FragmentStateAdapter 和 ViewPager2 加载片段的速度比 FragmentStatePagerAdapter 和 ViewPager 慢

Question

在我的应用程序中，我显示了可以滚动到上个月和下个月的月历列表。在滑动到上一个和下一个时，如果我使用 FragmentStatePagerAdapter 和 ViewPager，我的片段可以顺利加载，没有任何延迟，但它现在已被弃用。所以，我更新了

ViewPager 到 ViewPager2 

FragmentStatePagerAdapter 到 FragmentStateAdapter 

更新后，我可以看到在上下滑动时加载片段有延迟。但是相同的代码可以顺利地使用 FragmentStatePagerAdapter 和 ViewPager。 我也试过mViewPager2.setOffscreenPageLimit(//Interger Value//)，但没有帮助。

请帮助我。

fragment_employee_months_holder

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <androidx.viewpager2.widget.ViewPager2
        android:id="@+id/fragment_months_viewpager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:clickable="true"
        android:focusable="true" />

    <ProgressBar
        android:id="@+id/progressBar"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"
        android:backgroundTint="@color/colorPrimary" />

</RelativeLayout>

EmployeeSummaryAdapter

class EmployeeSummaryAdapter(
    fragment: Fragment,
    private val mCodes: List<String>,
    private val mListener: NavigationListener,
    private val progressBarInterface: ProgressBarInterface
) : FragmentStateAdapter(fragment) {

    private val mFragments = SparseArray<EmployeeSummaryFragment>()

    override fun createFragment(position: Int): EmployeeSummaryFragment {
        val bundle = Bundle()
        val code = mCodes[position]
        bundle.putString(DAY_CODE, code)

        val fragment = EmployeeSummaryFragment(progressBarInterface)
        fragment.arguments = bundle
        fragment.listener = mListener
        mFragments.put(position, fragment)
        
        return fragment
    }

    override fun getItemCount(): Int = mCodes.size

    override fun getItemId(position: Int): Long {
        return position.toLong()
    }
}

EmployeeSummaryFragmentHolder

class EmployeeSummaryFragmentHolder : MyFragmentHolder(), NavigationListener, ProgressBarInterface {

    private var viewPager2: ViewPager2? = null
    private lateinit var mEmployeeSummaryAdapter: EmployeeSummaryAdapter
    private lateinit var mView: View

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        currentDayCode = Formatter.getTodayCode()
    }

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        mView = inflater.inflate(R.layout.fragment_employee_months_holder, container, false)
        viewPager2 = mView.fragment_months_viewpager
        viewPager2!!.id = (System.currentTimeMillis() % 100000).toInt()

        Handler(Looper.getMainLooper()).postDelayed({
            setupFragment()
        }, 0)

        return mView
    }

    private fun setupFragment() {
        val codes = getMonths(currentDayCode)
        mEmployeeSummaryAdapter = EmployeeSummaryAdapter(this, codes, this, this)
        viewPager2.apply {
            viewPager2!!.adapter = mEmployeeSummaryAdapter

            val myPageChangeCallback = object : ViewPager2.OnPageChangeCallback() {
                override fun onPageScrollStateChanged(state: Int) { }
                override fun onPageScrolled(position: Int, positionOffset: Float, 
                                              positionOffsetPixels: Int) { }
                override fun onPageSelected(position: Int) {   }
            }
            viewPager2!!.registerOnPageChangeCallback(myPageChangeCallback)
        }
    }
}

EmployeeSummaryFragment

class EmployeeSummaryFragment(val progressBarInterface: ProgressBarInterface) :
    Fragment(), MonthlyCalendar {

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        val view = inflater.inflate(R.layout.fragment_employee_month, container, false)
        ...
        ...        
        return view
    }

    override fun onResume() {
        super.onResume()
        ...
        ...
    }
}

Answer 1

我试图查看您的代码，但没有发现任何可疑之处，但您肯定需要将您的 mViewPager2.setOffscreenPageLimit(//Interger Value//) 设置为您的 EmployeeSummaryFragmentHolder。

viewpager2.offscreenPageLimit = 2