带有recyclerView(上下文)的片段中出错

Question

我将Kotlin与SDK版本29一起使用。我搜索了几个网站，但没有找到任何关于这个主题的内容。我想使用适配器在我的片段中使用recyclerview，但有一个关于适配器的错误我无法解决。

错误如下：

类型不匹配：推断的类型为Flux，但应为Context

它来自片段中的下一行：

adapter=PostsAdapter(this，posts(

你知道如何设置上下文吗？

这是我的代码：

适配器：

导入：

import android.content.Context 
import android.text.format.DateUtils
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.recyclerview.widget.RecyclerView
import com.bumptech.glide.Glide
import com.example.givenaskv1.R
import kotlinx.android.synthetic.main.item_post.view.*

代码：

class PostsAdapter (val context: Context, val posts : List<Post>) :
RecyclerView.Adapter<PostsAdapter.ViewHolder>() {
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
val view = LayoutInflater.from(context).inflate(R.layout.item_post, 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) {
itemView.tvUsername.text = post.user?.firstName
itemView.tvDescription.text = post.description
Glide.with(context).load(post.imageUrl).into(itemView.ivPost)
itemView.tvRelativeTime.text = DateUtils.getRelativeTimeSpanString(post.creationTimeMs)
}
}
}

片段：

导入：

import android.os.Bundle
import android.util.Log
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.fragment.app.Fragment
import androidx.recyclerview.widget.LinearLayoutManager
import com.example.givenaskv1.R
import com.example.givenaskv1.models.Post
import com.example.givenaskv1.models.PostsAdapter
import com.google.firebase.firestore.FirebaseFirestore
import com.google.firebase.firestore.Query
import kotlinx.android.synthetic.main.fragment_flux.*

代码：

private const val TAG = "Flux"
class Flux : Fragment() {
private lateinit var firestoreDb : FirebaseFirestore
private lateinit var posts : MutableList<Post>
private lateinit var adapter: PostsAdapter
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)

posts = mutableListOf()
adapter = PostsAdapter(this, posts)  <----- HERE IS THE ERROR
rvPosts.adapter = adapter
rvPosts.layoutManager = LinearLayoutManager(this.context)

firestoreDb = FirebaseFirestore.getInstance()
val postsReference = firestoreDb.collection("post")
// .limit() indique le nombre de post MAXIMIM a afficher en même temps, pour éviter le lagg
.limit(20)
// .orderBy() filtre selon le critère choisi (ici par ordre chonologique)
.orderBy("creation_time_ms", Query.Direction.DESCENDING)
postsReference.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 onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.fragment_flux, container, false)
}
}

fragment.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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="match_parent"
android:orientation="vertical"
tools:context=".Flux.Flux">
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/rvPosts"
android:layout_width="match_parent"
android:layout_height="match_parent" />
</LinearLayout>

当我试图更换时

adapter = PostsAdapter(this, posts)

带有

adapter = PostsAdapter(requireContext(), posts)

存在以下错误：

java.lang.IollegalStateException：rvPosts不能为null

非常感谢！

Answer 1

这是因为在创建片段视图之前，您在片段onCreate回调中获得了RecyclerView实例；由于onCreate()回调在onCreateView()回调之前触发

注意：片段视图是由onCreateView()创建并返回的。

为了解决这个问题，将代码从onCreate()转移到onCreateView()

private const val TAG = "Flux"
class Flux : Fragment() {
private lateinit var firestoreDb : FirebaseFirestore
private lateinit var posts : MutableList<Post>
private lateinit var adapter: PostsAdapter
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
}
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
// Inflate the layout for this fragment
val view = inflater.inflate(R.layout.fragment_flux, container, false)
posts = mutableListOf()
adapter = PostsAdapter(requireContext(), posts) 

val rvPosts = view.findViewById<RecyclerView>(R.id.rvPosts)
rvPosts.adapter = adapter
rvPosts.layoutManager = LinearLayoutManager(this.context)

firestoreDb = FirebaseFirestore.getInstance()
val postsReference = firestoreDb.collection("post")
// .limit() indique le nombre de post MAXIMIM a afficher en même temps, pour éviter le lagg
.limit(20)
// .orderBy() filtre selon le critère choisi (ici par ordre chonologique)
.orderBy("creation_time_ms", Query.Direction.DESCENDING)
postsReference.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}")
}
return view
}
}