Android 如何将SQLite数据与可重用的RecyclerView适配器一起使用

我希望使用在

片段中声明的一些数据，以便将其显示为
RecyclerView
项。问题在于
myList
，我知道存在类型不匹配。但是，我在片段的
onCreateView
方法中创建了数据库表行，因为我希望对将来的数据集使用相同的
DatabaseHandler
。是否有一种可能的方法来使用片段中的这些行，同时确保数据可以通过项目类属性
fullName
和/或
缩写
进行过滤？我想避免为我将要创建的每个数据集创建一个新的
数据库处理程序

类型不匹配|必需：可变列表|找到：DatabaseHandler

项目类别

data class Companies (val id: Int, val fullName: String, val abbreviation: String)

class MyFragment : androidx.fragment.app.Fragment() {
    private var mAdapter: MyListAdapter? = null

    private lateinit var mRecyclerView: androidx.recyclerview.widget.RecyclerView

    private var mTwoPane: Boolean = false

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

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        val view = inflater.inflate(R.layout.layout_recyclerview, container, false)
        mTwoPane = (activity as androidx.fragment.app.FragmentActivity).findViewById<View>(R.id.detail_container) != null

        mRecyclerView = view.findViewById<RecyclerView>(R.id.recyclerView_list)
        mRecyclerView.setHasFixedSize(true)
        mRecyclerView.layoutManager = androidx.recyclerview.widget.LinearLayoutManager(this.activity)
        mRecyclerView.addItemDecoration(androidx.recyclerview.widget.DividerItemDecoration(Objects.requireNonNull<Context>(context), LinearLayout.VERTICAL))

        val companyA = Companies(1, "GlaxoSmithKline plc", "GSK")
        val companyB = Companies(2, "Hiscox Ltd", "HSX")
        val companyC = Companies(3, "InterContinental Hotels Group plc", "IHG")
        val companyD = Companies(4, "Marks & Spencer Group plc", "MKS")
        val companyE = Companies(5, "FTSE 150", "")
        val companyF = Companies(6, "FTSE 250", "")

        val myList = DatabaseHandler(this.context!!)
        myList.insertData(companyA)
        myList.insertData(companyB)
        myList.insertData(companyC)
        myList.insertData(companyD)
        myList.insertData(companyE)
        myList.insertData(companyF)

        mRecyclerView.adapter = mAdapter

        mAdapter = MyListAdapter(activity!!, myList, mTwoPane)
        return view
    }

    override fun onCreateOptionsMenu(menu: Menu, inflater: MenuInflater) {
        val mInflater = Objects.requireNonNull<androidx.fragment.app.FragmentActivity>(activity).menuInflater
        mInflater.inflate(R.menu.menu_search, menu)

        val searchitem = menu.findItem(R.id.action_search)
        val searchView = searchitem.actionView as SearchView
        searchView.maxWidth = Integer.MAX_VALUE

        searchView.queryHint = Objects.requireNonNull<Context>(context).getText(R.string.searchhint_stopname)

        searchView.setOnQueryTextListener(object : SearchView.OnQueryTextListener {
            override fun onQueryTextSubmit(query: String): Boolean {
                return false
            }

            override fun onQueryTextChange(newText: String): Boolean {
                mAdapter!!.filter.filter(newText)
                return false
            }
        })

        super.onCreateOptionsMenu(menu, inflater)
    }
}

class DatabaseHandler(context: Context) : SQLiteOpenHelper(context, DatabaseHandler.DB_NAME, null, DatabaseHandler.DB_VERSION) {
    override fun onCreate(db: SQLiteDatabase) {
        val createTable = "CREATE TABLE $TABLE_NAME ($COL_ID INTEGER PRIMARY KEY, $COL_NAME TEXT, $COL_ABBREVIATION TEXT);"
        db.execSQL(createTable)
    }

    override fun onUpgrade(db: SQLiteDatabase, oldVersion: Int, newVersion: Int) {
        val dropTable = "DROP TABLE IF EXISTS $TABLE_NAME"
        db.execSQL(dropTable)
        onCreate(db)
    }

    fun insertData(companies: Companies): Boolean {
        val db = this.readableDatabase
        val values = ContentValues()
        values.put(COL_ID, companies.id)
        values.put(COL_NAME, companies.fullName)
        values.put(COL_ABBREVIATION, companies.abbreviation)

        val _success = db.insert(TABLE_NAME, null, values)
        db.close()

