Question

我正在尝试从JSON响应生成列表视图但无法执行此操作。在线获取错误：“list_view.setAdapter（customAdapter）;” @onPostExecute

上面一行的NullPointerException ...

完整代码：

public class Screen2 extends AppCompatActivity {
    ProgressDialog pDialog;
    ArrayList<Information> record_list;
    ListView list_view;
    CustomAdapter customAdapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.screen2);
        record_list=new ArrayList<Information>();
        list_view=(ListView) findViewById(R.id.list_view);
        new Test().execute();
    }

    public class Test extends AsyncTask<String, Void, ArrayList<Information>> {
        @Override
        protected void onPreExecute() {

            super.onPreExecute();

            // Showing progress dialog
            pDialog = new ProgressDialog(Screen2.this);
            pDialog.setMessage("Please wait...");
            pDialog.setCancelable(false);
            pDialog.show();
        }

        @Override
        protected ArrayList<Information> doInBackground(String... params) {
            if(record_list.size()>0){record_list.clear();}
            String jsonStr = makeServiceCall();
            //ssen = new ArrayList<Information>();
            try {
                //HashMap<String,String> hashMap=new HashMap<>();
                JSONArray jsonArray=new JSONArray(jsonStr);
                for(int i=0;i<jsonArray.length();i++) {
                    JSONObject jsonObject = jsonArray.getJSONObject(i);
                    String id = jsonObject.getString("id");
                    String name = jsonObject.getString("label");
                    String email = jsonObject.getString("email");
                    Information information = new Information(id, name, email);
                    System.out.println("id: " + id + "name:" + name + "email" + email);
                    record_list.add(information);
                }
                System.out.println(jsonStr);
                return record_list;
                //return record_list;
            } catch (JSONException e) {
                e.printStackTrace();
            }

            return null;
        }

        @Override
        protected void onPostExecute(ArrayList<Information> s) {
            super.onPostExecute(s);
            for(int i=0;i<record_list.size();i++){
                System.out.println(record_list.get(i));
            }
            if(record_list!=null && !record_list.isEmpty()){
                customAdapter=new CustomAdapter(Screen2.this,record_list);
                list_view.setAdapter(customAdapter);
            }
            else {
                Toast.makeText(Screen2.this, "Array List is Empty", Toast.LENGTH_SHORT).show();
            }

            //ListAdapter listAdapter1=new ArrayAdapter<String>(Screen2.this,R.layout.custom_row,record_list);
            //list_view.setAdapter(listAdapter);
            if (pDialog.isShowing())
                pDialog.dismiss();

            /**
             * Updating parsed JSON data into ListView
             * */
        }

        public String makeServiceCall(){
            String response = null;
            try {
                URL url = new URL("http://192.168.1.127:9000/tasks2");
                HttpURLConnection conn = (HttpURLConnection) url.openConnection();
                conn.setRequestMethod("GET");
                // read the response
                InputStream in = new BufferedInputStream(conn.getInputStream());
                response = convertStreamToString(in);
            } catch (MalformedURLException e) {
                System.out.println("MalformedURLException: " + e.getMessage());
            } catch (ProtocolException e) {
                System.out.println("MalformedURLException: " + e.getMessage());
            } catch (IOException e) {
                System.out.println("MalformedURLException: " + e.getMessage());
            } catch (Exception e) {
                System.out.println("MalformedURLException: " + e.getMessage());
            }
            return response;
        }

        private String convertStreamToString(InputStream is) {
            BufferedReader reader = new BufferedReader(new InputStreamReader(is));
            StringBuilder sb = new StringBuilder();

            String line;
            try {
                while ((line = reader.readLine()) != null) {
                    sb.append(line).append('\n');
                }
            } catch (IOException e) {
                e.printStackTrace();
            } finally {
                try {
                    is.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            System.out.println(sb);
            return sb.toString();
        }
    }
}

请浏览堆栈跟踪以获取上述代码... 如果有人解决了这个问题，对我来说非常有帮助。

E/AndroidRuntime: FATAL EXCEPTION: main
java.lang.NullPointerException
at com.example.hariprasad.healthpassportnew1.Screen2$Test.onPostExecute(Screen2.java:99)
at com.example.hariprasad.healthpassportnew1.Screen2$Test.onPostExecute(Screen2.java:51)
at android.os.AsyncTask.finish(AsyncTask.java:631)
at android.os.AsyncTask.access$600(AsyncTask.java:177)
at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:644)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4960)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1038)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:805)
at dalvik.system.NativeStart.main(Native Method)

Answer 1

也许您的record_list为空所以请添加

 if (record_list.size > 0) {
  list_view.setAdapter(customAdapter);
 }

以及在record_list中添加数据之前清楚

将此代码放在String jsonStr = makeServiceCall();

之前

  if (record_list.size > 0) {
   record_list.clear();
  }

E / AndroidRuntime：FATAL EXCEPTION：main java.lang.NullPointerException列表视图

1 个答案: