如何在RecyclerView Adapter中替代已废弃的Kotlin Synthetics

数据老陈

2026-7-23

问题描述

我正在跟着一个教程搭建Instagram克隆应用，但教程里用了现已废弃的Kotlin Synthetics。我尝试改用findViewById，但似乎和当前使用的ViewHolder/RecyclerView不兼容，请问这种场景下该怎么替换Kotlin Synthetics？

PostAdapter.kt

package com.example.dndgroupfinder

import android.content.Context
import android.os.Bundle
import android.text.format.DateUtils
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.TextView
import androidx.recyclerview.widget.RecyclerView
import com.bumptech.glide.Glide
import com.example.dndgroupfinder.models.Post

private const val TAG = "post_item"

class PostAdapter (val context: Context, val posts: List<Post>) :
    RecyclerView.Adapter<PostAdapter.ViewHolder>() {


    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
        val view = LayoutInflater.from(context).inflate(R.layout.post_item, parent, false)
        return ViewHolder(view)

    }
    
    override fun getItemCount() = posts.size

    override fun onBindViewHolder(holder: ViewHolder, position: Int) {
        holder.bind(posts[position])

    }

    inner class  ViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
        fun bind(post: Post) {
            textViewUsername = view.findViewByID(R.id.textViewUsername)
            itemView.textViewUsername.text =post.user?.username
            itemView.textViewDescription.text = post.description
            Glide.with(context).load(post.imageUrl).into(itemView.imageViewPostImage)
            itemView.textViewPostTime.text = DateUtils.getRelativeTimeSpanString(post.creationTimeMs)
        }
    }
}

post_item.xml

<?xml version="1.0" encoding="utf-8"?>

<androidx.cardview.widget.CardView 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:layout_height="wrap_content"
    android:layout_margin="8dp">

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_marginTop="8dp"
    android:orientation="vertical">

    <TextView
        android:id="@+id/textViewUsername"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="TextView"
        android:textAppearance="@style/TextAppearance.AppCompat.Large"
        tools:text="Aidan" />

    <TextView
        android:id="@+id/textViewPostTime"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textSize="12sp"
        tools:text="5 days ago" />

    <ImageView
        android:id="@+id/imageViewPostImage"
        android:layout_width="match_parent"
        android:layout_height="300dp"
        android:scaleType="centerCrop"
        tools:src="@tools:sample/avatars"/>

    <TextView
        android:id="@+id/textViewDescription"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="4dp"
        android:text="@string/textview"
        tools:text="Here we go!!!" />
    
</LinearLayout>
</androidx.cardview.widget.CardView>

PostFeedActivity.kt

package com.example.dndgroupfinder

import android.content.Intent
import android.os.Bundle
import android.util.Log
import android.view.Menu
import android.view.MenuItem
import android.widget.Button
import androidx.activity.ComponentActivity
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.RecyclerView
import com.example.dndgroupfinder.models.Post
import com.google.firebase.firestore.FirebaseFirestore
import com.google.firebase.firestore.Query

private const val TAG = "PostFeedActivity"
class PostFeedActivity : ComponentActivity() {

    private lateinit var firestoreDatabase: FirebaseFirestore
    private lateinit var posts: MutableList<Post>
    private lateinit var adapter: PostAdapter

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.postfeed_activity)

        //Layout file for one post -Done
        //create data source -Done
        posts = mutableListOf()
        //create adapter
        adapter = PostAdapter(this, posts)
        //bind adapter and layout manager to RV

        val recviewposts = findViewById<RecyclerView>(R.id.recviewposts)
        recviewposts.adapter = adapter
        recviewposts.layoutManager = LinearLayoutManager(this)


        firestoreDatabase = FirebaseFirestore.getInstance()
        val postFeedReference = firestoreDatabase
            .collection("posts")
            .limit(20)
            .orderBy("creation_time_ms", Query.Direction.DESCENDING)

        postFeedReference.addSnapshotListener{snapshot, exception ->
            if (exception != null || snapshot == null) {
                Log.e(TAG, "Exception when querying posts", exception)
                return@addSnapshotListener
            }
            val postList = snapshot.toObjects(Post::class.java)
            posts.clear()
            posts.addAll(postList)
            adapter.notifyDataSetChanged()
            for (post in postList) {
                Log.i(TAG, "Post $post")
            }
        }


