预期

Question

摘要：这似乎是将RecyclerView托管在底部工作表中的问题，因为父片段HomeFragment托管了子片段的另一个实例ContentFragment不会嵌套在底表中，而onRestoreInstanceState会按预期执行。

预期

以RecyclerView的{{1}}和LayoutManager方法保存并返回Fragment onSaveInstanceState的状态时，预期结果是{ {1}}将显示在与更改配置之前相同的位置。

已观察

在屏幕配置更改上，onViewStateRestored有时会显示在位置 0 而不是配置更改之前的RecyclerView位置。在某些情况下，它还能成功保留布局状态。由于随机性，这似乎涉及生命周期+底表问题。

RecyclerView在RecyclerView上登录为非null。
contentRecyclerView.layoutManager!!.onSaveInstanceState()在onSaveInstanceState上登录为非null。

savedRecyclerLayoutState

onViewStateRestored

savedRecyclerLayoutState记录为非空。

实施

层次结构

adapter由SAVED.name托管在observeContentUpdated布局中名为ContentFragment的{{1}}片段内。 HomeFragment的{{1}}布局包含BottomSheet。

正在加载保存状态

在bottomSheet情况下将数据加载到fragment_home中的ContentFragment后，调用

fragment_content。实例状态在contentRecyclerView之后设置为onRestoreInstanceState，因为Adapter中的单元格是可忽略的，并会导致数据再次加载。这样可确保还原仅在配置更改后发生一次。

HomeFragment.kt

observeContentUpdated创建一个包含已保存的片段SAVED.name的底表。

null

ContentFragment.kt

在onRestoreInstanceState方法中填充了RecyclerView。

initSavedBottomSheet

fragment_home.xml

ContentFragment

fragment_content.xml

class HomeFragment : Fragment() {

...

override fun onSaveInstanceState(outState: Bundle) {
    super.onSaveInstanceState(outState)
    outState.putParcelable(USER_KEY, user)
    outState.putBoolean(APP_BAR_EXPANDED_KEY, isAppBarExpanded)
    outState.putBoolean(SAVED_CONTENT_EXPANDED_KEY, isSavedContentExpanded)
}

override fun onViewStateRestored(savedInstanceState: Bundle?) {
    super.onViewStateRestored(savedInstanceState)
    if (savedInstanceState != null) {
        if (savedInstanceState.getBoolean(APP_BAR_EXPANDED_KEY)) appBar.setExpanded(true)
        else appBar.setExpanded(false)
        if (savedInstanceState.getBoolean(SAVED_CONTENT_EXPANDED_KEY)) {
            swipeToRefresh.isEnabled = false
            bottomSheetBehavior.state = STATE_EXPANDED
            setBottomSheetExpanded()
        }
        updateAds()
    }
}

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    homeViewModel = ViewModelProviders.of(activity!!).get(HomeViewModel::class.java)
}

override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
                          savedInstanceState: Bundle?): View? {
    binding = FragmentHomeBinding.inflate(inflater, container, false)
    binding.setLifecycleOwner(this)
    binding.viewmodel = homeViewModel
    return binding.root
}

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    super.onViewCreated(view, savedInstanceState)
    user = homeViewModel.getCurrentUser()
    ...
    observeSignIn(savedInstanceState)
    initSavedBottomSheet(savedInstanceState)
    ...
    initSwipeToRefresh()
    ...
}

override fun onActivityCreated(savedInstanceState: Bundle?) {
    super.onActivityCreated(savedInstanceState)
    if (savedInstanceState == null
            && childFragmentManager.findFragmentByTag(PRICEGRAPH_FRAGMENT_TAG) == null
            && childFragmentManager.findFragmentByTag(CONTENT_FEED_FRAGMENT_TAG) == null) {
        childFragmentManager.beginTransaction()
                .replace(priceContainer.id, PriceFragment.newInstance(), PRICEGRAPH_FRAGMENT_TAG)
                .commit()
        childFragmentManager.beginTransaction().replace(contentContainer.id,
                ContentFragment.newInstance(Bundle().apply {
                    putString(FEED_TYPE_KEY, MAIN.name)
                }), CONTENT_FEED_FRAGMENT_TAG)
                .commit()
    }
}

...

