Android viewpager2 选项卡布局与 FragmentStateAdapter

Question

我正在使用带有选项卡布局的 ViewPager2。 这是我的MainFragment代码 -

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    super.onViewCreated(view, savedInstanceState)

    binding.viewPager.adapter = MyPagerAdapter(requireActivity())
    TabLayoutMediator(
        binding.tabLayout,  binding.viewPager
    ) { tab, position ->
        binding.viewPager.setCurrentItem(0, true)
        when (position) {
            0 -> tab.text = “Tab A”
            1 -> tab.text = “Tab B”      
        }
    }.attach()
}


private class MyPagerAdapter(fragmentActivity: FragmentActivity) :
    FragmentStateAdapter(fragmentActivity) {
    private val items = 2
    override fun getItemCount(): Int {
        return items
    }

    override fun createFragment(position: Int): Fragment = when (position) {
        0 -> FragmentA()
        1 -> FragmentB()
        else -> FragmentA()
    }
}

我这里有两个问题-

1. override fun createFragment(position: Int): Fragment每次创建MainFragment视图时，Fragment 都会创建子 Fragment 的新实例。 有没有办法重用已经存在的子片段实例？

2. 在我的导航图中，我有MainFragment及其子FragmentA和FragmentB 。 为什么我不能使用导航操作从其父级打开子级？ 如果是， override fun createFragment(position: Int): Fragment需要返回一个 Fragment 并且findNavController().navigate()不返回任何内容。 我该怎么做呢？

Answer 1

您可以按照此示例代码进行操作，这可能会对您有所帮助

class TvShowsFragment：片段（R.layout.tvshows_fragment）{

private var _binding: TvshowsFragmentBinding? = null
private val binding get() = _binding!!

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    super.onViewCreated(view, savedInstanceState)

    _binding = TvshowsFragmentBinding.bind(view)

    setUpViewPager()
    setHasOptionsMenu(true)
}

private fun setUpViewPager() {
    val viewPager = binding.vpTvShows
    val tab = binding.tlTvShows
    val adapterTv = TvAdapter(this)
    viewPager.adapter = adapterTv

    TabLayoutMediator(tab, viewPager) { tabText, position ->
        tabText.text = when (position) {
            0 -> getString(R.string.title_tvAiringToday)
            1 -> getString(R.string.title_tvOnTheAir)
            2 -> getString(R.string.title_popular)
            3 -> getString(R.string.title_topRated)
            else -> getString(R.string.title_tvAiringToday)

        }
    }.attach()

}

private inner class TvAdapter(fm: Fragment) : FragmentStateAdapter(fm) {

    override fun getItemCount(): Int = 4

    override fun createFragment(position: Int): Fragment {
        return when (position) {
            0 -> TvAiringTodayFragment()
            1 -> TvOnTheAirFragment()
            2 -> TvPopularFragment()
            3 -> TvTopRatedFragment()
            else -> TvAiringTodayFragment()
        }
    }

}