如何使用 Kotlin 获取 listView 中所有选中的项目？

此示例演示了如何使用 Kotlin 获取 listView 中所有选中的项目。

步骤 1 &minusl 在 Android Studio 中创建一个新项目，转到文件 ⇒ 新建项目，并填写所有必需的详细信息以创建新项目。

步骤 2 &minusl 将以下代码添加到 res/layout/activity_main.xml。

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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:orientation="vertical"
   android:padding="16dp"
   tools:context="MainActivity">
   <ListView
      android:id="@+id/listView"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      android:layout_weight="1">
   </ListView>
   <LinearLayout
      android:layout_width="match_parent"
      android:layout_height="50dp"
      android:orientation="horizontal">
   <Button
      android:id="@+id/select"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:layout_gravity="center"
      android:layout_weight="1"
      android:text="Select all" />
   <Button
      android:id="@+id/deSelect"
      android:layout_width="match_parent"
      android:layout_height="50dp"
      android:layout_weight="1"
      android:text="Deselect all" />
   <Button
      android:id="@+id/viewSelected"
      android:layout_width="match_parent"
      android:layout_height="50dp"
      android:layout_weight="1"
      android:text="Next activity"
      android:visibility="visible" />
   </LinearLayout>
</LinearLayout>

步骤 3 &minusl 创建一个 Java 类（CustomAdapter.kt）并添加以下代码

package app.com.myapplication
import android.content.Context
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.BaseAdapter
import android.widget.CheckBox
import android.widget.TextView
import android.widget.Toast
class CustomAdapter(private val context: Context, private var modelArrayList: ArrayList<Model>) :
BaseAdapter() {
   override fun getViewTypeCount(): Int {
      return count
   }
   override fun getItemViewType(position: Int): Int {
      return position
   }
   override fun getCount(): Int {
      return modelArrayList.size
   }
   override fun getItem(position: Int): Any {
      return modelArrayList[position]
   }
   override fun getItemId(position: Int): Long {
      return 0
   }
   override fun getView(position: Int, convertView: View?, parent: ViewGroup): View {
      var convertView: View? = convertView
      val holder: ViewHolder
      if (convertView == null) {
         holder = ViewHolder()
         val inflater = context.getSystemService(Context.LAYOUT_INFLATER_SERVICE) 
            as LayoutInflater convertView = inflater.inflate(R.layout.listitem, null, true)
         holder.checkBox = convertView!!.findViewById(R.id.checkBox) as CheckBox holder.tvPlayer = convertView.findViewById(R.id.playerNameList) as TextView
         convertView.tag = holder
      }
      else {
         // the getTag returns the viewHolder object set as a tag to the view
         holder = convertView.tag as ViewHolder
      }
      holder.checkBox?.text = "Checkbox $position"
      holder.tvPlayer!!.text = modelArrayList[position].getPlayer()
      holder.checkBox!!.isChecked = modelArrayList[position].getSelected()
      holder.checkBox!!.setTag(R.integer.btnPlusPos, convertView)
      holder.checkBox!!.tag = position
      holder.checkBox!!.setOnClickListener {
         val pos = holder.checkBox!!.tag as Int
         Toast.makeText(
            context, "Checkbox " + pos + "Clicked!",
            Toast.LENGTH_SHORT
         ).show()
         if (modelArrayList[pos].getSelected()) {
            modelArrayList[pos].setSelected(false)
         }
         else {
            modelArrayList[pos].setSelected(true)
         }
      }
   return convertView
}
private inner class ViewHolder {
   var checkBox: CheckBox? = null
   var tvPlayer: TextView? = null
}

步骤 4 &minusl 创建一个 Java 类（Model.kt）并添加以下代码

package app.com.myapplication
class Model {
   private var isSelected = false
   private var player: String? = null
   fun getPlayer(): String? {
      return player
   }
   fun setPlayer(player: String?) {
      this.player = player
   }
   fun getSelected(): Boolean {
      return isSelected
   }
   fun setSelected(selected: Boolean) {
      isSelected = selected
   }
}

步骤 5 &minusl 在 res/values/strings.xml 中添加以下代码

<integer name="btnPlusView">1</integer>
<integer name="btnPlusPos">2</integer>

步骤 6 &minusl 为你的 listView 创建一个布局 (listItem.xml) 并添加以下代码

<?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="horizontal">
   <CheckBox
      android:id="@+id/checkBox"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content" />
   <TextView
      android:id="@+id/playerNameList"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_marginStart="20dp"
      android:textSize="20sp" />
</LinearLayout>

步骤 7 &minusl 将以下代码添加到 src/MainActivity.kt

package app.com.myapplication
import android.os.Bundle
import android.widget.Button
import android.widget.ListView
import android.widget.Toast
import androidx.appcompat.app.AppCompatActivity
class MainActivity : AppCompatActivity() {
   private var listView: ListView? = null
   private var modelArrayList: ArrayList<Model>? = null
   private var customAdapter: CustomAdapter? = null
   lateinit var btnSelect: Button
   lateinit var btnDeSelect: Button
   val playerList = arrayOf(
      "Sunil Chetri - INDIA",
      "Cristiano Ronaldo - Portugal",
      "Lionel Messi - Argentina",
      "Neymar Jr - Brazil",
      "Eden Hazard - Belgium",
      "Gigi Buffon - Italy",
      "James Rodrigues - Columbia",
      "Sadio Mane - Senegal",
      "Toni Kroos - Germany"
   )
   override fun onCreate(savedInstanceState: Bundle?) {
      super.onCreate(savedInstanceState)
      setContentView(R.layout.activity_main)
      listView = findViewById(R.id.listView)
      btnSelect = findViewById(R.id.select)
      btnDeSelect = findViewById(R.id.deSelect)
      modelArrayList = getModel(false)
      customAdapter = CustomAdapter(this, modelArrayList!!)
      listView!!.adapter = customAdapter
      btnSelect.setOnClickListener {
         modelArrayList = getModel(true)
         customAdapter = CustomAdapter(this@MainActivity, modelArrayList!!)
         listView!!.adapter = customAdapter
         Toast.makeText(
            applicationContext, "Checked all items",
            Toast.LENGTH_SHORT
            ).show()
         }
         btnDeSelect.setOnClickListener {
            modelArrayList = getModel(false)
            customAdapter = CustomAdapter(this@MainActivity, modelArrayList!!)
            listView!!.adapter = customAdapter
            Toast.makeText(
               applicationContext, "Unchecked all items",
               Toast.LENGTH_SHORT
            ).show()
         }
      }
      private fun getModel(isSelect: Boolean): java.util.ArrayList<Model>? {
         val list: ArrayList<Model> = ArrayList()
         for (i in 0..8) {
            val model = Model()
            model.setSelected(isSelect)
            model.setPlayer(playerList[i])
            list.add(model)
         }
         return list
   }
}

步骤 8 &minusl 将以下代码添加到 androidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
   package="app.com.myapplication">
   <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电脑。要从 Android Studio 运行应用程序，请打开您的项目之一的活动文件，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