Question

我有一个主要活动，在用户打开应用时加载三个标签。所有选项卡都有从外部数据库填充的ListView，因此下载和显示所有内容需要几秒钟。当然，您无需等待下载所有数据即可使用该应用程序。

有时，我在这一行得到一个NullPointerException：

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

这似乎只有在我下载所有内容之前退出应用程序时才会发生，但并非总是如此，例如3个中的1个。但是，这可能不对，因为如下所示，我检查是否有任何数据在调用适配器之前下载，结果总是相同的大小（7），这意味着下载成功，但由于某种原因，LayoutInflater变为null。

DownloadAsynctask：

public class DownloadNewsfeed extends AsyncTask<String, Void, ArrayList<String>> {

        @Override
        protected void onPostExecute(ArrayList<String> result) {            

            Log.i("SIZE", result.size() + "");
            if (result.size() == 0) {
                (...)
            } else {
                myadapter = new MyAdapter(getActivity(), arr_userid, arr_event, arr_subject, arr_date, arr_result, arr_username, arr_photo, arr_timediff);
                lv.setAdapter(myadapter);
            }
        }

@Override
        protected void onPreExecute() { 
          (...)
          return arr_userid;
        }

@Override
        protected ArrayList<String> doInBackground(String... params) {
            (...)
      }
    }

适配器

public class MyAdapter extends BaseAdapter
    {

        public Context context;
        ArrayList<String> arr_userid = new ArrayList<String>();
        ArrayList<String> arr_event = new ArrayList<String>();
        ArrayList<String> arr_subject = new ArrayList<String>();
        ArrayList<String> arr_date = new ArrayList<String>();
        ArrayList<String> arr_result = new ArrayList<String>();
        ArrayList<String> arr_username = new ArrayList<String>();
        ArrayList<String> arr_photo = new ArrayList<String>();
        ArrayList<String> arr_timediff = new ArrayList<String>();

        public LayoutInflater inflater;

        public MyAdapter(Context context, ArrayList<String> arr_userid, ArrayList<String> arr_event, ArrayList<String> arr_subject, 
                ArrayList<String> arr_date, ArrayList<String> arr_result, ArrayList<String> arr_username, ArrayList<String> arr_photo,
                 ArrayList<String> arr_timediff) {
            super();

            this.context = context;
            this.arr_userid = arr_userid;
            this.arr_event = arr_event;
            this.arr_subject = arr_subject;
            this.arr_date = arr_date;
            this.arr_result = arr_result;
            this.arr_username = arr_username;
            this.arr_photo = arr_photo;
            this.arr_timediff = arr_timediff;

            this.inflater = (LayoutInflater)context.getSystemService(Context.LAYOUT_INFLATER_SERVICE); //**NULLPOINTER**
        }

        @Override
        public int getCount() {
            // TODO Auto-generated method stub
            return arr_userid.size();
        }

        @Override
        public Object getItem(int position) {
            // TODO Auto-generated method stub
            return null;
        }

        @Override
        public long getItemId(int position) {
            // TODO Auto-generated method stub
            return 0;
        }

        public class ViewHolder
        {
            ImageView image;
            TextView tv_name, tv_date, tv_text, tv_text2;
            LinearLayout row;
        }

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

            final ViewHolder holder;
            if(convertView==null)
            {
                holder = new ViewHolder();
                convertView = inflater.inflate(R.layout.newsfeed_listitem_new, null);

                holder.image = (ImageView) convertView.findViewById(R.id.iv_user);
                holder.tv_text = (TextView) convertView.findViewById(R.id.tv_text);
                holder.tv_text2 = (TextView) convertView.findViewById(R.id.tv_text2);
                holder.tv_name = (TextView) convertView.findViewById(R.id.tv_name);
                holder.tv_date = (TextView) convertView.findViewById(R.id.tv_date);
                holder.row = (LinearLayout) convertView.findViewById(R.id.lineItem);

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

                holder.tv_text.setText(arr_event.get(position) + ":");
                holder.tv_text2.setText(arr_result.get(position));

            return convertView;
        }
    }

Answer 1

退出应用后，再做任何工作都没有意义。活动销毁后getActivity()将返回null。在继续之前执行空检查：

@Override
protected void onPostExecute(ArrayList<String> result) {            
    if (getActivity() == null) {
        Log.e(getClass().getSimpleName(), "Activity ended prematurely.");
        return;
    }

    Log.i("SIZE", result.size() + "");
    if (result.size() == 0) {
        (...)
    } else {
        myadapter = new MyAdapter(getActivity(), arr_userid, arr_event, arr_subject, arr_date, arr_result, arr_username, arr_photo, arr_timediff);
        lv.setAdapter(myadapter);
    }
}

无关注意：请考虑为新闻源项目创建一个持有者，例如：

public class NewsfeedItem {
    String userid;
    String event;
    String subject;
    String date;
    String result;
    String username;
    String photo;
    String timediff;

    public NewsfeedItem() {}
}

这将使您免于获得大量ArrayList s而只支持一个。

NullPointerException on（LayoutInflater）context.getSystemService（Context.LAYOUT_INFLATER_SERVICE）;

1 个答案: