Question

此应用直接从API获取数据。当它运行时会发生这种类型的错误。基本上我认为错误发生在getItemCount（）方法中，但我无法解决问题。我已经附上了错误文件和整个代码。如果您能解决错误，我将非常感激。

java.lang.NullPointerException：尝试调用接口方法＆＃39; int java.util.List.size（）＆＃39;在null对象引用上在 com.techbrightsoft.database.MyRecyler.getItemCount（MyRecyler.java:36）在 android.support.v7.widget.RecyclerView.dispatchLayoutStep1（RecyclerView.java:3603）在 android.support.v7.widget.RecyclerView.onMeasure（RecyclerView.java:3103）在android.view.View.measure（View.java:20151）在 android.support.constraint.ConstraintLayout.internalMeasureChildren（ConstraintLayout.java:934）在 android.support.constraint.ConstraintLayout.onMeasure（ConstraintLayout.java:973）在android.view.View.measure（View.java:20151）在android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:6330）在android.widget.FrameLayout.onMeasure（FrameLayout.java:194）在 android.support.v7.widget.ContentFrameLayout.onMeasure（ContentFrameLayout.java:139）在android.view.View.measure（View.java:20151）在android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:6330）在 android.support.v7.widget.ActionBarOverlayLayout.onMeasure（ActionBarOverlayLayout.java:400）在android.view.View.measure（View.java:20151）在android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:6330）在android.widget.FrameLayout.onMeasure（FrameLayout.java:194）在android.view.View.measure（View.java:20151）在android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:6330）在 android.widget.LinearLayout.measureChildBeforeLayout（LinearLayout.java:1464）在android.widget.LinearLayout.measureVertical（LinearLayout.java:747）在android.widget.LinearLayout.onMeasure（LinearLayout.java:629）在android.view.View.measure（View.java:20151）在android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:6330）在android.widget.FrameLayout.onMeasure（FrameLayout.java:194）在 com.android.internal.policy.PhoneWindow $ DecorView.onMeasure（PhoneWindow.java:3158）在android.view.View.measure（View.java:20151）在android.view.ViewRootImpl.performMeasure（ViewRootImpl.java:2594）在android.view.ViewRootImpl.measureHierarchy（ViewRootImpl.java:1549）在android.view.ViewRootImpl.performTraversals（ViewRootImpl.java:1841）在android.view.ViewRootImpl.doTraversal（ViewRootImpl.java:1437）在 android.view.ViewRootImpl $ TraversalRunnable.run（ViewRootImpl.java:7397）在 android.view.Choreographer $ CallbackRecord.run（Choreographer.java:920）在android.view.Choreographer.doCallbacks（Choreographer.java:695）在android.view.Choreographer.doFrame（Choreographer.java:631）在 android.view.Choreographer $ FrameDisplayEventReceiver.run（Choreographer.java:906）在android.os.Handler.handleCallback（Handler.java:739）在android.os.Handler.dispatchMessage（Handler.java:95）在android.os.Looper.loop（Looper.java:158）在android.app.ActivityThread.main（ActivityThread.java:7224） at java.lang.reflect.Method.invoke（Native Method）在 com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:1230）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:1120）

  public class MyRecyler extends RecyclerView.Adapter<MyRecyler.MyHolder> {
  private Context context;
   private ArrayList<String> names;

    public MyRecyler(Context context, ArrayList<String> names) {
        this.context = context;
        this.names = names;
    }

    @Override
    public MyHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        LayoutInflater inflater = LayoutInflater.from(this.context);
        View view = inflater.inflate(R.layout.names, parent, false);
        return new MyHolder(view);
    }

    @Override
    public void onBindViewHolder(MyHolder holder, int position) {
        holder.name.setText(this.names.get(position));
    }

    @Override
    public int getItemCount() {
        return names.size();
    }

    public class MyHolder extends RecyclerView.ViewHolder {
        TextView name;

        public MyHolder(View itemView) {
            super(itemView);
            name = itemView.findViewById(R.id.name);
        }
    }


    public class MainActivity extends AppCompatActivity {
    public static ArrayList<String> authors_names ;
    RecyclerView recyclerView;
    EditText editText;
    Button button;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        recyclerView = findViewById(R.id.recyclerView);
        // Downloading Data From Internet
        DownloadingData downloadingData = new DownloadingData();
        downloadingData.execute("https://newsapi.org/v1/articles?source=the-next-web&sortBy=latest&apiKey=a301a9e90c774b4ebf7eb21000cdbdef");


        // RecyclerView Set
        MyRecyler recyler = new MyRecyler(MainActivity.this,authors_names);
        recyclerView.setAdapter(recyler);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));
        recyler.notifyDataSetChanged();
    }
}

Answer 1

似乎此代码未正确初始化authors_names。如果我猜错了您的代码逻辑，则需要使用authors_names的结果填充downloadingData。通常，将该列表传递给适配器是一种不好的做法。

我的建议是使用空列表初始化names并定义用于更新其内容的addAll()方法。一个简单且未经优化的实现将是这样的：

private ArrayList<String> names = new ArrayList<>();

public void addAll(ArrayList<String> items) {
    names.clear();
    names.addAll(items);
    notifyDatasetChanged();
}

当addAll()完成其工作时（通常通过回调），您需要在主代码中使用downloadingData方法添加项目。

recyclerView

1 个答案: