问题描述
我将 Kotlin 与 SDK 版本 29 一起使用。 我在几个网站上搜索过,但没有找到关于这个主题的任何内容。 我想使用适配器在我的片段中使用 recyclerview,但有一个关于我的适配器的错误,我无法解决。
这里是错误:
类型不匹配:推断的类型是 Flux 但需要上下文
它来自片段的下一行:
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>
当我尝试替换时
adapter = PostsAdapter(this,posts)
与
adapter = PostsAdapter(requireContext(),posts)
出现以下错误:
java.lang.IllegalStateException: rvPosts 不能为 null
非常感谢!
解决方法
这是因为在创建片段视图之前,您在片段 RecyclerView
回调中获得了 onCreate
实例;由于onCreate()
回调在onCreateView()
回调
注意:片段视图由 onCreateView()
创建并返回。
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
}
}