如何使用Kotlin在Android中创建可扩展RecyclerView项目？

RecyclerView是作为GridView和ListView的后继者添加到android studio的ViewGroup。这是对两者的改进，可以在最新的v-7支持包中找到。创建它的目的是使具有XML布局的任何列表的构造成为可能，并且可以在极大地自定义项目的同时提高ListViews和GridViews的效率。通过回收用户看不见的视图来实现此改进。例如，如果用户向下滚动到可以看到项目4和5的位置，则向下滚动；第1、2和3项将从内存中清除，以减少内存消耗。在本文中，我们将说明如何在android中创建Expandable Recycler View项目。以下是示例视频，展示了我们将要构建的内容。请注意，我们将使用Kotlin语言实施此项目。

分步实施

步骤1：创建一个新项目

要在Android Studio中创建新项目，请参阅如何在Android Studio中创建/启动新项目。请注意，选择Kotlin作为编程语言。

步骤2：添加视图绑定依赖项

转到android标签内的build.gradle(app)和以下依赖项，然后单击立即同步。

 buildFeatures {

      viewBinding true

  }

步骤3：使用activity_main.xml

转到activity_main.xml文件，并参考以下代码。以下是activity_main.xml文件的代码。它只有一个Recycler视图，我们将用它来显示数据。

步骤4：创建一个新的布局文件并将其命名为single_item.xml文件

转到single_item.xml文件，并参考以下代码。以下是single_item.xml文件的代码。这是我们将在RecyclerView中使用的单个项目布局。

步骤5：创建一个新的模型类

创建一个新的Language.kt类，我们将使用自定义通用“ Language ”的数据来传递将在RecyclerView中显示的列表。

科特林

// 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

创建一个新的类RvAdapter.kt，它将充当回收者视图的Adapter类。可扩展回收站视图的逻辑是，首先，我们将ID为“ single_item.xm l”的“ expanded_view ”的布局的可见性更改为GONE ，一旦用户单击任何回收站视图的项目，我们将使其可见性为可见。为了更好的理解，在代码之前添加了注释。

科特林

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
) : RecyclerView.Adapter() {
  
    // 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
    }
}

步骤7：使用MainActivity.kt

转到MainActivity.kt文件，并参考以下代码。下面是MainActivity.kt文件的代码。在代码内部添加了注释，以更详细地了解代码。

科特林

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()
    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在这里。

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