尝试在空对象引用上调用 Adapter.notifyDataSetChanged()'

Question

我也尝试在 onCreate() 中添加适配器，但它会引发空指针异常，并显示错误“尝试在空对象引用上调用 listVIew.setAdapter。

这是我在 Main Activity 中使用 notifyDataSetChange() 的代码；

import static com.name.sample.Tab1.adapter;


public class Requests extends AsyncTask<String, Void, String> {

    @Override
    protected String doInBackground(String... params) {

        Cursor c =  myDB.rawQuery("SELECT * FROM requests", null);

        int aIndex = c.getColumnIndex("name");
        int bIndex = c.getColumnIndex("nick");
        int cIndex = c.getColumnIndex("num");

        name.clear();
        nick.clear();
        number.clear();

        if (c.moveToFirst()){

            do {

                name.add(c.getString(aIndex));
                nick.add(c.getString(bIndex));
                number.add(c.getInt(cIndex));

            } while (c.moveToNext());
        }

        return null;
    }

    @Override
    protected void onPostExecute(String s) {
        super.onPostExecute(s);


        adapter.notifyDataSetChanged();


    }
}

这是我的 Tab1 代码 这是适配器的代码

public class Tab1 extends Fragment {

static ListView listNotifications;
final static ArrayList<String> name = new ArrayList<>();
static ArrayList<Integer> number = new ArrayList<>();
static ArrayList<String> nick = new ArrayList<>();

static ImageAdapter adapter;


public static class ImageAdapter extends ArrayAdapter<String> {
    private final Context context;
    private final String[] values;

    public ImageAdapter (Context context, String[] values) {
        super(context, R.layout.list_with_icons, values);
        this.context = context;
        this.values = values;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {

        LayoutInflater inflater = (LayoutInflater) context
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);

        View rowView = inflater.inflate(R.layout.list_with_icons, parent, false);

        TextView textView = (TextView) rowView.findViewById(R.id.textViewName);

        ImageView imageView = (ImageView) rowView.findViewById(R.id.imagePicture);

        textView.setText(values[position]);
        // Change the icon for Windows and iPhone


        return rowView;
    }
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {

    View rootView = inflater.inflate(R.layout.tab1layout, container, false);

    String[] nameString = new String[name.size()];
    nameString = name.toArray(nameString);

    adapter = new ImageAdapter (getActivity(), nameString);



   listNotifications =(ListView)rootView.findViewById(R.id.listNotifications);

listNotifications.setAdapter(adapter);




    return rootView;


}}

Answer 1

尝试使用：adapterClass.this.notifyDataSetChanged() in onPostExcecute()

 @Override
protected void onPostExecute(String s) {
    super.onPostExecute(s);
    InvitedAdapter.this.notifyDataSetChanged();
}

Answer 2

您在列表视图中添加了错误的适配器。在 onCreateView() 中应该是这样的：

listNotifications.setAdapter(adapter);

试试这个:)