如何使用 Kotlin 在安卓中创建可扩展的 RecyclerView 项目？
原文:https://www . geeksforgeeks . org/how-create-expandable-recycle view-items-in-Android-use-kot Lin/
【recycle view】是作为 GridView 和 ListView 的继承者加入安卓工作室的一个视图组。这是对两者的改进，可以在最新的 v-7 支持包中找到。它的创建是为了能够将任何带有 XML 布局的列表构建为一个项目，这样就可以进行大量定制，而 则提高了列表视图和网格视图 的效率。这种改进是通过回收用户不可见的视图来实现的。例如，如果用户向下滚动到项目 4 和 5 可见的位置；项目 1、2 和 3 将从内存中清除，以减少内存消耗。在本文中，我们将解释如何在 android 中创建可扩展的 Recycler View 项目。下面是展示我们将要构建的内容的示例视频。注意，我们将使用 Kotlin 语言来实现这个项目。
分步实施
第一步:创建新项目
要在安卓工作室创建新项目，请参考如何在安卓工作室创建/启动新项目。注意选择科特林作为编程语言。
第二步:添加视图绑定依赖关系
转到 build.gradle(app) 和安卓标签内的以下依赖项，点击立即同步。
构建功能{
视图绑定为真
}
步骤 3:使用 activity_main.xml
转到 activity_main.xml 文件，参考以下代码。下面是 activity_main.xml 文件的代码。它只有一个回收视图，我们将使用它来显示我们的数据。
可扩展标记语言
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
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:layout_width="match_parent"
android:background="#F5F8FD"
android:layout_height="match_parent"
tools:context=".MainActivity">
<!--Add recycler view to main activity-->
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/rv_list"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:listitem="@layout/single_item"
app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager" />
</androidx.constraintlayout.widget.ConstraintLayout>
第四步:新建布局文件，命名为 single_item.xml 文件
转到 single_item.xml 文件，参考以下代码。下面是 single_item.xml 文件的代码。这是我们将在回收视图中使用的单一项目布局。
可扩展标记语言
<?xml version="1.0" encoding="utf-8"?>
<com.google.android.material.card.MaterialCardView
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:id="@+id/card_layout"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginStart="5dp"
android:layout_marginEnd="5dp"
android:layout_marginBottom="10dp">
<androidx.constraintlayout.widget.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="match_parent">
<!--Text view for showing the language name-->
<TextView
android:id="@+id/tv_lang_name"
android:layout_width="wrap_content"
android:layout_height="40dp"
android:layout_marginStart="20dp"
android:layout_marginTop="10dp"
android:text="Language"
android:textColor="@color/black"
android:textSize="20sp"
android:textStyle="bold"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<!--This is the layout "expanded_view" we will
hide initially and show as expanded
layout when user clicks on any of the item-->
<RelativeLayout
android:id="@+id/expanded_view"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="10dp"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toBottomOf="@id/tv_lang_name">
<!--It has a text view which we will use in our case as
a description text for the languages-->
<TextView
android:id="@+id/tv_description"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_margin="10dp"
android:text="Description Text"
android:textSize="18sp" />
</RelativeLayout>
</androidx.constraintlayout.widget.ConstraintLayout>
</com.google.android.material.card.MaterialCardView>
第五步:新建模型类
创建一个新的类 Language.kt 我们将使用自定义通用“语言的数据来传入将在 RecyclerView 中显示的列表。
我的锅
// this is the Language model class
class Language(
val name : String ="",
val description : String= "",
var expand : Boolean = false
)
步骤 6:使用适配器类
创建一个新类 RvAdapter.kt 这将作为回收视图的适配器类。可扩展回收器视图背后的逻辑是，最初，我们将使 id 为“的布局的可见性从“ single_item.xm l”扩展到 GONE ，一旦用户点击回收器视图的任何项目，我们将使其可见性可见。为了更好的理解，代码前增加了注释。
我的锅
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.recyclerview.widget.RecyclerView
import com.geeksforgeeks.rvadapterviewbinding.databinding.SingleItemBinding
class RvAdapter(
private var languageList: List<Language>
) : RecyclerView.Adapter<RvAdapter.ViewHolder>() {
// create an inner class with name ViewHolder
// It takes a view argument, in which pass the generated class of single_item.xml
// ie SingleItemBinding and in the RecyclerView.ViewHolder(binding.root) pass it like this
inner class ViewHolder(val binding: SingleItemBinding) : RecyclerView.ViewHolder(binding.root)