        Log.v("Insertion complete", "Record Inserted Successfully")

        return (Integer.parseInt("$_success") != -1)
    }

    fun getCompany(_id: Int): Companies {
        val companies = Companies(_id, "", "")
        val db = writableDatabase
        val selectQuery = "SELECT * FROM $TABLE_NAME WHCOL_$COL_ID = $_id"
        val cursor = db.rawQuery(selectQuery, null)
        if (cursor != null) {
            cursor.moveToFirst()
            while (cursor.moveToNext()) {
                val id = Integer.parseInt(cursor.getString(cursor.getColumnIndex(COL_ID)))
                val fullName = cursor.getString(cursor.getColumnIndex(COL_NAME))
                val abbreviation = cursor.getString(cursor.getColumnIndex(COL_ABBREVIATION))
            }
        }
        cursor.close()
        return companies
    }

    companion object {
        private const val DB_VERSION = 1
        private const val DB_NAME = "MyCompanies"
        private const val TABLE_NAME = "Companies"
        private const val COL_ID = "Id"
        private const val COL_NAME = "Name"
        private const val COL_ABBREVIATION = "Abbreviation"
    }
}

class MyListAdapter(private val mCtx: Context, 
                    private val myList: MutableList<Companies>,
                    private val mTwoPane: Boolean) : androidx.recyclerview.widget.RecyclerView.Adapter<MyListAdapter.CompanyViewHolder>(), Filterable {
    private var myListFull = myList.toMutableList()

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

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

                    for (item in myListFull) {
                        when {
                            item.companyName!!.toLowerCase().contains(filterPattern) ->
                                filteredList.add(item)
                        }
                    }
                }
            }

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

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

    inner class CompanyViewHolder(itemView: View) : androidx.recyclerview.widget.RecyclerView
    .ViewHolder(itemView) {
        var tvTitle: TextView = itemView.findViewById(R.id.tv_RVItem)
    }

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

    override fun onBindViewHolder(holder: CompanyViewHolder, position: Int) {
        val product = myList[holder.adapterPosition]

        holder.tvTitle.text = product.companyfuName
    }

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

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

片段类

data class Companies (val id: Int, val fullName: String, val abbreviation: String)

class MyFragment : androidx.fragment.app.Fragment() {
    private var mAdapter: MyListAdapter? = null

    private lateinit var mRecyclerView: androidx.recyclerview.widget.RecyclerView

    private var mTwoPane: Boolean = false

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

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        val view = inflater.inflate(R.layout.layout_recyclerview, container, false)
        mTwoPane = (activity as androidx.fragment.app.FragmentActivity).findViewById<View>(R.id.detail_container) != null

        mRecyclerView = view.findViewById<RecyclerView>(R.id.recyclerView_list)
        mRecyclerView.setHasFixedSize(true)
        mRecyclerView.layoutManager = androidx.recyclerview.widget.LinearLayoutManager(this.activity)
        mRecyclerView.addItemDecoration(androidx.recyclerview.widget.DividerItemDecoration(Objects.requireNonNull<Context>(context), LinearLayout.VERTICAL))

        val companyA = Companies(1, "GlaxoSmithKline plc", "GSK")
        val companyB = Companies(2, "Hiscox Ltd", "HSX")
        val companyC = Companies(3, "InterContinental Hotels Group plc", "IHG")
        val companyD = Companies(4, "Marks & Spencer Group plc", "MKS")
        val companyE = Companies(5, "FTSE 150", "")
        val companyF = Companies(6, "FTSE 250", "")

        val myList = DatabaseHandler(this.context!!)
        myList.insertData(companyA)
        myList.insertData(companyB)
        myList.insertData(companyC)
        myList.insertData(companyD)
        myList.insertData(companyE)
        myList.insertData(companyF)

        mRecyclerView.adapter = mAdapter

        mAdapter = MyListAdapter(activity!!, myList, mTwoPane)
        return view
    }

    override fun onCreateOptionsMenu(menu: Menu, inflater: MenuInflater) {
        val mInflater = Objects.requireNonNull<androidx.fragment.app.FragmentActivity>(activity).menuInflater
        mInflater.inflate(R.menu.menu_search, menu)