    }

    override fun onCreateOptionsMenu(menu: Menu?): Boolean {
        menuInflater.inflate(R.menu.postfeed_menu, menu)
        return super.onCreateOptionsMenu(menu)
    }

    override fun onOptionsItemSelected(item: MenuItem): Boolean {
        if (item.itemId == R.id.menuToProfile) {
            val intent = Intent(this, UserProfileActivity::class.java)
            startActivity(intent)
        }
        return super.onOptionsItemSelected(item)
    }
}

解决方案

方案1：直接在ViewHolder中初始化`findViewById`

这是无需额外依赖的基础方案，核心是在ViewHolder构造时一次性查找所有需要的View，避免每次绑定数据时重复查找，同时修正你原代码中的错误（原代码误用了view对象，ViewHolder中只有itemView）。

修改后的PostAdapter.kt代码：

package com.example.dndgroupfinder

import android.content.Context
import android.text.format.DateUtils
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.ImageView
import android.widget.TextView
import androidx.recyclerview.widget.RecyclerView
import com.bumptech.glide.Glide
import com.example.dndgroupfinder.models.Post

private const val TAG = "post_item"

class PostAdapter(val context: Context, val posts: List<Post>) :
    RecyclerView.Adapter<PostAdapter.ViewHolder>() {

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
        val view = LayoutInflater.from(context).inflate(R.layout.post_item, parent, false)
        return ViewHolder(view)
    }

    override fun getItemCount() = posts.size

    override fun onBindViewHolder(holder: ViewHolder, position: Int) {
        holder.bind(posts[position])
    }

    inner class ViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
        // 构造时一次性初始化所有需要的View
        private val tvUsername: TextView = itemView.findViewById(R.id.textViewUsername)
        private val tvPostTime: TextView = itemView.findViewById(R.id.textViewPostTime)
        private val ivPostImage: ImageView = itemView.findViewById(R.id.imageViewPostImage)
        private val tvDescription: TextView = itemView.findViewById(R.id.textViewDescription)

        fun bind(post: Post) {
            tvUsername.text = post.user?.username
            tvDescription.text = post.description
            Glide.with(context).load(post.imageUrl).into(ivPostImage)
            tvPostTime.text = DateUtils.getRelativeTimeSpanString(post.creationTimeMs)
        }
    }
}

方案2：使用View Binding（官方推荐）

这是Google官方推荐的替代Kotlin Synthetics的方案，类型安全且无需手动编写findViewById代码。

步骤1：开启View Binding

在模块级build.gradle.kts或build.gradle中添加配置：

// build.gradle.kts 版本
android {
    buildFeatures {
        viewBinding = true
    }
}

// build.gradle 版本
android {
    buildFeatures {
        viewBinding true
    }
}

步骤2：修改`PostAdapter.kt`

package com.example.dndgroupfinder

import android.content.Context
import android.text.format.DateUtils
import android.view.LayoutInflater
import android.view.ViewGroup
import androidx.recyclerview.widget.RecyclerView
import com.bumptech.glide.Glide
import com.example.dndgroupfinder.databinding.PostItemBinding
import com.example.dndgroupfinder.models.Post

private const val TAG = "post_item"

class PostAdapter(val context: Context, val posts: List<Post>) :
    RecyclerView.Adapter<PostAdapter.ViewHolder>() {

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
        // 使用View Binding加载布局
        val binding = PostItemBinding.inflate(LayoutInflater.from(context), parent, false)
        return ViewHolder(binding)
    }

    override fun getItemCount() = posts.size

    override fun onBindViewHolder(holder: ViewHolder, position: Int) {
        holder.bind(posts[position])
    }

    // ViewHolder持有Binding对象
    inner class ViewHolder(private val binding: PostItemBinding) : RecyclerView.ViewHolder(binding.root) {
        fun bind(post: Post) {
            binding.textViewUsername.text = post.user?.username
            binding.textViewDescription.text = post.description
            Glide.with(context).load(post.imageUrl).into(binding.imageViewPostImage)
            binding.textViewPostTime.text = DateUtils.getRelativeTimeSpanString(post.creationTimeMs)
        }
    }
}

关键注意点

原代码中view.findViewByID是错误写法，ViewHolder中只能使用构造时传入的itemView对象
无论哪种方案，都要避免在bind方法中重复查找View，应该在ViewHolder构造阶段一次性完成，提升RecyclerView的滚动性能

内容的提问来源于stack exchange，提问作者Aidan Moore

如何在RecyclerView Adapter中替代已废弃的Kotlin Synthetics

PostAdapter.kt #

post_item.xml #

PostFeedActivity.kt #

方案1：直接在ViewHolder中初始化findViewById #

方案2：使用View Binding（官方推荐） #