// inside the onCreateViewHolder inflate the view of SingleItemBinding
// and return new ViewHolder object containing this layout
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
val binding = SingleItemBinding.inflate(LayoutInflater.from(parent.context), parent, false)
return ViewHolder(binding)
}
// bind the items with each item of the list languageList which than will be
// shown in recycler view
// to keep it simple we are not setting any image data to view
override fun onBindViewHolder(holder: ViewHolder, position: Int) {
with(holder){
with(languageList[position]){
// set name of the language from the list
binding.tvLangName.text = this.name
// set description to the text
// since this is inside "expandedView" its visibility will be gone initially
// after click on the item we will make the visibility of the "expandedView" visible
// which will also make the visibility of desc also visible
binding.tvDescription.text = this.description
// check if boolean property "extend" is true or false
// if it is true make the "extendedView" Visible
binding.expandedView.visibility = if (this.expand) View.VISIBLE else View.GONE
// on Click of the item take parent card view in our case
// revert the boolean "expand"
binding.cardLayout.setOnClickListener {
this.expand = !this.expand
notifyDataSetChanged()
}
}
}
}
// return the size of languageList
override fun getItemCount(): Int {
return languageList.size
}
}
第 7 步:使用 MainActivity.kt
转到 MainActivity.kt 文件，参考以下代码。下面是 MainActivity.kt 文件的代码。代码中添加了注释，以更详细地理解代码。
我的锅
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import androidx.recyclerview.widget.LinearLayoutManager
import com.geeksforgeeks.rvadapterviewbinding.databinding.ActivityMainBinding
class MainActivity : AppCompatActivity() {
// view binding for the activity
private var _binding: ActivityMainBinding? = null
private val binding get() = _binding!!
// get reference to the adapter class
private var languageList = ArrayList<Language>()
private lateinit var rvAdapter: RvAdapter
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
_binding = ActivityMainBinding.inflate(layoutInflater)
setContentView(binding.root)
// define layout manager for the Recycler view
binding.rvList.layoutManager = LinearLayoutManager(this)
// attach adapter to the recycler view
rvAdapter = RvAdapter(languageList)
binding.rvList.adapter = rvAdapter
// create new objects
// add some row data
val language1 = Language(
"Java",
"Java is an Object Oriented Programming language." +
" Java is used in all kind of applications like Mobile Applications (Android is Java based), " +
"desktop applications, web applications, client server applications, enterprise applications and many more. ",
false
)
val language2 = Language(
"Kotlin",
"Kotlin is a statically typed, general-purpose programming language" +
" developed by JetBrains, that has built world-class IDEs like IntelliJ IDEA, PhpStorm, Appcode, etc.",
false
)
val language3 = Language(
"Python",
"Python is a high-level, general-purpose and a very popular programming language." +
" Python programming language (latest Python 3) is being used in web development, Machine Learning applications, " +
"along with all cutting edge technology in Software Industry.",
false
)
val language4 = Language(
"CPP",
"C++ is a general purpose programming language and widely used now a days for " +
"competitive programming. It has imperative, object-oriented and generic programming features. ",
false
)
// add items to list
languageList.add(language1)
languageList.add(language2)
languageList.add(language3)
languageList.add(language4)
rvAdapter.notifyDataSetChanged()
}
// on destroy of view make the binding reference to null
override fun onDestroy() {
super.onDestroy()
_binding = null
}
}
输出:
Github Repo 此处 。
