Cách làm nổi bật mục được chọn trong Android RecyclerView bằng Kotlin đúng cách

Ví dụ này minh họa cách làm nổi bật đúng các mục được chọn trong Android RecyclerView sử dụng Kotlin.

Bước 1: Tạo dự án mới

Trong Android Studio, chọn File → New Project và điền đầy đủ thông tin cần thiết để tạo dự án mới.

Bước 2: Cấu hình layout chính (activity_main.xml)

Thêm mã sau vào res/layout/activity_main.xml:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="https://schemas.android.com/apk/res/android"
    xmlns:tools="https://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/recyclerView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:paddingBottom="8dp" />
</RelativeLayout>

Bước 3: Viết mã MainActivity.kt

Thêm mã sau vào src/MainActivity.kt:

import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.RecyclerView

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        title = "KotlinApp"
        
        val recyclerView: RecyclerView = findViewById(R.id.recyclerView)
        recyclerView.addItemDecoration(SimpleItemDecoration(this))
        
        val layoutManager = LinearLayoutManager(this@MainActivity)
        recyclerView.layoutManager = layoutManager
        
        val posts = returnListItems()
        val adapter = RecyclerViewAdapter(this@MainActivity, posts)
        recyclerView.adapter = adapter
    }
    
    private fun returnListItems(): List<ItemObject>? {
        val items: MutableList<ItemObject> = ArrayList()
        items.add(ItemObject("Ballon d'or", "2007", "Ricardo KaKa"))
        items.add(ItemObject("Ballon d'or", "2008", "Cristiano Ronaldo"))
        items.add(ItemObject("Ballon d'or", "2009 - 2012, 2015", "Lionel Messi"))
        items.add(ItemObject("Ballon d'or", "2013, 2014, 2016, 2017", "Cristiano Ronaldo"))
        items.add(ItemObject("Ballon d'or", "2018", "Luca Modric"))
        items.add(ItemObject("Ballon d'or", "2019", "Lionel Messi"))
        return items
    }
}

Bước 4: Tạo các lớp Kotlin cần thiết

ItemObject.kt

internal class ItemObject(
    val awardTitle: String,
    val awardYear: String,
    val player: String
)

RecyclerViewAdapter.kt

import android.view.LayoutInflater
import android.view.ViewGroup
import androidx.annotation.NonNull
import androidx.recyclerview.widget.RecyclerView

class RecyclerViewAdapter internal constructor(
    context: MainActivity,
    private val itemList: List<ItemObject>?
) : RecyclerView.Adapter<RecyclerViewHolders>() {
    
    @NonNull
    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerViewHolders {
        val layoutView = LayoutInflater.from(parent.context).inflate(R.layout.list_layout, null)
        return RecyclerViewHolders(layoutView)
    }
    
    override fun onBindViewHolder(holder: RecyclerViewHolders, position: Int) {
        holder.awardTitle.text = "Award Title: " + itemList!![position].awardTitle
        holder.awardYear.text = "Award Year: " + itemList[position].awardYear
        holder.player.text = "Player Name: " + itemList[position].player
    }
    
    override fun getItemCount(): Int {
        return this.itemList!!.size
    }
}

RecyclerViewHolders.kt

import android.util.SparseBooleanArray
import android.view.View
import android.widget.TextView
import androidx.recyclerview.widget.RecyclerView.ViewHolder

class RecyclerViewHolders(itemView: View) : ViewHolder(itemView), View.OnClickListener {
    var awardTitle: TextView
    var awardYear: TextView
    var player: TextView
    private val selectedItems = SparseBooleanArray()
    
    override fun onClick(view: View) {
        if (selectedItems[adapterPosition, false]) {
            selectedItems.delete(adapterPosition)
            view.isSelected = false
        } else {
            selectedItems.put(adapterPosition, true)
            view.isSelected = true
        }
    }
    
    init {
        itemView.setOnClickListener(this)
        awardTitle = itemView.findViewById(R.id.awardTitle)
        awardYear = itemView.findViewById(R.id.awardYear)
        player = itemView.findViewById(R.id.playerName)
    }
}

SimpleItemDecoration.kt

import android.content.Context
import android.graphics.Canvas
import android.graphics.drawable.Drawable
import androidx.annotation.NonNull
import androidx.core.content.ContextCompat
import androidx.recyclerview.widget.RecyclerView

internal class SimpleItemDecoration(context: Context) : RecyclerView.ItemDecoration() {
    private val drawable: Drawable = ContextCompat.getDrawable(context, R.drawable.line_divider)!!
    
    override fun onDrawOver(
        @NonNull canvas: Canvas,
        parent: RecyclerView,
        @NonNull state: RecyclerView.State
    ) {
        val left = parent.paddingLeft
        val right = parent.width - parent.paddingRight
        val childCount = parent.childCount
        
        for (i in 0 until childCount) {
            val child = parent.getChildAt(i)
            val params = child.layoutParams as RecyclerView.LayoutParams
            val top = child.bottom + params.bottomMargin
            val bottom = top + drawable.intrinsicHeight
            drawable.setBounds(left, top, right, bottom)
            drawable.draw(canvas)
        }
    }
}

Bước 5: Tạo các file drawable

background_selector.xml

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="https://schemas.android.com/apk/res/android">
    <item android:drawable="@android:color/holo_green_light" 
          android:state_pressed="false" android:state_selected="true" />
    <item android:drawable="@android:color/holo_purple" android:state_selected="false" />
</selector>

line_divider.xml

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="https://schemas.android.com/apk/res/android"
    android:shape="rectangle">
    <size android:width="2dp" android:height="2dp" />
    <solid android:color="@color/colorPrimaryDark" />
</shape>

Bước 6: Tạo layout item (list_layout.xml)

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="https://schemas.android.com/apk/res/android"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@drawable/background_selector"
    android:padding="16dp">
    <TextView
        android:id="@+id/awardTitle"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="10dp"
        android:text="New Text"
        android:textColor="@android:color/background_dark"
        android:textSize="18sp"
        android:textStyle="bold" />
    <TextView
        android:id="@+id/awardYear"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/awardTitle"
        android:layout_alignStart="@id/awardTitle"
        android:layout_marginTop="20dp"
        android:text="New Text"
        android:textColor="@android:color/background_dark" />
    <TextView
        android:id="@+id/playerName"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentEnd="true"
        android:layout_marginBottom="10dp"
        android:text="New Text"
        android:textColor="@android:color/background_dark" />
</RelativeLayout>

Bước 7: Cấu hình AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="https://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>

Chạy ứng dụng

Kết nối thiết bị Android thực với máy tính. Từ Android Studio, mở file activity và nhấn biểu tượng Run trên thanh công cụ. Chọn thiết bị di động và kiểm tra màn hình hiển thị.