        val searchitem = menu.findItem(R.id.action_search)
        val searchView = searchitem.actionView as SearchView
        searchView.maxWidth = Integer.MAX_VALUE

        searchView.queryHint = Objects.requireNonNull<Context>(context).getText(R.string.searchhint_stopname)

        searchView.setOnQueryTextListener(object : SearchView.OnQueryTextListener {
            override fun onQueryTextSubmit(query: String): Boolean {
                return false
            }

            override fun onQueryTextChange(newText: String): Boolean {
                mAdapter!!.filter.filter(newText)
                return false
            }
        })

        super.onCreateOptionsMenu(menu, inflater)
    }
}

class DatabaseHandler(context: Context) : SQLiteOpenHelper(context, DatabaseHandler.DB_NAME, null, DatabaseHandler.DB_VERSION) {
    override fun onCreate(db: SQLiteDatabase) {
        val createTable = "CREATE TABLE $TABLE_NAME ($COL_ID INTEGER PRIMARY KEY, $COL_NAME TEXT, $COL_ABBREVIATION TEXT);"
        db.execSQL(createTable)
    }

    override fun onUpgrade(db: SQLiteDatabase, oldVersion: Int, newVersion: Int) {
        val dropTable = "DROP TABLE IF EXISTS $TABLE_NAME"
        db.execSQL(dropTable)
        onCreate(db)
    }

    fun insertData(companies: Companies): Boolean {
        val db = this.readableDatabase
        val values = ContentValues()
        values.put(COL_ID, companies.id)
        values.put(COL_NAME, companies.fullName)
        values.put(COL_ABBREVIATION, companies.abbreviation)

        val _success = db.insert(TABLE_NAME, null, values)
        db.close()

        Log.v("Insertion complete", "Record Inserted Successfully")

        return (Integer.parseInt("$_success") != -1)
    }

    fun getCompany(_id: Int): Companies {
        val companies = Companies(_id, "", "")
        val db = writableDatabase
        val selectQuery = "SELECT * FROM $TABLE_NAME WHCOL_$COL_ID = $_id"
        val cursor = db.rawQuery(selectQuery, null)
        if (cursor != null) {
            cursor.moveToFirst()
            while (cursor.moveToNext()) {
                val id = Integer.parseInt(cursor.getString(cursor.getColumnIndex(COL_ID)))
                val fullName = cursor.getString(cursor.getColumnIndex(COL_NAME))
                val abbreviation = cursor.getString(cursor.getColumnIndex(COL_ABBREVIATION))
            }
        }
        cursor.close()
        return companies
    }

    companion object {
        private const val DB_VERSION = 1
        private const val DB_NAME = "MyCompanies"
        private const val TABLE_NAME = "Companies"
        private const val COL_ID = "Id"
        private const val COL_NAME = "Name"
        private const val COL_ABBREVIATION = "Abbreviation"
    }
}

class MyListAdapter(private val mCtx: Context, 
                    private val myList: MutableList<Companies>,
                    private val mTwoPane: Boolean) : androidx.recyclerview.widget.RecyclerView.Adapter<MyListAdapter.CompanyViewHolder>(), Filterable {
    private var myListFull = myList.toMutableList()

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

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

                    for (item in myListFull) {
                        when {
                            item.companyName!!.toLowerCase().contains(filterPattern) ->
                                filteredList.add(item)
                        }
                    }
                }
            }

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

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

    inner class CompanyViewHolder(itemView: View) : androidx.recyclerview.widget.RecyclerView
    .ViewHolder(itemView) {
        var tvTitle: TextView = itemView.findViewById(R.id.tv_RVItem)
    }

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

    override fun onBindViewHolder(holder: CompanyViewHolder, position: Int) {
        val product = myList[holder.adapterPosition]

        holder.tvTitle.text = product.companyfuName
    }

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

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

MyListAdapter类

data class Companies (val id: Int, val fullName: String, val abbreviation: String)

class MyFragment : androidx.fragment.app.Fragment() {
    private var mAdapter: MyListAdapter? = null

    private lateinit var mRecyclerView: androidx.recyclerview.widget.RecyclerView

    private var mTwoPane: Boolean = false

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

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        val view = inflater.inflate(R.layout.layout_recyclerview, container, false)
        mTwoPane = (activity as androidx.fragment.app.FragmentActivity).findViewById<View>(R.id.detail_container) != null

        mRecyclerView = view.findViewById<RecyclerView>(R.id.recyclerView_list)
        mRecyclerView.setHasFixedSize(true)
        mRecyclerView.layoutManager = androidx.recyclerview.widget.LinearLayoutManager(this.activity)
        mRecyclerView.addItemDecoration(androidx.recyclerview.widget.DividerItemDecoration(Objects.requireNonNull<Context>(context), LinearLayout.VERTICAL))

        val companyA = Companies(1, "GlaxoSmithKline plc", "GSK")
        val companyB = Companies(2, "Hiscox Ltd", "HSX")
        val companyC = Companies(3, "InterContinental Hotels Group plc", "IHG")
        val companyD = Companies(4, "Marks & Spencer Group plc", "MKS")
        val companyE = Companies(5, "FTSE 150", "")
        val companyF = Companies(6, "FTSE 250", "")

        val myList = DatabaseHandler(this.context!!)
        myList.insertData(companyA)
        myList.insertData(companyB)
        myList.insertData(companyC)
        myList.insertData(companyD)
        myList.insertData(companyE)
        myList.insertData(companyF)

        mRecyclerView.adapter = mAdapter

        mAdapter = MyListAdapter(activity!!, myList, mTwoPane)
        return view
    }

    override fun onCreateOptionsMenu(menu: Menu, inflater: MenuInflater) {
        val mInflater = Objects.requireNonNull<androidx.fragment.app.FragmentActivity>(activity).menuInflater
        mInflater.inflate(R.menu.menu_search, menu)

        val searchitem = menu.findItem(R.id.action_search)
        val searchView = searchitem.actionView as SearchView
        searchView.maxWidth = Integer.MAX_VALUE

        searchView.queryHint = Objects.requireNonNull<Context>(context).getText(R.string.searchhint_stopname)

        searchView.setOnQueryTextListener(object : SearchView.OnQueryTextListener {
            override fun onQueryTextSubmit(query: String): Boolean {
                return false
            }

            override fun onQueryTextChange(newText: String): Boolean {
                mAdapter!!.filter.filter(newText)
                return false
            }
        })

        super.onCreateOptionsMenu(menu, inflater)
    }
}

class DatabaseHandler(context: Context) : SQLiteOpenHelper(context, DatabaseHandler.DB_NAME, null, DatabaseHandler.DB_VERSION) {
    override fun onCreate(db: SQLiteDatabase) {
        val createTable = "CREATE TABLE $TABLE_NAME ($COL_ID INTEGER PRIMARY KEY, $COL_NAME TEXT, $COL_ABBREVIATION TEXT);"
        db.execSQL(createTable)
    }

    override fun onUpgrade(db: SQLiteDatabase, oldVersion: Int, newVersion: Int) {
        val dropTable = "DROP TABLE IF EXISTS $TABLE_NAME"
        db.execSQL(dropTable)
        onCreate(db)
    }

    fun insertData(companies: Companies): Boolean {
        val db = this.readableDatabase
        val values = ContentValues()
        values.put(COL_ID, companies.id)
        values.put(COL_NAME, companies.fullName)
        values.put(COL_ABBREVIATION, companies.abbreviation)

        val _success = db.insert(TABLE_NAME, null, values)
        db.close()

        Log.v("Insertion complete", "Record Inserted Successfully")

        return (Integer.parseInt("$_success") != -1)
    }

    fun getCompany(_id: Int): Companies {
        val companies = Companies(_id, "", "")
        val db = writableDatabase
        val selectQuery = "SELECT * FROM $TABLE_NAME WHCOL_$COL_ID = $_id"
        val cursor = db.rawQuery(selectQuery, null)
        if (cursor != null) {
            cursor.moveToFirst()
            while (cursor.moveToNext()) {
                val id = Integer.parseInt(cursor.getString(cursor.getColumnIndex(COL_ID)))
                val fullName = cursor.getString(cursor.getColumnIndex(COL_NAME))
                val abbreviation = cursor.getString(cursor.getColumnIndex(COL_ABBREVIATION))
            }
        }
        cursor.close()
        return companies
    }

    companion object {
        private const val DB_VERSION = 1
        private const val DB_NAME = "MyCompanies"
        private const val TABLE_NAME = "Companies"
        private const val COL_ID = "Id"
        private const val COL_NAME = "Name"
        private const val COL_ABBREVIATION = "Abbreviation"
    }
}

class MyListAdapter(private val mCtx: Context, 
                    private val myList: MutableList<Companies>,
                    private val mTwoPane: Boolean) : androidx.recyclerview.widget.RecyclerView.Adapter<MyListAdapter.CompanyViewHolder>(), Filterable {
    private var myListFull = myList.toMutableList()

