Question

    `Adapter class :::


    public class YAdapter extends ArrayAdapter<String> {

        ArrayList<String> items;
        Context context;
        private LayoutInflater mInflater;

        static class ViewHolder {
            TextView yName;
        }

        public YAdapter(Context context,ArrayList<String> items) {
            super(context, R.layout.single_item_list_row, items);
            this.context=context;
            mInflater = LayoutInflater.from(context);
            this.items = items;
        }

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

        @Override
        public String getItem(int arg0) {
            return items.get(arg0);
        }

        @Override
        public long getItemId(int arg0) {
            return arg0;
        }





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

    if(convertView == null) {
        convertView = Inflater.inflate(R.layout.single_item_list_row,null);
        holder = new ViewHolder();
        holder.yName=(TextView)convertView.findViewById(R.id.text1);
        convertView.setTag(holder);
           } 
                else {
                    holder = (ViewHolder) convertView.getTag();
                }
                try
                {
                    if(items.get(position) != null)
                        holder.yName.setText(items.get(position));  
                }
                catch (Exception e) {
                      Log.e("ERROR","Adapter error in generating view);
                }
                return convertView;
            }

        }

        Activity Class ::



        public class DemoActivity extends Activity {


            ListView listView;
            ArrayList<String> temp = new ArrayList<String>();
            YAdapter adapter;

            @Override
            public void onCreate(Bundle savedInstanceState) {
                super.onCreate(savedInstanceState);
                setContentView(R.layout.main);
    listView = (ListView) findViewById(R.id.list);


            }
                @Override
            public void onResume() {
                super.onResume();
                temp.add("one");
                temp.add("two");
                temp.add("three");
                temp.add("four");
                adapter = new YAdapter(DemoActivity.this , temp);


                **listView.setAdapter(adapter);**  -- exception

            }
            }

    listView.setAdapter(adapter);

this line causes an exception.

当我尝试将适配器设置为列表时，如果我删除此行没有显示错误，并且屏幕上没有组件显示只显示黑屏，则会出错。

我编码的内容如下所示bt我得到空指针异常。请告诉我我错过了什么？

Answer 1

查看此行，您的活动名称

public class Activity extends Activity {

并在适配器行

 adapter = new YAdapter(YellowPagesActivity.this , temp);

那么什么是 YellowPagesActivity.this ？

Answer 2

使用@ViewById(R.id.list) so no need to findViewById .....

问题到期

adapter = new YAdapter(YellowPagesActivity.this , temp);

NullPointer为ListView设置适配器时出现异常

2 个答案: