前言

最近接触到竖向整页滑动的需求，发现了viewpager2，虽然可以用如下方式

   val pagerSnapHelper = PagerSnapHelper()
   pagerSnapHelper.attachToRecyclerView(recycler_view)

也可以实现，官方给的viewpager2也是封装了recyclerview，用法也类似recyclerview，但是viewpager2支持fragment，保留了viewpager的特性, 就学一下比较比较。

用法

   <androidx.viewpager2.widget.ViewPager2
    android:layout_width="match_parent"     
    android:layout_height="match_parent"
    android:orientation="vertical"
    />

对于fragment

public class PagerDemoFragmentStateAdapter(fragmentActivity: FragmentActivity) : FragmentStateAdapter(fragmentActivity) {
    private val fragments = SparseArray<Fragment>()

    fun initData() {
        fragments.put(0, LiveFragment())
        notifyDataSetChanged()
    }

    override fun getItemCount(): Int = fragments.size()

    override fun createFragment(position: Int): Fragment {
        return fragments.get(position)
    }

}

  override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
setContentView(R.layout.activity_pager_demo_list)
        viewpager.orientation = ViewPager2.ORIENTATION_VERTICAL
        val adapter = PagerDemoFragmentStateAdapter(this).apply {
            initData()
        }
        viewpager.adapter = adapter
        viewpager.registerOnPageChangeCallback(object : ViewPager2.OnPageChangeCallback() {
            override fun onPageScrolled(position: Int, positionOffset: Float, positionOffsetPixels: Int) {

            }

            override fun onPageSelected(position: Int) {
            }

            override fun onPageScrollStateChanged(state: Int) {
            }
        })

    }

    fun changeViewPagerScrollState(boolean canScroll){
        // 是否禁止用户滑动页面
        viewpager.isUserInputEnabled = canScroll
    }

类似recyclerview的用法，adapter和recyclerview完全一样

class PagerDemoListAdapter(val activity: Activity) : RecyclerView.Adapter<PagerDemoListAdapter.Companion.DemoListItemViewHolder>() {
    private var list: MutableList<RoomModelListItem> = mutableListOf()

    fun initData(item: RoomModelListItem) {
        this.list.add(item)
        notifyDataSetChanged()
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): DemoListItemViewHolder {
        val view = LayoutInflater.from(parent.context).inflate(R.layout.pager_demo_item, parent, false)
        return DemoListItemViewHolder(view, activity)
    }

    override fun onBindViewHolder(holder: DemoListItemViewHolder, position: Int) {
        holder.bindData(list[position])
    }

    override fun getItemCount() = list.size

    fun changeState(position: Int, state: RoomModelState) {
        list[position].roomModelState = state
    }

    companion object {
        class DemoListItemViewHolder(itemView: View, val activity: Activity) : RecyclerView.ViewHolder(itemView) {
            val txt: TextView = itemView.findViewById(R.id.textView)
            fun bindData(item: RoomModelListItem) {
            }
        }
    }
}

        viewpager.orientation = ViewPager2.ORIENTATION_VERTICAL
        val adapter = PagerDemoListAdapter(this, this).apply {
            initData(RoomModelListItem(RoomManager.getInstance().getmRoomModel(), RoomModelState.SHOWING))
        }
        viewpager.adapter = adapter

后记

1. item的布局必须是match_parent
2. viewpager2无法根据position获得当前的viewholder