"kotlin.UninitializedPropertyAccessException: lateinit property madapter has not been initialized at..." 在设置 RecyclerView Adapter 时

Question

换行错误：

recyclerView.adapter = mAdapter

代码：

class MainActivity : AppCompatActivity(), NewsItemClicked {
    private lateinit var recyclerView:RecyclerView
    private lateinit var mAdapter: NewsListAdapter

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        recyclerView = findViewById(R.id.recyclerView)
        fetchData()

        val verticalLayoutManager = LinearLayoutManager(this)
             recyclerView.layoutManager = verticalLayoutManager
        recyclerView.adapter = mAdapter
    }

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

            }

        )
        MySingleton.getInstance(this).addToRequestQueue(jsonObjectRequest)
    }
    override fun onItemClicked(item: News) {
        val builder = CustomTabsIntent.Builder()
        val customTabsIntent = builder.build()
        customTabsIntent.launchUrl(this, Uri.parse(item.url))
    }
}

来自 logcat 的错误：

2021-01-19 18:38:40.819 3869-3869/com.example.newsfresh E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.newsfresh, PID: 3869
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.newsfresh/com.example.newsfresh.MainActivity}: kotlin.UninitializedPropertyAccessException: lateinit property madapter has not been initialized
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2817)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2895)
        at android.app.ActivityThread.-wrap11(Unknown Source:0)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1616)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:176)
        at android.app.ActivityThread.main(ActivityThread.java:6651)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:547)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:824)
     Caused by: kotlin.UninitializedPropertyAccessException: lateinit property madapter has not been initialized
        at com.example.newsfresh.MainActivity.onCreate(MainActivity.kt:25)
        at android.app.Activity.performCreate(Activity.java:7088)
        at android.app.Activity.performCreate(Activity.java:7079)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1215)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2770)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2895) 
        at android.app.ActivityThread.-wrap11(Unknown Source:0) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1616) 
        at android.os.Handler.dispatchMessage(Handler.java:106) 
        at android.os.Looper.loop(Looper.java:176) 
        at android.app.ActivityThread.main(ActivityThread.java:6651) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:547) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:824) 

Answer 1

您还没有初始化您的 lateinit var mAdapter 变量。

Kotlin 允许您访问它，尽管它未初始化，因为它是 lateinit，但它会抛出此异常。您可以通过以下两种方式解决此问题：

删除 lateinit，在声明站点初始化：

在这种情况下，它可能是 val:

private val mAdapter = NewsListAdapter(...)

这假定您已准备好在 Activity 启动时设置适配器所需的一切。一旦数据可用，您可能需要对其调用 notify... 方法之一。

如果你不...

确保在使用前已初始化

mAdapter = NewsListAdapter(...)
recyclerView.adapter = mAdapter