java - ListAdapter 的奇怪 NullPointerException

Question

好吧，所以我创建了一个 ListView 和我自己的 ListAdapter，但是每当我将结果添加到 ListAdapter 时，它都会崩溃，并显示 NullPointerException

当 filldata() 打开时，我确实启动了 Adapter MyAdapter adapter = new MyAdapter ();

我的代码:

     public void filldata() throws IOException{
        MyAdapter adapter = new MyAdapter ();

        for (int i = 1; i <= 10; i++) {

            AdapterItem test = new AdapterItem(1+i, 2+i, 3+i);

            adapter.addAdapterItem(test);
        }

        setListAdapter(adapter);

    }
}

public class MyAdapter extends BaseAdapter {
    private List<AdapterItem> items;

    public void addAdapterItem(AdapterItem item) {
        items.add(item);
    }

    public int getCount() {
      return items.size();
    }

    public Object getItem(int position) {
      return items.get(position);
    }

    @Override
    public long getItemId(int position) {
            return position;
    }

    public View getView(int position, View convertView, ViewGroup parent){
      View rowView = getLayoutInflater().inflate(R.layout.searchitemview, parent);
      TextView firstTextView = (TextView) rowView.findViewById(R.id.txtTitle);
      firstTextView.setText(items.get(position).first);
      // do the same with second and third
      return rowView;
    }
}

class AdapterItem {
    public String first;
    public String second;
    public String third;

    public AdapterItem(String first, String second, String third) {
        this.first = first;
        this.second = second;
        this.third = third;
    }
}

当它到达adapter.addAdapterItem(test);时它崩溃了

Answer 1

在MyAdapter构造函数中初始化items。当您尝试添加项目时，它为 null，因此出现异常

items = new ArrayList<AdapterItem>();