尝试在空对象引用上调用虚拟方法“void android.view.View.setVisibility(int)”

Question

我正在尝试在片段中实现进度条，但它给了我这个错误。 我正在调用一个 api，它为我提供数据，在获取数据之前，我想运行进度条。

java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法“void android.view.View.setVisibility(int)”

这是代码

class GeneralFragment : Fragment() {

private lateinit var mAdapter: NewsListAdapter

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)

    fetchdata("https://news-api-don.herokuapp.com/api/v1?apiKey=20d14506791144cc8b424549c42068c0")

}


override fun onCreateView(
    inflater: LayoutInflater,
    container: ViewGroup?,
    savedInstanceState: Bundle?
): View? {
    return inflater.inflate(R.layout.fragment_general, container, false)

}

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
    super.onViewCreated(view, savedInstanceState)
    val recyclerView = view.findViewById<RecyclerView>(R.id.recyclerView)
    mAdapter = NewsListAdapter(this)
    recyclerView.adapter = mAdapter

}


private fun fetchdata(url: String) {
    generalBar.visibility = View.VISIBLE

    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)
            generalBar.visibility = View.GONE

        },
        {
            Toast.makeText(activity, "Something went wrong", Toast.LENGTH_LONG).show()
            generalBar.visibility = View.GONE

        }
    )


    MySingleton.getInstance(this).addToRequestQueue(jsonObjectRequest)

}

fun onItemClicked(item: News) {
    val builder = CustomTabsIntent.Builder()
    val customTabsIntent = builder.build()
    activity?.let { customTabsIntent.launchUrl(it, Uri.parse(item.url)) }
}

}

这是xml文件

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
xmlns:app="http://schemas.android.com/apk/res-auto"
tools:context=".fragments.GeneralFragment">

<androidx.recyclerview.widget.RecyclerView
    android:id="@+id/recyclerView"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"/>

<ProgressBar
    android:id="@+id/generalBar"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintTop_toTopOf="parent"/>


 </androidx.constraintlayout.widget.ConstraintLayout>

Answer 1

似乎generalBar在fetchdatacall 之前没有初始化。你需要初始化它

val generalBar = view.findViewById<ProgressBar>(R.id.generalBar)