我开发了连接到服务器并接收 JSON 响应的应用程序。在此之前它工作正常。但随后它在 ArrayList 中放入 Hashmap 和 HashMap 以显示数据。将 Hashmap 放入 ArrayList 时出错。我的 LogCat 是

    06-03 16:23:10.540: E/AndroidRuntime(15457): FATAL EXCEPTION: AsyncTask #1
06-03 16:23:10.540: E/AndroidRuntime(15457): java.lang.RuntimeException: An error occured while executing doInBackground()
06-03 16:23:10.540: E/AndroidRuntime(15457):    at android.os.AsyncTask$3.done(AsyncTask.java:278)
06-03 16:23:10.540: E/AndroidRuntime(15457):    at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
06-03 16:23:10.540: E/AndroidRuntime(15457):    at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
06-03 16:23:10.540: E/AndroidRuntime(15457):    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
06-03 16:23:10.540: E/AndroidRuntime(15457):    at java.util.concurrent.FutureTask.run(FutureTask.java:137)
06-03 16:23:10.540: E/AndroidRuntime(15457):    at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:208)
06-03 16:23:10.540: E/AndroidRuntime(15457):    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
06-03 16:23:10.540: E/AndroidRuntime(15457):    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
06-03 16:23:10.540: E/AndroidRuntime(15457):    at java.lang.Thread.run(Thread.java:856)
06-03 16:23:10.540: E/AndroidRuntime(15457): Caused by: java.lang.NullPointerException
06-03 16:23:10.540: E/AndroidRuntime(15457):    at com.example.project.MainActivity$LoadAllProducts.doInBackground(MainActivity.java:498)
06-03 16:23:10.540: E/AndroidRuntime(15457):    at com.example.project.MainActivity$LoadAllProducts.doInBackground(MainActivity.java:1)
06-03 16:23:10.540: E/AndroidRuntime(15457):    at android.os.AsyncTask$2.call(AsyncTask.java:264)
06-03 16:23:10.540: E/AndroidRuntime(15457):    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
06-03 16:23:10.540: E/AndroidRuntime(15457):    ... 5 more

我的类(class)是

public class asasa extends Activity  {
    //ListView listView;
    Intent intent;
    public int currentimageindex=0;
    private ProgressDialog pDialog;

    Timer timer;
    TimerTask task;
    ImageView slidingimage;

    ProgressDialog progressDialog;


    // Creating JSON Parser object
    JSONParser jParser = new JSONParser();

    static final String URL = "http://172.20.55.175/android_connect/get_all_products.php";

    private static final String TAG_SUCCESS = "success";
    private TextView mStatusView;
    private EditText searchEditText;


    private static final String TAG_PRODUCTS = "products";
    private static final String TAG_NAME = "name";
    private static final String TAG_Description = "description";
    private static final String TAG_URL = "url";
    private static final String TAG_Price = "price";


    ListView list;
    LazyAdapter adapter;
    // flag for Internet connection status
    Boolean isInternetPresent = false;

    // products JSONArray

    JSONArray products = null;

    // Connection detector class
    ConnectionDetector cd;



    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        cd = new ConnectionDetector(getApplicationContext());

        // get Internet status
        isInternetPresent = cd.isConnectingToInternet();

        if (isInternetPresent) {
            LoadAllProducts il = new LoadAllProducts();
            il.execute(URL);
        }
        else
        {
            // Internet connection is not present
            // Ask user to connect to Internet
            Toast.makeText(asasa.this, "No Internet Connection You don't have internet connection.", Toast.LENGTH_LONG).show();
        }

    }
    public void longToast(CharSequence message) {
        Toast.makeText(this, message, Toast.LENGTH_LONG).show();
    }



    public class LazyAdapter extends BaseAdapter {

        private Activity activity;
        private ArrayList<HashMap<String, String>> data;
        private  LayoutInflater inflater=null;
        public ImageLoader imageLoader; 

        public LazyAdapter(Activity a, ArrayList<HashMap<String, String>> d) {
            activity = a;
            data=d;
            inflater = (LayoutInflater)activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            imageLoader=new ImageLoader(activity.getApplicationContext());
        }

        public int getCount() {
            return data.size();
        }

        public Object getItem(int position) {
            return position;
        }

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

        public View getView(int position, View convertView, ViewGroup parent) {
            View vi=convertView;
            if(convertView==null)
                vi = inflater.inflate(R.layout.list_row, null);

