Android：LoadStateAdapter 不在 recyclerview 网格布局中居中

Question

我当前的问题是，我的LoadStateAdapter 显示加载和错误状态，不在我的recyclerview 内，它有一个网格布局作为布局管理器。我在官方的 android 开发者网站上没有找到任何关于此的信息，所以我在这里问：如何将我的 LoadStateAdapter 居中在我的 Recyclerview 中？

当前

片段

@AndroidEntryPoint
class ShopFragment : Fragment(R.layout.fragment_shop), ShopAdapter.OnItemClickListener {
    private val shopViewModel: ShopViewModel by viewModels()
    private val shopBinding: FragmentShopBinding by viewBinding()
    @Inject lateinit var shopListAdapter: ShopAdapter

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

    private fun bindObjects() {
        shopBinding.adapter = shopListAdapter.withLoadStateFooter(ShopLoadAdapter(shopListAdapter::retry))
        shopListAdapter.clickHandler(this)
    }

    override fun onDestroyView() {
        requireView().findViewById<RecyclerView>(R.id.rv_shop).adapter = null
        super.onDestroyView()
    }
}

适配器

@FragmentScoped
class ShopLoadAdapter(private val retry: () -> Unit): LoadStateAdapter<ShopLoadAdapter.ShopLoadStateViewHolder>() {

    inner class ShopLoadStateViewHolder(private val binding: ShopLoadStateFooterBinding) : RecyclerView.ViewHolder(binding.root) {
        fun bind(loadState: LoadState) {
            with(binding) {
                shopLoadPb.isVisible = loadState is LoadState.Loading
                shopLoadMbtnRetry.isVisible = loadState is LoadState.Error
                shopLoadTvError.isVisible = loadState is LoadState.Error
            }
        }
    }

    override fun onBindViewHolder(holder: ShopLoadStateViewHolder, loadState: LoadState) = holder.bind(loadState)

    override fun onCreateViewHolder(parent: ViewGroup, loadState: LoadState): ShopLoadStateViewHolder {
        val layoutInflater = LayoutInflater.from(parent.context)
        val binding = ShopLoadStateFooterBinding.inflate(layoutInflater, parent, false)
        return ShopLoadStateViewHolder(binding).also {
            binding.shopLoadMbtnRetry.setOnClickListener { retry.invoke() }
        }
    }
}

布局.xml

<androidx.recyclerview.widget.RecyclerView
    android:id="@+id/rv_shop"
    android:layout_width="match_parent"
    android:layout_height="0dp"
    android:layout_marginStart="8dp"
    android:layout_marginEnd="8dp"
    app:layoutManager="androidx.recyclerview.widget.GridLayoutManager"
    app:spanCount="2"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/headline"
    app:recyclerview_adapter="@{adapter}"
    tools:listitem="@layout/shop_list_item"/>

Answer 1

如果您使用“withLoadStateFooter”，请尝试此代码。 source

val footerAdapter = MainLoadStateAdapter(adapter)
recyclerView.adapter = adapter.withLoadStateFooter(footer = footerAdapter)
gridLayoutManager.spanSizeLookup =  object : GridLayoutManager.SpanSizeLookup() {
        override fun getSpanSize(position: Int): Int {
            return if (position == adapter.itemCount  && footerAdapter.itemCount > 0) {
                2
            } else {
                1
            }
        }
    }

Answer 2

首先，您必须在 PagingDataAdapter 中创建多种视图类型 之后覆盖 getItemViewType 方法，如下所示

// Define Loading ViewType
public static final int LOADING_ITEM = 0;
// Define Movie ViewType
public static final int MOVIE_ITEM = 1;

@Override
public int getItemViewType(int position) {
    // set ViewType
    return position == getItemCount() ? MOVIE_ITEM : LOADING_ITEM;
}

然后动态设置跨度大小

// set Grid span
    gridLayoutManager.setSpanSizeLookup(new GridLayoutManager.SpanSizeLookup() {
        @Override
        public int getSpanSize(int position) {
            // If progress will be shown then span size will be 1 otherwise it will be 2
            return moviesAdapter.getItemViewType(position) == MoviesAdapter.LOADING_ITEM ? 1 : 2;
        }
    });

您可以查看此paging 3 example，其中包括在中心显示加载状态视图

Answer 3

在谷歌搜索您的问题后，我发现this anwser 与spanSizeLookup 有关。 首先我们创建一个GridLayoutManager 的实例并将其添加到RecyclerView

    // Create a grid layout with two columns
    val adapter = ShopLoadAdapter(yourItems)
    val layoutManager = GridLayoutManager(context, 2)

    // Create a custom SpanSizeLookup where the first item spans both columns
    layoutManager.spanSizeLookup = object : SpanSizeLookup() {
        override fun getSpanSize(position: Int): Int {
            return if (adapter.getItemViewType(position) == ShopLoadAdapter.ERROR_RETRY) 2 else 1
        }
    }

    val recyclerView = findViewById<RecyclerView>(R.id.recyclerview)
    recyclerView.layoutManager = layoutManager
    recyclerView.adapter = adapter

我们必须创建两个不同的ViewHolders，因为我们要显示两个不同的布局。

class ViewHolderA(view: View) : RecyclerView.ViewHolder(view) {
    var image: ImageView = view.findViewById(R.id.image)
    //initialize your views for your items
}

class ViewHolderB(view: View) : RecyclerView.ViewHolder(view) {
    val button: Button = view.findViewById(R.id.retry_button)
    //initalize your views for the retry item
}

ShopLoadAdapter 应如下所示：

class ShopLoadAdapter(private val items: ArrayList<Item>) : RecyclerView.Adapter<RecyclerView.ViewHolder>() {

    val NORMAL_ITEM = 0
    val ERROR_RETRY = 1

    override fun onCreateViewHolder(viewGroup: ViewGroup, viewType: Int): RecyclerView.ViewHolder {
        val view: View

        if(viewType == ShopLoadAdapter.NORMAL_ITEM){
            view = LayoutInflater.from(viewGroup.context)
                    .inflate(R.layout.normal_item, viewGroup, false)
            return ViewHolderA(view)
        }

        view = LayoutInflater.from(viewGroup.context)
                .inflate(R.layout.error_retry_item, viewGroup, false)
        return ViewHolderB(view)
    }

    override fun onBindViewHolder(viewHolder: RecyclerView.ViewHolder, i: Int)     {
        // Bind your items using i as position
    }

    override fun getItemViewType(position: Int): Int {
        return when {
            items[position].hasError -> 1
            else -> 0
        }
    }

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

Answer 4

如果您还有用于刷新状态的 loadStateAdapter，请使用此选项。

gridLayoutManager.spanSizeLookup = object : GridLayoutManager.SpanSizeLookup() {
        override fun getSpanSize(position: Int): Int {
            return if ((position == adapter.itemCount) && footerAdapter.itemCount > 0) {
                spanCount
            } else if (adapter.itemCount == 0 && headerAdapter.itemCount > 0) {
                spanCount
            } else {
                1
            }
        }
    }