RecyclerView 的空数据集指示器未显示

Question

我试图在过滤后的 RecyclerView 的数据集包含 0 个项目时显示带有消息的 Snackbar，但由于某种原因，Snackbar 根本没有出现。相关代码是否需要放到Fragment或Adapter中？没有图书馆可以吗？

class MyFragment : androidx.fragment.app.Fragment() {
    private lateinit var mRecyclerView: RecyclerView
    private var mAdapter: MyAdapter? = null
    private lateinit var mSearchView: SearchView
    private lateinit var mSearchMenuItem: MenuItem
    private val myList = ArrayList<Item>()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
    }

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

        mRecyclerView = view.findViewById(R.id.myRecyclerView)
        mRecyclerView.setHasFixedSize(true)
        mRecyclerView.layoutManager =
            androidx.recyclerview.widget.LinearLayoutManager(this.activity)
        mRecyclerView.addItemDecoration(
                androidx.recyclerview.widget.DividerItemDecoration(
                        context, LinearLayout.VERTICAL
                )
        )

        myList.add(
                Item(
                        getString(R.string.item_a)
                )
        )

        mAdapter = MyAdapter(requireActivity(), myList)

        mRecyclerView.adapter = mAdapter

        return view
    }

    override fun onCreateOptionsMenu(menu: Menu, inflater: MenuInflater) {
         val mSnackbar = Snackbar.make(
                requireView(),
                getString(R.string.no_items),
                Snackbar.LENGTH_LONG
        )
        
        mSearchView.setOnQueryTextListener(object : SearchView.OnQueryTextListener {
            override fun onQueryTextSubmit(query: String): Boolean {
                return false
            }

            override fun onQueryTextChange(newText: String): Boolean {
                mAdapter!!.filter.filter(newText)
                mAdapter!!.notifyDataSetChanged()

                if (mAdapter!!.itemCount <1) {
                    mSnackbar.show()
                } else {
                    mSnackbar.dismiss()
                }

                return false
            }
        })

        super.onCreateOptionsMenu(menu, inflater)
    }
}

适配器代码

class MyAdapter(
    private val mCtx: Context,
    var myList: MutableList<Item>,
) : androidx.recyclerview.widget.RecyclerView.Adapter<MyAdapter.MyViewHolder>(), Filterable {
    private val myListFull = myList.toMutableList()

val mSnackbar = Snackbar.make(
        requireView(),
        getString(R.string.my_message),
        Snackbar.LENGTH_INDEFINITE
)

    private val companyFilter = object : Filter() {
        override fun performFiltering(constraint: CharSequence?): FilterResults {
            val filteredList = ArrayList<Item>()

            if (constraint == null || constraint.isEmpty()) {
                filteredList.addAll(myListFull)
            } else {
                val filterPattern = constraint.toString().toLowerCase().trim { it <= ' ' }

                for (item in myListFull) {
                    if (item.Name.toLowerCase().contains(filterPattern)
                    ) {
                        filteredList.add(item)
                    }
                }
            }

            val results = FilterResults()
            results.values = filteredList
            return results
        }

        override fun publishResults(constraint: CharSequence?, results: FilterResults?) {
            myList.clear()
            myList.addAll(results!!.values as List<Item>)
            notifyDataSetChanged()

        if (filteredList.isEmpty()) {
            mSnackbar.show()
        } else {
            mSnackbar.dismiss()
        }

        }
    }

    private fun String.matchesIgnoreCase(otherString: String): Boolean {
        return this.toLowerCase().contains(otherString.trim().toLowerCase())
    }

    class MyViewHolder(itemView: View) : androidx.recyclerview.widget.RecyclerView
    .ViewHolder(itemView) {
        var tvTitle: TextView = itemView.findViewById(R.id.title)
        var tvSubtitle: TextView = itemView.findViewById(R.id.subtitle)
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): MyViewHolder {
        val inflater = LayoutInflater.from(mCtx)
        val v = inflater.inflate(R.layout.list_item, parent, false)
        return MyViewHolder(v)
    }

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

    override fun getFilter(): Filter {
        return companyFilter
    }
}

Answer 1

我猜是 this:

Filtering operations performed by calling filter(java.lang.CharSequence) or filter(java.lang.CharSequence, android.widget.Filter.FilterListener) are performed asynchronously. When these methods are called, a filtering request is posted in a request queue and processed later.

因此您在调用 filter 后立即检查 myList（通过 getItemCount），并且数据尚未更新，因为过滤/发布内容尚未完成运行。所以你的小吃店被解雇了

publishResults 方法在 UI 线程上运行，所以如果需要，可以在那里显示快餐栏？

RecyclerView 的空数据集指示器未显示

Empty dataset indicator for RecyclerView not showing

android

android-adapter

kotlin

android-search

android-recyclerview