如何使用 Kotlin 创建多级 ListView？

此示例演示了如何使用 Kotlin Android 创建多级 ListView。

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

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

<?xml version="1.0" encoding="utf-8"?>
<ExpandableListView xmlns:android="http://schemas.android.com/apk/res/android"
   xmlns:app="http://schemas.android.com/apk/res-auto"
   xmlns:tools="http://schemas.android.com/tools"
   android:id="@+id/expandableListView"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   tools:context=".MainActivity">
</ExpandableListView>

步骤 3 - 将以下代码添加到 src/MainActivity.kt

package app.com.kotlinapp
import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
import kotlinx.android.synthetic.main.activity_main.*
class MainActivity : AppCompatActivity() {
   private val header: MutableList<String> = ArrayList()
   private val body: MutableList<MutableList<String>> = ArrayList()
   override fun onCreate(savedInstanceState: Bundle?) {
      super.onCreate(savedInstanceState)
      setContentView(R.layout.activity_main)
      val myFavCricketPlayers: MutableList<String> = ArrayList()
      myFavCricketPlayers.add("MS.Dhoni");
      myFavCricketPlayers.add("Sehwag");
      myFavCricketPlayers.add("Shane Watson");
      myFavCricketPlayers.add("Ricky Ponting");
      myFavCricketPlayers.add("Shahid Afridi");
      val myFavFootballPlayers: MutableList<String> = ArrayList()
      myFavFootballPlayers.add("Cristiano Ronaldo")
      myFavFootballPlayers.add("Lionel Messi")
      myFavFootballPlayers.add("Gareth Bale")
      myFavFootballPlayers.add("Neymar JR")
      myFavFootballPlayers.add("David de Gea")
      val myFavTennisPlayers: MutableList<String> = ArrayList()
      myFavTennisPlayers.add("Roger Federer")
      myFavTennisPlayers.add("Rafael Nadal")
      myFavTennisPlayers.add("Andy Murray")
      myFavTennisPlayers.add("Novak Jokovic")
      myFavTennisPlayers.add("Sania Mirza")
      header.add("myFavCricketPlayers")
      header.add("myFavFootballPlayers")
      header.add("myFavTennisPlayers")
      body.add(myFavCricketPlayers)
      body.add(myFavFootballPlayers)
      body.add(myFavTennisPlayers)
      expandableListView.setAdapter(CustomListAdapter(this, expandableListView, header, body))
   }
}

步骤 4 - 创建一个新的 Kotlin 类，并将以下代码添加到 src/CustomListAdapter.kt

package app.com.kotlinapp
import android.content.Context
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.BaseExpandableListAdapter
import android.widget.ExpandableListView
import android.widget.TextView
import android.widget.Toast
class CustomListAdapter(
   var context: Context,
   var expandableListView: ExpandableListView,
   var header: MutableList<String>,
   var body: MutableList<MutableList<String>>
) :
   BaseExpandableListAdapter() {
      override fun getGroup(groupPosition: Int): String {
         return header[groupPosition]
      }
   override fun isChildSelectable(groupPosition: Int, childPosition: Int): Boolean {
      return true
   }
   override fun hasStableIds(): Boolean {
      return false
   }
   override fun getGroupView(
      groupPosition: Int,
      isExpanded: Boolean,
      convertView: View?,
      parent: ViewGroup?
   ): View? {
   var convertView = convertView
   if (convertView == null) {
      val inflater = context.getSystemService(Context.LAYOUT_INFLATER_SERVICE) as LayoutInflater
convertView = inflater.inflate(R.layout.list_header, null)
   }
   val title = convertView?.findViewById<TextView>(R.id.textView)
   title?.text = getGroup(groupPosition)
   title?.setOnClickListener {
      if (expandableListView.isGroupExpanded(groupPosition))
         expandableListView.collapseGroup(groupPosition)
      else
         expandableListView.expandGroup(groupPosition)
         Toast.makeText(context, getGroup(groupPosition), Toast.LENGTH_SHORT).show()
      }
      return convertView
   }
   override fun getChildrenCount(groupPosition: Int): Int {
      return body[groupPosition].size
   }
   override fun getChild(groupPosition: Int, childPosition: Int): String {
      return body[groupPosition][childPosition]
   }
   override fun getGroupId(groupPosition: Int): Long {
      return groupPosition.toLong()
   }
   override fun getChildView(
      groupPosition: Int,
      childPosition: Int,
      isLastChild: Boolean,
      convertView: View?,
      parent: ViewGroup?
   ): View? {
   var convertView = convertView
   if (convertView == null) {
      val inflater =   context.getSystemService(Context.LAYOUT_INFLATER_SERVICE) as LayoutInflater
convertView = inflater.inflate(R.layout.list_body, null)
   }
   val title = convertView?.findViewById<TextView>(R.id.textView)
   title?.text = getChild(groupPosition, childPosition)
   return convertView
}
   override fun getChildId(groupPosition: Int, childPosition: Int): Long {
      return childPosition.toLong()
   }
   override fun getGroupCount(): Int {
      return header.size
   }
}

步骤 5 - 创建一个布局资源文件 (list_header.xml) 并添加以下代码 -

<?xml version="1.0" encoding="utf-8"?>
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
   android:id="@+id/textView"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   android:paddingStart="?android:attr/expandableListPreferredItemPaddingLeft"
   android:paddingTop="8dp"
   android:paddingEnd="8dp"
   android:paddingBottom="8dp"
   android:textStyle="bold">
</TextView>

步骤 6 - 创建一个布局资源文件 (list_body.xml) 并添加以下代码 -

<?xml version="1.0" encoding="utf-8"?>
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
   android:id="@+id/textView"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   android:paddingStart="?android:attr/expandableListPreferredItemPaddingLeft"
   android:paddingTop="8dp"
   android:paddingEnd="8dp"
   android:paddingBottom="8dp">
</TextView>

步骤 7 - 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.kotlinapp">
   <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&g;
</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，请打开项目的一个活动文件，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 -