            TextView title = (TextView)vi.findViewById(R.id.title); // title
            TextView artist = (TextView)vi.findViewById(R.id.artist); // artist name
            TextView duration = (TextView)vi.findViewById(R.id.duration); // duration
            ImageView thumb_image=(ImageView)vi.findViewById(R.id.list_image); // thumb image

            HashMap<String, String> song = new HashMap<String, String>();
            song = data.get(position);

            // Setting all values in listview
            title.setText(song.get(asasa.TAG_NAME));
            artist.setText(song.get(asasa.TAG_Description));
            duration.setText(song.get(asasa.TAG_Price));
            imageLoader.DisplayImage(song.get(asasa.TAG_URL), thumb_image);
            return vi;
        }
    }






    class LoadAllProducts extends AsyncTask<String, String, String> {
        // creating new HashMap
        ArrayList<HashMap<String, String>> productsList;



        /**
         * Before starting background thread Show Progress Dialog
         * */
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            pDialog = new ProgressDialog(asasa.this);
            pDialog.setMessage("Loading products. Please wait...");
            pDialog.setIndeterminate(false);
            pDialog.setCancelable(false);
            pDialog.show();
        }

        /**
         * getting All products from url
         * */
        protected String doInBackground(String... args) {
            // Building Parameters
            List<NameValuePair> params = new ArrayList<NameValuePair>();
            HashMap<String, String> map = new HashMap<String, String>();

            // getting JSON string from URL
            JSONObject json = jParser.makeHttpRequest(URL, "GET", params);

            // Check your log cat for JSON reponse

            try {
                // Checking for SUCCESS TAG
                int success = json.getInt(TAG_SUCCESS);

                if (success == 1) {
                    // products found
                    // Getting Array of Products
                    products = json.getJSONArray(TAG_PRODUCTS);
                    // looping through All Products
                    for (int i = 0; i < products.length()-1; i++) {
                        JSONObject c = products.getJSONObject(i);

                        String name = c.getString(TAG_NAME);
                        String description = c.getString(TAG_Description);
                        String URl = c.getString(TAG_URL);
                        String price = c.getString(TAG_Price);



                        // adding each child node to HashMap key => value
                        map.put(TAG_NAME, name);
                        map.put(TAG_Description, description);
                        map.put(TAG_URL, URl);
                        map.put(TAG_Price, price);

                        // adding HashList to ArrayList
                        productsList.add(map);

                    }
                } else {
                    // no products found
                    // Launch Add New product Activity

                }
            } catch (JSONException e) {
                e.printStackTrace();
            }

            return null;
        }

        /**
         * After completing background task Dismiss the progress dialog
         * **/
        protected void onPostExecute(String file_url) {
            // dismiss the dialog after getting all products
            list=(ListView)findViewById(R.id.list);

            // Getting adapter by passing xml data ArrayList
            adapter=new LazyAdapter(asasa.this, productsList);        
            list.setAdapter(adapter);




        }

    }


    public void onPause()
    {
        super.onPause();
        if (progressDialog.isShowing()) {
            progressDialog.dismiss();
            // progressDialog.setCancelable(true);
        }

    }

}

第498行是

productsList.add(map);

在 protected 字符串中 doInBackground(String... args)

我无法弄清楚错误...为什么会发生。它成功返回 json 响应但可以放入 hashmap

最佳答案

你还没有初始化你的

ArrayList<HashMap<String, String>> productsList;

在使用前对其进行初始化。

ArrayList<HashMap<String, String>> productsList = new ArrayList<HashMap<String, String>>();

关于android - java.lang.NullPointerException in doInBackground put HashMap in ArrayList，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/16895874/