setAdapter（）

Question

null指针异常我试图创建一个自定义ListView适配器（大致基于this tutorial，但该示例很简单，我怀疑你需要看看它）。

NewsEntriesAdapter.java

public class NewsEntriesAdapter extends BaseAdapter { 
    private static ArrayList<NewsEntries> newsEntriesArrayList; 

    private final LayoutInflater mInflater; 

    public NewsEntriesAdapter(Context context, ArrayList<NewsEntries> entries) { 
     newsEntriesArrayList = entries; 
     mInflater = LayoutInflater.from(context); 
    } 

    @Override 
    public int getCount() { 
     return newsEntriesArrayList.size(); 
    } 

    @Override 
    public Object getItem(int position) { 
     return newsEntriesArrayList.get(position); 
    } 

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

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

     if (convertView == null) { 
      convertView = mInflater.inflate(R.layout.assignment_list_row_view, 
        null); 
      holder = new ViewHolder(); 
      holder.txtName = (TextView) convertView.findViewById(R.id.name); 
      holder.txtCityState = (TextView) convertView 
        .findViewById(R.id.cityState); 
      holder.txtPhone = (TextView) convertView.findViewById(R.id.phone); 

      convertView.setTag(holder); 
     } else { 
      holder = (ViewHolder) convertView.getTag(); 
     } 

     holder.txtName.setText(newsEntriesArrayList.get(position).getName()); 
     holder.txtCityState.setText(newsEntriesArrayList.get(position) 
       .getCityState()); 
     holder.txtPhone.setText(newsEntriesArrayList.get(position).getPhone()); 

     return convertView; 
    } 

    static class ViewHolder { 
     TextView txtName; 
     TextView txtCityState; 
     TextView txtPhone; 
    } 

} 

MainActivity.java（onCreate方法）

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 

    ArrayList<NewsEntries> results = new ArrayList<NewsEntries>(); 

    // I left the NewsEntries class out of this question; it's just a POJO with some get and set methods for Name, CityState, and Phone 
    NewsEntries sr = new NewsEntries(); 
    sr.setName("Justin Schultz"); 
    sr.setCityState("San Francisco, CA"); 
    sr.setPhone("415-555-1234"); 
    results.add(sr); 

    final ListView lv = (ListView) findViewById(R.id.list); 

    System.out.println(results.get(0).getName()); 

    lv.setAdapter(new NewsEntriesAdapter(this, results)); 
} 

然而，lv.setAdapter线正上方此崩溃与一个空指针异常的应用程序。

任何想法？

Answer 1

您没有在您的Activity中设置任何内容。您的onCreate中没有setContentView或addContentView呼叫。

因此，findViewById将无法​​找到一个看法，因为有没有意见可言，并且将返回null。