如何使用 Kotlin 在 ListAdapter 中使用 Filterable？

我会用一个SearchView过滤我的RecyclerView，在 stackoverflow 和其他网站上我发现只是使用的示例Filterable与 Java 和RecyclerView.Adapter当我使用时ListAdapter..

所以我试图自己制作自定义过滤器，但是当我尝试过滤适配器时，我只是得到一个空值MutableList in publishResults.

My Adapter代码如下所示：

class ArticoliListAdapter : ListAdapter<Articolo, ArticoliListAdapter.ArticoliViewHolder>(ArticoliComparator()), Filterable {
    private val list = mutableListOf<Articolo>()

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ArticoliViewHolder {
        return ArticoliViewHolder.create(parent)
    }

    override fun onBindViewHolder(holder: ArticoliViewHolder, position: Int) {
        val current = getItem(position)
        holder.bind(current)
    }

    override fun getItemId(position: Int): Long {
        val articolo = currentList[position]
        return articolo.barcode.hashCode().toLong()
    }




    class ArticoliViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
        private val barcode: TextView = itemView.findViewById(R.id.barcode)
        private val qta: TextView = itemView.findViewById(R.id.qta)
        private val desc: TextView = itemView.findViewById(R.id.desc)
        private val um: TextView = itemView.findViewById(R.id.um)
        fun bind(articolo: Articolo?) {
            barcode.text = articolo?.barcode
            qta.text = articolo?.qta?.formatForQta()
            um.text = articolo?.um?.toLowerCase(Locale.ITALIAN)
            desc.text = if(articolo?.desc.isNullOrEmpty()) "-" else articolo?.desc
        }

        private fun Float.formatForQta(): String {
            val floatString = this.toString()
            val decimalString: String = floatString.substring(floatString.indexOf('.') + 1, floatString.length)
            return when (decimalString.toInt() == 0) {
                true -> this.toInt().toString()
                false -> "%.3f".format(this)
            }
        }

        companion object {
            fun create(parent: ViewGroup): ArticoliViewHolder {
                val view: View = LayoutInflater.from(parent.context)
                    .inflate(R.layout.item_layout, parent, false)
                return ArticoliViewHolder(view)
            }
        }
    }

    class ArticoliComparator : DiffUtil.ItemCallback<Articolo>() {
        override fun areItemsTheSame(oldItem: Articolo, newItem: Articolo): Boolean {
            return oldItem === newItem
        }

        override fun areContentsTheSame(oldItem: Articolo, newItem: Articolo): Boolean {
            return oldItem.qta == newItem.qta
        }
    }

    override fun getFilter(): Filter {
        return customFilter
    }

    private val customFilter = object: Filter() {
        override fun performFiltering(constraint: CharSequence?): FilterResults {
            val filteredList = mutableListOf<Articolo>()
            if (constraint == null || constraint.isEmpty()){
                filteredList.addAll(currentList)
            }else {
                val filterPattern = constraint.toString().toLowerCase(Locale.ITALIAN).trim { it <= ' ' }
                for (item in currentList) {
                    if (item.barcode.toLowerCase(Locale.ITALIAN).contains(filterPattern) || item.desc?.toLowerCase(
                            Locale.ITALIAN
                        )!!.contains(filterPattern)) {
                        filteredList.add(item)
                    }
                }
            }
            val results = FilterResults()
            results.values = filteredList
            return results
        }

        override fun publishResults(constraint: CharSequence?, filterResults: FilterResults?) {
            list.clear()
            list.addAll(filterResults?.values as MutableList<Articolo>)
            notifyDataSetChanged()
        }

    }

}

所以我想知道哪种方法是构建自定义过滤器以在 Kotlin 中使用 ListAdapter 来过滤 recyclerView 中的数据的正确方法。

我在片段中调用过滤器，如下所示：

    override fun onQueryTextChange(query: String?): Boolean {
        adapter.filter.filter(query)
        return false
    }

但是当我尝试过滤时什么也没发生，并且仍然显示所有项目......

数据至RecyclerView适配器是从我设置的ViewHolder数据是从数据库中获取的（LiveData<List<Articolo>>)

这是我的片段中的代码：

   articoliViewModel.articoli.observe(viewLifecycleOwner) { articoli ->
        articoli.let { adapter.submitList(it) }
    }

我在下面列出的代码中几乎没有缺陷。

1. currentList正在保存列表中的当前项目，而不是完整的项目列表。即，如果您有 10 个项目，过滤后您会得到 3 个项目，那么currentList将持有 3 件物品而不是 10 件。所以你不能使用currentList用于过滤列表。相反，你坚持CompleteList并对这个应用过滤器。

2. 你不应该打电话notifyDataSetChanged()这完全违背了拥有的全部目的DiffUtils，而不是你打电话#submitList

3. Al 认为您有一个对完整列表作为全局变量的引用，但您从未为其赋值，它始终为空。

我制作了一个工作示例来说明。请尝试在您的代码中添加以下基本代码。我的使用类型为String只是为了使示例易于理解，您可以使用自定义对象。您还可以修改代码以使其看起来更好，但我认为它足以了解如何ListAdapter works.

class ArticoliListAdapter : ListAdapter<String, ArticoliListAdapter.ArticoliViewHolder>(ArticoliComparator()), Filterable {
    private var list = mutableListOf<String>()

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ArticoliViewHolder {
        return ArticoliViewHolder.create(parent)
    }

    override fun onBindViewHolder(holder: ArticoliViewHolder, position: Int) {
        val current = getItem(position)
        holder.bind(current)
    }

    fun setData(list: MutableList<String>?){
        this.list = list!!
        submitList(list)
    }

    class ArticoliViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
        private val desc: TextView = itemView.findViewById(R.id.txtName)
        fun bind(name: String) {
            desc.text = name.toUpperCase()
        }

        companion object {
            fun create(parent: ViewGroup): ArticoliViewHolder {
                val view: View = LayoutInflater.from(parent.context)
                    .inflate(R.layout.item_list, parent, false)
                return ArticoliViewHolder(view)
            }
        }
    }

    class ArticoliComparator : DiffUtil.ItemCallback<String>() {
        override fun areItemsTheSame(oldItem: String, newItem: String): Boolean {
            return oldItem === newItem
        }

        override fun areContentsTheSame(oldItem: String, newItem: String): Boolean {
            return oldItem == newItem
        }
    }

    override fun getFilter(): Filter {
        return customFilter
    }

    private val customFilter = object : Filter() {
        override fun performFiltering(constraint: CharSequence?): FilterResults {
            val filteredList = mutableListOf<String>()
            if (constraint == null || constraint.isEmpty()) {
                filteredList.addAll(list)
            } else {
                for (item in list) {
                    if (item.toLowerCase().startsWith(constraint.toString().toLowerCase())) {
                        filteredList.add(item)
                    }
                }
            }
            val results = FilterResults()
            results.values = filteredList
            return results
        }

        override fun publishResults(constraint: CharSequence?, filterResults: FilterResults?) {
            submitList(filterResults?.values as MutableList<String>)
        }

    }
}

当您将数据设置为适配器时，您会调用setData not submitList.

articoliViewModel.articoli.observe(viewLifecycleOwner) { articoli ->
    articoli.let { adapter.setData(it) }
}