private fun initSavedBottomSheet(savedInstanceState: Bundle?) {
    bottomSheetBehavior = from(bottomSheet)
    bottomSheetBehavior.isHideable = false
    bottomSheetBehavior.peekHeight = SAVED_BOTTOM_SHEET_PEEK_HEIGHT
    bottomSheet.layoutParams.height = getDisplayHeight(context!!)
    if (savedInstanceState == null && homeViewModel.user.value == null)
        childFragmentManager.beginTransaction().replace(
                R.id.savedContentContainer,
                SignInDialogFragment.newInstance(Bundle().apply {
                    putInt(SIGNIN_TYPE_KEY, FULLSCREEN.code)
                }))
                .commit()
    bottomSheetBehavior.setBottomSheetCallback(object : BottomSheetBehavior.BottomSheetCallback() {
        override fun onStateChanged(bottomSheet: View, newState: Int) {
            if (newState == STATE_EXPANDED) {
                homeViewModel.bottomSheetState.value = STATE_EXPANDED
                setBottomSheetExpanded()
            }
            if (newState == STATE_COLLAPSED) {
                isSavedContentExpanded = false
                appBar.visibility = VISIBLE
                bottom_handle.visibility = VISIBLE
                bottom_handle_elevation.visibility = VISIBLE
            }
        }

        override fun onSlide(bottomSheet: View, slideOffset: Float) {}
    })
    ...
}

private fun setBottomSheetExpanded() {
    isSavedContentExpanded = true
    appBar.visibility = GONE
    bottom_handle.visibility = GONE
    bottom_handle_elevation.visibility = GONE
}

private fun initSavedContentFragment() {
    childFragmentManager.beginTransaction().replace(
            savedContentContainer.id,
            ContentFragment.newInstance(Bundle().apply { putString(FEED_TYPE_KEY, SAVED.name) }),
            SAVED_CONTENT_TAG).commit()
}

...

private fun observeSignIn(savedInstanceState: Bundle?) {
    homeViewModel.user.observe(this, Observer { user: FirebaseUser? ->
        this.user = user
        ...
        if (user != null) { // Signed in.
            ...
            if (savedInstanceState == null || savedInstanceState.getParcelable<FirebaseUser>(USER_KEY) == null) {
                initMainContent()
                initSavedContentFragment()
            }
        } else if (savedInstanceState == null)  /*Signed out.*/ initMainContent()
    })
}

private fun initMainContent() {
    (childFragmentManager.findFragmentById(R.id.contentContainer) as ContentFragment)
            .initMainContent(false)
}

fun initSwipeToRefresh() {
    homeViewModel.isSwipeToRefreshEnabled.observe(viewLifecycleOwner, Observer { isEnabled: Boolean ->
        ...
        (childFragmentManager.findFragmentById(R.id.priceContainer) as PriceFragment)
                .getPrices(false, false)
        if (homeViewModel.accountType.value == FREE) updateAds()
    }
}

private fun updateAds() {
    (childFragmentManager.findFragmentById(R.id.contentContainer) as ContentFragment)
            .updateAds(true)
    if (childFragmentManager.findFragmentById(R.id.savedContentContainer) as ContentFragment != null)
        (childFragmentManager.findFragmentById(R.id.savedContentContainer) as ContentFragment)
                .updateAds(true)
}

...
}

Answer 1

作为保存RecyclerView状态的一种解决方法，可以将位置保存为实例状态。

override fun onSaveInstanceState(outState: Bundle) {
    super.onSaveInstanceState(outState)
    if (contentRecyclerView != null)
        when (feedType) {
            MAIN.name, DISMISSED.name ->
                outState.putParcelable(CONTENT_RECYCLER_VIEW_STATE,
                        contentRecyclerView.layoutManager!!.onSaveInstanceState())
            SAVED.name ->
                outState.putInt(CONTENT_RECYCLER_VIEW_POSITION,
                        (contentRecyclerView.layoutManager as LinearLayoutManager)
                                .findLastVisibleItemPosition())
        }
}

override fun onViewStateRestored(savedInstanceState: Bundle?) {
    super.onViewStateRestored(savedInstanceState)
    if (savedInstanceState != null)
        when (feedType) {
            MAIN.name, DISMISSED.name -> savedRecyclerLayoutState = savedInstanceState.getParcelable(CONTENT_RECYCLER_VIEW_STATE)
            SAVED.name -> savedRecyclerPosition = savedInstanceState.getInt(CONTENT_RECYCLER_VIEW_POSITION)
        }
}

为确保保存的索引没有超出范围，需要进行检查。此外，由于关闭了 RecyclerView 项目，因此清除已保存的索引位置很重要，这样在删除项目后不会更新 RecyclerView ，因为此代码段包含在LiveData观察者。

if (feedType == SAVED.name && savedRecyclerPosition != 0) {
                        val position: Int =
                                if (savedRecyclerPosition >= adapter.itemCount) adapter.itemCount - 1
                                else savedRecyclerPosition
                        contentRecyclerView.layoutManager?.scrollToPosition(position)
                        savedRecyclerPosition = 0
                    }

BottomSheet中的RecyclerView onRestoreInstanceState不起作用

预期

已观察

实施

1 个答案: