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法律研究如何在 Android 中使用 Kotlin 将 RecyclerView 与数据库结合使用？
此示例演示了如何在 Android 中使用 Kotlin 将 RecyclerView 与数据库结合使用。
步骤 1 − 在 Android Studio 中创建一个新项目，转到文件 ⇒ 新建项目，并填写所有必要信息以创建新项目。
步骤 2 − 将以下代码添加到 res/layout/activity_main.xml 中。
<?xml version="1.0" encoding="utf-8"?> <FrameLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" android:padding="4dp" tools:context=".MainActivity"> <androidx.recyclerview.widget.RecyclerView android:id="@+id/myContactList" android:layout_width="match_parent" android:layout_height="match_parent" android:layout_marginBottom="50dp" android:paddingBottom="8dp" /> <Button android:id="@+id/btnAdd" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_gravity="bottom|end" android:layout_marginEnd="16dp" android:layout_marginBottom="4dp" android:padding="2dp" android:text="ADD" /> </FrameLayout>
步骤 3 − 将以下代码添加到 src/MainActivity.kt 中。
import android.os.Bundle
import android.text.TextUtils
import android.view.LayoutInflater
import android.view.View
import android.widget.Button
import android.widget.EditText
import android.widget.Toast
import androidx.appcompat.app.AlertDialog
import androidx.appcompat.app.AppCompatActivity
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.RecyclerView
class MainActivity : AppCompatActivity() {
private lateinit var dataBase: SqliteDatabase
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
title = "KotlinApp"
val contactView: RecyclerView = findViewById(R.id.myContactList)
val linearLayoutManager = LinearLayoutManager(this)
contactView.layoutManager = linearLayoutManager
contactView.setHasFixedSize(true)
dataBase = SqliteDatabase(<Contacts>= dataBase.listContacts()
if (allContacts.size > 0) {
contactView.visibility = View.VISIBLE
val mAdapter = ContactAdapter(this, allContacts)
contactView.adapter = mAdapter
}
else {
contactView.visibility = View.GONE
Toast.makeText(
this,
"There is no contact in the database. Start adding now",
Toast.LENGTH_LONG
).show()
}
val btnAdd: Button = findViewById(R.id.btnAdd)
btnAdd.setOnClickListener { addTaskDialog() }
}
private fun addTaskDialog() {
val inflater = LayoutInflater.from(this)
val subView = inflater.inflate(R.layout.add_contacts, null)
val nameField: EditText = subView.findViewById(R.id.enterName)
val noField: EditText = subView.findViewById(R.id.enterPhoneNum)
val builder = AlertDialog.Builder(this)
builder.setTitle("Add new CONTACT")
builder.setView(subView)
builder.create()
builder.setPositiveButton("ADD CONTACT") { _, _ ->
val name = nameField.text.toString()
val phoneNum = noField.text.toString()
if (TextUtils.isEmpty(name)) {
Toast.makeText(
this@MainActivity,
"Something went wrong. Check your input values",
Toast.LENGTH_LONG
).show()
}
else {
val newContact = Contacts(name, phoneNum)
dataBase.addContacts(newContact)
finish()
startActivity(intent)
}
}
builder.setNegativeButton("CANCEL") { _, _ -> Toast.makeText(this@MainActivity, "Task cancelled",
Toast.LENGTH_LONG).show()}
builder.show()
}
override fun onDestroy() {
super.onDestroy()
dataBase.close()
}
}步骤 4 − 创建如下所述的 Kotlin 类文件并添加相应的代码
Contacts.kt −
class Contacts {
var id = 0
var name: String
var phno: String
internal constructor(name: String, phno: String) {
this.name = name
this.phno = phno
}
internal constructor(id: Int, name: String, phno: String) {
this.id = id
this.name = name
this.phno = phno
}
}ContactViewHolder.kt −
import android.view.View
import android.widget.ImageView
import android.widget.TextView
import androidx.recyclerview.widget.RecyclerView
class ContactViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
var tvName: TextView = itemView.findViewById(R.id.contactName)
var tvPhoneNum: TextView = itemView.findViewById(R.id.phoneNum)
var deleteContact: ImageView = itemView.findViewById(R.id.deleteContact)
var editContact: ImageView = itemView.findViewById(R.id.editContact)
}ContactAdapter.kt −
import android.app.Activity
import android.content.Context
import android.text.TextUtils
import android.view.LayoutInflater
import android.view.ViewGroup
import android.widget.EditText
import android.widget.Filter
import android.widget.Filterable
import android.widget.Toast
import androidx.appcompat.app.AlertDialog
import androidx.recyclerview.widget.RecyclerView
import java.util.*
internal class ContactAdapter(private val context: Context, listContacts: ArrayList<Contacts>) :
RecyclerView.Adapter<ContactViewHolder>(), Filterable {
private var listContacts: ArrayList<Contacts>
private val mArrayList: ArrayList<Contacts>
private val mDatabase: SqliteDatabase
init {
this.listContacts = listContacts
this.mArrayList = listContacts
mDatabase = SqliteDatabase(context)
}
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ContactViewHolder {
val view =
LayoutInflater.from(parent.context).inflate(R.layout.contact_list_layout, parent, false)
return ContactViewHolder(view)
}
override fun onBindViewHolder(holder: ContactViewHolder, position: Int) {
val contacts = listContacts[position]
holder.tvName.text = contacts.name
holder.tvPhoneNum.text = contacts.phno
holder.editContact.setOnClickListener { editTaskDialog(contacts) }
holder.deleteContact.setOnClickListener {
mDatabase.deleteContact(contacts.id)
(context as Activity).finish()
context.startActivity(context.intent)
}
}
override fun getFilter(): Filter {
return object : Filter() {
override fun performFiltering(charSequence: CharSequence): FilterResults {
val charString = charSequence.toString()
listContacts = if (charString.isEmpty()) {
mArrayList
}
else {
val filteredList = ArrayList<Contacts>()
for (contacts in mArrayList) {
if (contacts.name.toLowerCase().contains(charString)) {
filteredList.add(contacts)
}
}
filteredList
}
val filterResults = FilterResults()
filterResults.values = listContacts
return filterResults
}
override fun publishResults(
charSequence: CharSequence,
filterResults: FilterResults
)
{
listContacts =
filterResults.values as ArrayList<Contacts>
notifyDataSetChanged()
}
}
}
override fun getItemCount(): Int {
return listContacts.size
}
private fun editTaskDialog(contacts: Contacts) {
val inflater = LayoutInflater.from(context)
val subView = inflater.inflate(R.layout.add_contacts, null)
val nameField: EditText = subView.findViewById(R.id.enterName)
val contactField: EditText = subView.findViewById(R.id.enterPhoneNum)
nameField.setText(contacts.name)
contactField.setText(contacts.phno)
val builder = AlertDialog.Builder(context)
builder.setTitle("Edit contact")
builder.setView(subView)
builder.create()
builder.setPositiveButton(
"EDIT CONTACT"
) { _, _ ->
val name = nameField.text.toString()
val phNo = contactField.text.toString()
if (TextUtils.isEmpty(name)) {
Toast.makeText(
context,
"Something went wrong. Check your input values",
Toast.LENGTH_LONG
).show()
}
else {
mDatabase.updateContacts(
Contacts(
Objects.requireNonNull<Any>(contacts.id) as Int,
name,
phNo
)
)
(context as Activity).finish()
context.startActivity(context.intent)
}
}
builder.setNegativeButton(
"CANCEL"
) { _, _ -> Toast.makeText(context, "Task cancelled", Toast.LENGTH_LONG).show() }
builder.show()
}
}SqliteDatabase.kt −
import android.content.ContentValues
import android.content.Context
import android.database.sqlite.SQLiteDatabase
import android.database.sqlite.SQLiteOpenHelper
import java.util.*
class SqliteDatabase internal constructor(context: Context?) :
SQLiteOpenHelper(
context,
DATABASE_NAME,
null,
DATABASE_VERSION
) {
override fun onCreate(db: SQLiteDatabase) {
val createContactTable = ("CREATE TABLE "
+ TABLE_CONTACTS + "(" + COLUMN_ID
+ " INTEGER PRIMARY KEY,"
+ COLUMN_NAME + " TEXT,"
+ COLUMN_NO + " INTEGER" + ")")
db.execSQL(createContactTable)
}
override fun onUpgrade(
db: SQLiteDatabase,
oldVersion: Int,
newVersion: Int
) {
db.execSQL("DROP TABLE IF EXISTS $TABLE_CONTACTS")
onCreate(db)
}
fun listContacts(): ArrayList<Contacts> {
val sql = "select * from $TABLE_CONTACTS"
val db = this.readableDatabase
val storeContacts =
ArrayList<Contacts>()
val cursor = db.rawQuery(sql, null)
if (cursor.moveToFirst()) {
do {
val id = cursor.getString(0).toInt()
val name = cursor.getString(1)
val phno = cursor.getString(2)
storeContacts.add(Contacts(id, name, phno))
}
while (cursor.moveToNext())
}
cursor.close()
return storeContacts
}
fun addContacts(contacts: Contacts) {
val values = ContentValues()
values.put(COLUMN_NAME, contacts.name)
values.put(COLUMN_NO, contacts.phno)
val db = this.writableDatabase
db.insert(TABLE_CONTACTS, null, values)
}
fun updateContacts(contacts: Contacts) {
val values = ContentValues()
values.put(COLUMN_NAME, contacts.name)
values.put(COLUMN_NO, contacts.phno)
val db = this.writableDatabase
db.update(
TABLE_CONTACTS,
values,
"$COLUMN_ID = ?",
arrayOf(contacts.id.toString())
)
}
fun deleteContact(id: Int) {
val db = this.writableDatabase
db.delete(
TABLE_CONTACTS,
"$COLUMN_ID = ?",
arrayOf(id.toString())
)
}
companion object {
private const val DATABASE_VERSION = 5
private const val DATABASE_NAME = "Contacts"
private const val TABLE_CONTACTS = "Contacts"
private const val COLUMN_ID = "_id"
private const val COLUMN_NAME = "contactName"
private const val COLUMN_NO = "phoneNumber"
}
}步骤 5 − 创建布局资源文件（add_contacts.xml & contact_list_layout.xml）并添加以下代码
add_contacts.xml −
<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical"> <EditText android:id="@+id/enterName" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_marginEnd="8dp" android:hint="Enter Name" android:inputType="text" android:maxLines="1" android:padding="12dp" android:textSize="12dp" /> <EditText android:id="@+id/enterPhoneNum" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_marginTop="10dp" android:layout_marginEnd="8dp" android:hint="Enter Number" android:inputType="phone" android:maxLines="1" android:padding="12dp" android:textSize="12sp" /> </LinearLayout>
contact_list_layout.xml −
<?xml version="1.0" encoding="utf-8"?> <androidx.cardview.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_marginBottom="1dp" android:orientation="vertical"> <LinearLayout android:layout_width="match_parent" android:layout_height="wrap_content" android:orientation="horizontal" android:padding="12dp"> <RelativeLayout android:layout_width="wrap_content" android:layout_height="wrap_content"> <TextView android:id="@+id/contactName" android:layout_width="220dp" android:layout_height="wrap_content" android:textSize="12sp" android:textStyle="bold" /> <TextView android:id="@+id/phoneNum" android:layout_width="220dp" android:layout_height="wrap_content" android:layout_below="@+id/contactName" android:textSize="12sp" android:textStyle="bold" /> </RelativeLayout> <ImageView android:id="@+id/editContact" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_gravity="center_vertical" android:layout_weight="1" android:contentDescription="TODO" android:src="@drawable/ic_baseline_edit_24" /> <ImageView android:id="@+id/deleteContact" android:layout_width="0dp" android:layout_height="wrap_content" android:layout_gravity="center" android:layout_weight="1" android:contentDescription="TODO" android:src="@drawable/ic_baseline_remove_24" /> </LinearLayout> </androidx.cardview.widget.CardView>
步骤 6 − 将以下代码添加到 androidManifest.xml 中
<?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.example.q11"> <application android:allowBackup="true" android:icon="@mipmap/ic_launcher" android:label="@string/app_name" android:roundIcon="@mipmap/ic_launcher_round" android:supportsRtl="true" android:theme="@style/AppTheme"> <activity android:name=".MainActivity"> <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> </application> </manifest>
让我们尝试运行您的应用程序。我假设您已将您的实际 Android 移动设备连接到您的计算机。要从 Android Studio 运行应用程序，请打开项目的某个活动文件，然后单击工具栏中的运行 
图标。选择您的移动设备作为选项，然后检查您的移动设备，它将显示您的默认屏幕。
更新于： 2020 年 8 月 18 日
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