php - 在 AsyncTask 中执行 doInBackground() 时出错

Question

您好，我正在使用 AsyncTask 从 php 文件中获取数据，但是当我运行该应用程序时出现此错误!

List<Online_Messages_item> o;
public class RequestPostsTask extends AsyncTask<Void, Void, Boolean> {
        ProgressDialog pdLoading;


        @Override
        protected void onPreExecute() {
            pdLoading = new ProgressDialog(Messages_online.this);
            pdLoading.setProgressStyle(ProgressDialog.STYLE_SPINNER);
            pdLoading.setMessage("please wait ...");
            pdLoading.setIndeterminate(false);
            pdLoading.setCancelable(false);
            pdLoading.show();
        }

        @Override
        protected Boolean doInBackground(Void... params) {
            boolean status = false; 
            HttpURLConnection urlConnection = null;

            try {
                URL url = new URL("my url");

                urlConnection = (HttpURLConnection) url.openConnection();
                Charset charset = Charset.forName("UTF8");
                int responseCode = urlConnection.getResponseCode();

                if (responseCode == HttpURLConnection.HTTP_OK) {
                    BufferedReader in = new BufferedReader(new InputStreamReader(urlConnection.getInputStream(), charset));
                    if (in != null) {
                        StringBuilder strBuilder = new StringBuilder();
                        int ch = 0;
                        while ((ch = in.read()) != -1)
                            strBuilder.append((char) ch);
                        String response = strBuilder.toString();
                        Log.d("Server response:", response);

                        JSONObject jObject = new JSONObject(response);
                        JSONArray jsonArray = jObject.getJSONArray("posts");
                        for(int i=0; i<jsonArray.length(); i++){
                            Online_Messages_item omi = new Online_Messages_item();
                            omi.setId(jsonArray.getJSONObject(i).getLong("ID"));
                            omi.settext(jsonArray.getJSONObject(i).getString("Text"));
                            omi.setlikes(jsonArray.getJSONObject(i).getString("Likes"));
                            omi.setpt(jsonArray.getJSONObject(i).getString("PublishTime"));
                            o.add(omi);
                        }
                        if(o.size() >= 1)
                            status = true;
                    }

                    in.close();
                }
            }
            catch(MalformedURLException e){
                e.printStackTrace();
            }
            catch (IOException e) {
                e.printStackTrace();
            }
            catch (JSONException e) {
                e.printStackTrace();
            }
            finally {
                urlConnection.disconnect();
            }

            return status;
        }

        @Override
        protected void onPostExecute(Boolean result) {
            BaseAdapter ba=new Messages_online_adapter(Messages_online.this,o);
            listView.setAdapter(ba);
            pdLoading.dismiss();

        }
    }

这是日志

03-13 08:12:05.111: E/AndroidRuntime(1232): FATAL EXCEPTION: AsyncTask #1 03
-13 08:12:05.111: E/AndroidRuntime(1232): java.lang.RuntimeException: An error occured while executing doInBackground()
03-13 08:12:05.111: E/AndroidRuntime(1232):     at android.os.AsyncTask$3.done(AsyncTask.java:299)
03-13 08:12:05.111: E/AndroidRuntime(1232):     at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
03-13 08:12:05.111: E/AndroidRuntime(1232):     at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
03-13 08:12:05.111: E/AndroidRuntime(1232):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
03-13 08:12:05.111: E/AndroidRuntime(1232):     at java.util.concurrent.FutureTask.run(FutureTask.java:137)
03-13 08:12:05.111: E/AndroidRuntime(1232):     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
03-13 08:12:05.111: E/AndroidRuntime(1232):     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
03-13 08:12:05.111: E/AndroidRuntime(1232):     at java.lang.Thread.run(Thread.java:856)
03-13 08:12:05.111: E/AndroidRuntime(1232): Caused by: java.lang.NullPointerException
03-13 08:12:05.111: E/AndroidRuntime(1232):     at mr.zereshk.online.Messages_online$RequestPostsTask.doInBackground(Messages_online.java:80)
03-13 08:12:05.111: E/AndroidRuntime(1232):     at mr.zereshk.online.Messages_online$RequestPostsTask.doInBackground(Messages_online.java:1)
03-13 08:12:05.111: E/AndroidRuntime(1232):     at android.os.AsyncTask$2.call(AsyncTask.java:287)
03-13 08:12:05.111: E/AndroidRuntime(1232):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
03-13 08:12:05.111: E/AndroidRuntime(1232):     ... 4 more

有什么帮助吗？提前致谢!

Answer 1

List<Online_Messages_item> o;

你永远不会初始化 o .

你应该把 o = new ArrayList<Online_Messages_item>(); 放在哪里.我建议构造函数