Viewpager2 在第 0 个位置添加项目滚动问题

Question

在 Viewpager2 上的第 0 个位置添加项目后，该项目无法正确滚动/添加到视图，并在滚动后再次显示当前视图。将项目添加到第 0 个位置后，主要初始项目不可见。

此处为屏幕录制示例

我的

Viewpager's Adapter

看起来像下面这样。

   inner class ScreenSlidePagerAdapter(fa: FragmentActivity) : FragmentStateAdapter(fa) {
    override fun getItemCount(): Int {
        return list.size
    }

    override fun createFragment(position: Int): Fragment = ScrollFragment(list[position])

    fun addFragment(string: String) {
        list.add(string)
        notifyItemInserted(list.size)
    }

    fun addAtPreviousFragment(string: String) {
        list.add(0, string)
        notifyItemInserted(0)
    }
}

addAtPreviousFragment 

正在将视频添加到第0个位置。

ViewPager 在下一个添加项目，第 0 个位置如下所示

  mAddAtNext.setOnClickListener {
            Handler(Looper.getMainLooper()).postDelayed(
                {
                    val randomNext = (50..90).random()
                    println("randomNext >>>>>> $randomNext")
                    pagerAdapter.addFragment("Next $randomNext")

                }, 200
            )
        }

        mAddAtPrevious.setOnClickListener {
            Handler(Looper.getMainLooper()).postDelayed(
                {
                    val randomPrevious = (0..40).random()
                    println("randomPrevious >>>>>> $randomPrevious")
                    pagerAdapter.addAtPreviousFragment("Previous $randomPrevious")
                }, 200
            )
        }

相同的代码已添加到 Git Hub。

如有任何帮助，我们将不胜感激。预先感谢

Answer 1

您好，请尝试这个版本，我已经测试过并且工作正常

class MainActivity : AppCompatActivity() {

private lateinit var list: ArrayList<String>
private lateinit var pagerAdapter: ScreenSlidePagerAdapter

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)
    setUpViewPager()
}

fun setUpViewPager() {
    list = arrayListOf()
    list.add("45")
    val mViewPager: ViewPager2 = findViewById(R.id.view_pager)

    pagerAdapter = ScreenSlidePagerAdapter(this)
    mViewPager.adapter = pagerAdapter

    val mAddAtNext: AppCompatButton = findViewById(R.id.btn_next)
    val mAddAtPrevious: AppCompatButton = findViewById(R.id.btn_previous)

    pagerAdapter.submitInitialItem(list.first())
    mAddAtNext.setOnClickListener {
        val randomNext = (50..90).random()
        println("randomNext >>>>>> $randomNext")
        pagerAdapter.addFragment("Next $randomNext")
    }

    mAddAtPrevious.setOnClickListener {
        val randomPrevious = (0..40).random()
        println("randomPrevious >>>>>> $randomPrevious")
        pagerAdapter.addAtPreviousFragment("Previous $randomPrevious")
    }
}

inner class ScreenSlidePagerAdapter(fa: FragmentActivity) : FragmentStateAdapter(fa) {
    private val fragmentList: MutableList<Fragment> = mutableListOf()
    fun submitInitialItem(string: String) {
        fragmentList.add(ScrollFragment(string))
    }


    override fun getItemCount(): Int {
        return fragmentList.size
    }

    override fun createFragment(position: Int): Fragment = fragmentList[position]

    fun addFragment(string: String) {
        fragmentList.add(ScrollFragment(string))
        notifyItemInserted(fragmentList.size)
    }

    fun addAtPreviousFragment(string: String) {
        fragmentList.add(0, ScrollFragment(string))
        notifyItemInserted(0)
    }

    override fun getItemId(position: Int): Long {
        return fragmentList[position].hashCode().toLong()
    }

    override fun containsItem(itemId: Long): Boolean {
        return fragmentList.any { it.hashCode().toLong() == itemId }
    }
}

}