kotlin.UninitializedPropertyAccessException - lateinit 属性 mAdapter 尚未初始化 - Android 开发

Question

我正在 android 中制作一个新闻应用程序，但是当我从我的应用程序调用 API(http) 时出现错误。我不知道为什么会出现错误我实现了所有 class、memebers、函数。请帮助我。

错误描述如下

2021-01-21 09:21:25.896 18052-18052/com.arne.khabriapp E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.arne.khabriapp, PID: 18052
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.arne.khabriapp/com.arne.khabriapp.MainActivity}: kotlin.UninitializedPropertyAccessException: lateinit property mAdapter has not been initialized
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3270)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409)
    at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
    at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016)
    at android.os.Handler.dispatchMessage(Handler.java:107)
    at android.os.Looper.loop(Looper.java:214)
    at android.app.ActivityThread.main(ActivityThread.java:7356)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
 Caused by: kotlin.UninitializedPropertyAccessException: lateinit property mAdapter has not been initialized
    at com.arne.khabriapp.MainActivity.onCreate(MainActivity.kt:25)
    at android.app.Activity.performCreate(Activity.java:7802)
    at android.app.Activity.performCreate(Activity.java:7791)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1299)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3245)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409) 
    at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83) 
    at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016) 
    at android.os.Handler.dispatchMessage(Handler.java:107) 
    at android.os.Looper.loop(Looper.java:214) 
    at android.app.ActivityThread.main(ActivityThread.java:7356) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930) 
2021-01-21 09:21:25.912 18052-18090/com.arne.khabriapp D/NetworkSecurityConfig: 
No Network Security Config specified, using platform default

这是我的MainActivity.kt

    package com.arne.khabriapp

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.Toast
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.RecyclerView
import com.android.volley.Request
import com.android.volley.toolbox.JsonObjectRequest


class MainActivity : AppCompatActivity(), NewsItemClicked {

    private lateinit var  mAdapter: NewsListAdapter
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val recyclerView = findViewById<RecyclerView>(R.id.rView)
        recyclerView.layoutManager  = LinearLayoutManager(this)
//        recyclerView.layoutManager  = GridLayoutManager(this,12)
//        recyclerView.layoutManager   = StaggeredGridLayoutManager(15,12)
         fetchData()

        recyclerView.adapter = mAdapter


    }

    private fun fetchData() {
//        val list = ArrayList<String>()
//        for(i in 0 until 100){
//            list.add("item $i")
//        }
//        return list
        val url = "https://newsapi.org/v2/top-headlines?country=in&apiKey=9bb7bf6152d147ad8ba14cd0e7452f2f"
        val jsonObjectRequest = JsonObjectRequest(
            Request.Method.GET,
            url,
            null,
            {
                val newsJsonArray = it.getJSONArray("articles")
                val newsArray = ArrayList<NewsClass>()
                for (i in 0 until newsJsonArray.length()){
                    val newsJsonObject = newsJsonArray.getJSONObject(i)
                    val news =NewsClass(
                        newsJsonObject.getString("title"),
                        newsJsonObject.getString("author"),
                        newsJsonObject.getString("url"),
                        newsJsonObject.getString("urlToImage")
                    )
                    newsArray.add(news)
                }
                mAdapter.updateNews(newsArray)
            },
            {

            }

        )
        MySingletonClass.getInstance(this).addRequestQueue(jsonObjectRequest)

    }

    override fun OnItemClick(item: NewsClass) {

    }
}

这是我的NewsAdapter.kt

package com.arne.khabriapp

import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.TextView
import androidx.recyclerview.widget.RecyclerView

//class Name: extendItForRecyclerView.Adapter<ViewHolderClass>
class NewsListAdapter( private val listener: NewsItemClicked): RecyclerView.Adapter<NewsViewHolder>()
{

    private val items: ArrayList<NewsClass> = ArrayList()
//    call me when each time one viewholder is created
    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): NewsViewHolder {

    //Layout Inflater  - Converts XML into View
    val view = LayoutInflater.from(parent.context).inflate(R.layout.itemnews, parent, false)

    val viewHolder = NewsViewHolder(view)
    view.setOnClickListener{
        //this is a call back to main activity so the main activity knows that any item is clicked and then the mainn activity behave according to this.
        listener.OnItemClick(items[viewHolder.adapterPosition])
        
    }
        return viewHolder
    }

    //    I will bind the item with viewholder
    override fun onBindViewHolder(holder: NewsViewHolder, position: Int) {
        val currentItem = items[position]
        holder.titleView.text = currentItem.title
    }


//    call me only one time i will give you how many item will be here in list
    override fun getItemCount(): Int {
        return items.size
    }

    fun updateNews(updatedNews: ArrayList<NewsClass>){
        items.clear()
        items.addAll(updatedNews)

        notifyDataSetChanged()
    }
}
class NewsViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView){
    val titleView: TextView = itemView.findViewById(R.id.title)
}

interface NewsItemClicked{
    fun OnItemClick(item: NewsClass)
}

请回答 非常感谢您的进阶

Answer 1

你可以这样做。

 private lateinit var  mAdapter: NewsListAdapter
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val recyclerView = findViewById<RecyclerView>(R.id.rView)
        recyclerView.layoutManager  = LinearLayoutManager(this)
//        recyclerView.layoutManager  = GridLayoutManager(this,12)
//        recyclerView.layoutManager   = StaggeredGridLayoutManager(15,12)
         mAdapter  = NewsListAdapter(this)//should be inited before use.
         fetchData()
        recyclerView.adapter = mAdapter
    }

或者你也可以这样做

private val mAdapter: NewsListAdapter by lazy{
   NewsListAdapter(this)
}

kotlin.UninitializedPropertyAccessException - lateinit 属性 mAdapter 尚未初始化 - Android 开发

kotlin.UninitializedPropertyAccessException - lateinit property mAdapter has not been initialized - Android Development

android

android-studio

kotlin

android-recyclerview

android-volley