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

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

                    for (item in myListFull) {
                        when {
                            item.companyName!!.toLowerCase().contains(filterPattern) ->
                                filteredList.add(item)
                        }
                    }
                }
            }

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

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

    inner class CompanyViewHolder(itemView: View) : androidx.recyclerview.widget.RecyclerView
    .ViewHolder(itemView) {
        var tvTitle: TextView = itemView.findViewById(R.id.tv_RVItem)
    }

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

    override fun onBindViewHolder(holder: CompanyViewHolder, position: Int) {
        val product = myList[holder.adapterPosition]

        holder.tvTitle.text = product.companyfuName
    }

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

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

class MyListAdapter（私有val mCtx:Context，
private val myList:MutableList，
private val mTwoPane:Boolean）：androidx.recyclerview.widget.recyclerview.Adapter（），可筛选{
私有变量myListFull=myList.toMutableList（）
private val companyFilter=object:Filter（）{
重写性能筛选（约束：CharSequence？）：Filter.FilterResults{
val filteredList=ArrayList（）
什么时候{
constraint==null | | constraint.isEmpty（）->filteredList.addAll（myListFull）
其他->{
val filterPattern=constraint.toString（）.toLowerCase（）.trim{it
filteredList.add（项目）
}
}
}
}
val results=Filter.FilterResults（）
results.values=filteredList
返回结果
}
覆盖有趣的publishResults（约束：CharSequence？，结果：Filter.FilterResults？）{
myList.clear（）
myList.addAll（结果！！.value作为列表）
notifyDataSetChanged（）
}
}
内部类CompanyViewHolder（itemView:View）：androidx.recyclerview.widget.recyclerview
.ViewHolder（项目视图）{
变量tvTitle:TextView=itemView.findViewById（R.id.tv\RVItem）
}
override fun onCreateViewHolder（父级：ViewGroup，viewType:Int）：CompanyViewHolder{
val充气机=充气机从（mCtx）
val v=充气机。充气（R.layout.recyclerview\u item\u textview，父项，false）
返回公司翼肩（v）
}
覆盖BindViewHolder（holder:CompanyViewHolder，position:Int）{
val product=myList[支架.适配器位置]
holder.tvTitle.text=product.companyfuName
}
重写getItemCount（）：Int{
返回myList.size
}
重写getFilter（）：筛选器{
返回公司过滤器
}
}

初始化
DatabaseHandler
使
getCompany
函数返回公司类型的列表或数组

将它交给适配器，以手动方式显示它
Java代码如下所示：

 // My recycler view 
 RecyclerView rv = (RecyclerView) findViewById(R.id.RVCategory);
 LinearLayoutManager llm = new LinearLayoutManager(this);
 rv.setLayoutManager(llm);

 // My data helper 
 MDBHelper mDBHelper = new DbHelper(this);

 // I gave the returned list to the list in the `Activity` 
 List = mDBHelper.GetCompany();

 // Then I gave it to the adapter
 Adapter_Category adapter = new Adapter_Category(CategoryList, inflater);
 rv.setAdapter(adapter);

请更具体地回答。你很快就把它打出来了，不容易理解。初始化
DatabaseHandler
where？你的意思是-在适配器中使用
private val myList:DatabaseHandler
？在活动中初始化DatabaseHandler，以便访问getCompany函数并获取返回的列表我没有使用活动，我使用的是片段。您的意思是类似于
val myList:DatabaseHandler
？我在片段中的onCreate之前添加了它；LinearLayoutManager llm=新的LinearLayoutManager（本）；rv.setLayoutManager（llm）；//我的数据helber MDBHelper MDBHelper=new DbHelper（this）；//将返回的列表保存到activity list=mDBHelper.GetCompany（）；//然后我把它交给adabter adabter_Category adapter=new adabter_Category（类别列表，充气器）；rv.设置适配器（适配器）；