                app:layout_constraintTop_toBottomOf="@+id/tabLayout"/>
        </androidx.constraintlayout.widget.ConstraintLayout>

2.子布局tab_item_layout.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:paddingHorizontal="8dp"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:orientation="vertical">
    <View
        android:id="@+id/tv_index"
        android:layout_width="20dp"
        android:layout_height="6dp"
        android:layout_marginTop="-6dp"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/tv_name"
        android:background="@drawable/shape_6ccdff_00a8ff_3r_bg"/>
    <TextView
        android:id="@+id/tv_name"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="14sp"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        android:textColor="@color/black_333"
        android:gravity="center"
        android:maxLength="4"
        android:textStyle="bold"/>

</androidx.constraintlayout.widget.ConstraintLayout>

3.交互代码

private var mediator: TabLayoutMediator? = null
    private val mTitles = arrayOf("全部","待支付","已支付","已换绑","已完成","已取消")
    private fun initViewPager() {
        val fragments:MutableList<Fragment> = ArrayList()
        fragments.add(BuyRecordFragment.newInstance(null))
        fragments.add(BuyRecordFragment.newInstance("0"))
        fragments.add(BuyRecordFragment.newInstance("1"))
        fragments.add(BuyRecordFragment.newInstance("2"))
        fragments.add(BuyRecordFragment.newInstance("3"))
        fragments.add(BuyRecordFragment.newInstance("4"))
        mBinding.apply {
            //viewPager.offscreenPageLimit = titles.size
            viewPager.adapter = object : FragmentStateAdapter(supportFragmentManager,lifecycle) {
                override fun getItemCount(): Int {
                    return fragments.size
                }
                override fun createFragment(position: Int): Fragment {
                    //FragmentStateAdapter内部自己会管理已实例化的fragment对象,所以不需要考虑复用的问题.
                    return fragments[position]
                }
            }
            viewPager.registerOnPageChangeCallback(changeCallback)
            mediator = TabLayoutMediator(tabLayout, viewPager) { tab, position ->
                //这里可以自定义TabView
                val view = LayoutInflater.from(context).inflate(R.layout.tab_item_layout, null)
                val tv_name =view.findViewById<TextView>(R.id.tv_name)
                val tv_index =view.findViewById<View>(R.id.tv_index)
                tv_name.text = mTitles[position]
                tv_index.visibility=View.INVISIBLE
                tab.customView = view
            }
            //要执行这一句才是真正将两者绑定起来
            mediator?.attach()
        }
    }
    private val changeCallback: ViewPager2.OnPageChangeCallback = object : ViewPager2.OnPageChangeCallback() {
        override fun onPageSelected(position: Int) {
            //可以来设置选中时tab的大小
            val tabCount: Int = mBinding.tabLayout.tabCount
            for (i in 0 until tabCount) {
                val tab: TabLayout.Tab = mBinding.tabLayout.getTabAt(i)!!
                val tabView = tab.customView
                val tv_name = tabView?.findViewById<TextView>(R.id.tv_name)
                val tv_index = tabView?.findViewById<View>(R.id.tv_index)
                if (tab.position == position) {
                    if (tv_name != null) {
                        tv_name.textSize = 18f
                    }
                    if (tv_index != null) {
                        tv_index.visibility=View.VISIBLE
                    }
                } else {
                    if (tv_name != null) {
                        tv_name.textSize = 14f
                    }
                    if (tv_index != null) {
                        tv_index.visibility=View.INVISIBLE
                    }
                }
            }
        }
    }
    override fun onDestroy() {
        mediator?.detach()
        mBinding.viewPager.unregisterOnPageChangeCallback(changeCallback)
        super.onDestroy()
    }