我的Android有致命的错误

Question

我正在尝试从数据库(phpmyadmin(获取我的数据，然后将其转换为JSON，将其放入ListView或TextView中，但是当我运行应用程序时，当我关闭应用程序时，请检查日志i i时找到一个例外。

这是我的代码：

mainActivity.java

public class MainActivity extends AppCompatActivity {
ProgressDialog pDialog;
// Creating JSON Parser object
ListView lv;
ArrayList<HashMap<String, String>> productsList;
// url to get all products list
private static String url_all_products = "http://192.168.0.100/takeofftravel/test.php";
// products JSONArray
JSONArray products = null;
int error=0;
// JSON Node names
private static final String TAG_SUCCESS = "success";
private static final String TAG_NOTIF = "notif";
private static final String TAG_PID = "id";
private static final String TAG_Type = "type";
private static final String TAG_REQUETE = "requete";
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    // Hashmap for ListView.
    productsList = new ArrayList<HashMap<String, String>>();
    // Get listview
    lv = (ListView)findViewById(R.id.listView);
    // Loading products in Background Thread
    new LoadAllProducts().execute();

    // on seleting single product
    // launching Edit Product Screen
    lv.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view,
                                int position, long id) {
  /*          HashMap<String,String> map=new HashMap<String, String>();
            map=(HashMap<String,String>)lv.getAdapter().getItem(position);
            String ide=map.get(TAG_PID);
            Toast.makeText(All.this,ide,Toast.LENGTH_LONG).show();
            Intent i=new Intent(getApplicationContext(),Detail.class);
            i.putExtra("id",ide);
            startActivity(i);
            finish();*/
        }
    });
}

class LoadAllProducts extends AsyncTask<String, String, String> {
    /**
     * Before starting background thread Show Progress Dialog
     * */
    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        pDialog = new ProgressDialog(MainActivity.this);
        pDialog.setMessage("Loading...");
        pDialog.setIndeterminate(false);
        pDialog.setCancelable(false);
        pDialog.show();
    }
    /**
     * getting All products from url
     * */
    protected String doInBackground(String... args) {
        // Building Parameters
        HashMap<String, String> params = new HashMap<String, String>();
        JSONParser jParser = new JSONParser();
        // getting JSON string from URL
        JSONObject json = jParser.makeHttpRequest(url_all_products, "GET", params);
        // Check your log cat for JSON reponse
        Log.d("All Products: ", json.toString());



        // Checking for SUCCESS TAG
        int success = 0;
        try {
            success = json.getInt(TAG_SUCCESS);
            if (success == 1) {
                // products found
                // Getting Array of Products
                products = json.getJSONArray(TAG_NOTIF);
                // looping through All Products
                for (int i = 0; i < products.length(); i++) {
                    JSONObject c = products.getJSONObject(i);
                    // Storing each json item in variable
                    String id = c.getString(TAG_PID);
                    String type = c.getString(TAG_Type);
                    String requete=c.getString(TAG_REQUETE);
                    // creating new HashMap
                    HashMap<String, String> map = new HashMap<String, String>();
                    // adding each child node to HashMap key => value
                    map.put(TAG_PID, id);
                    map.put(TAG_Type, type);
                    map.put(TAG_REQUETE,requete);
                    // adding HashList to ArrayList
                    productsList.add(map);
                }
            } else {
            }
        } 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
        pDialog.dismiss();
        // updating UI from Background Thread
        //    runOnUiThread(new Runnable() {
        //       public void run() {
        /**
         * Updating parsed JSON data into ListView
         * */
        ListAdapter adapter = new SimpleAdapter(
                MainActivity.this, productsList,
                R.layout.item, new String[] { TAG_PID,
                TAG_Type,TAG_REQUETE},
                new int[] { R.id.pid, R.id.nom,R.id.nature });
        // updating listview
        lv.setAdapter(adapter);
        //  }
        // });
    }
}

}

jsonparse.java文件：

public class JSONParser {
String charset = "UTF-8";
HttpURLConnection conn;
DataOutputStream wr;
StringBuilder result;
URL urlObj;
JSONObject jObj = null;
StringBuilder sbParams;
String paramsString;
public JSONObject makeHttpRequest(String url, String method,
                                  HashMap<String, String> params) {
    sbParams = new StringBuilder();
    int i = 0;
    for (String key : params.keySet()) {
        try {
            if (i != 0){
                sbParams.append("&");
            }
            sbParams.append(key).append("=")
                    .append(URLEncoder.encode(params.get(key), charset));
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        }
        i++;
    }
    if (method.equals("POST")) {
        // request method is POST
        try {
            urlObj = new URL(url);
            conn = (HttpURLConnection) urlObj.openConnection();
            conn.setDoOutput(true);
            conn.setRequestMethod("POST");
            conn.setRequestProperty("Accept-Charset", charset);
            conn.setReadTimeout(10000);
            conn.setConnectTimeout(15000);
            conn.connect();
            paramsString = sbParams.toString();
            wr = new DataOutputStream(conn.getOutputStream());
            wr.writeBytes(paramsString);
            wr.flush();
            wr.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    else if(method.equals("GET")){
        // request method is GET
        if (sbParams.length() != 0) {
            url += "?" + sbParams.toString();
        }
        try {
            urlObj = new URL(url);
            conn = (HttpURLConnection) urlObj.openConnection();
            conn.setDoOutput(false);
            conn.setRequestMethod("GET");
            conn.setRequestProperty("Accept-Charset", charset);
            conn.setConnectTimeout(15000);
            conn.connect();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    try {
        //Receive the response from the server
        InputStream in = new BufferedInputStream(conn.getInputStream());
        BufferedReader reader = new BufferedReader(new InputStreamReader(in));
        result = new StringBuilder();
        String line;
        while ((line = reader.readLine()) != null) {
            result.append(line);
        }
        Log.d("JSON Parser", "result: " + result.toString());
    } catch (IOException e) {
        e.printStackTrace();
    }
    conn.disconnect();
    // try parse the string to a JSON object
    try {
        jObj = new JSONObject(result.toString());
    } catch (JSONException e) {
        Log.e("JSON Parser", "Error parsing data " + e.toString());
    }
    // return JSON Object
    return jObj;
}

}

错误消息：

E/AndroidRuntime: FATAL EXCEPTION: AsyncTask #1
              Process: com.example.asus.json, PID: 11657
              java.lang.RuntimeException: An error occured while executing doInBackground()
                  at android.os.AsyncTask$3.done(AsyncTask.java:300)
                  at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355)
                  at java.util.concurrent.FutureTask.setException(FutureTask.java:222)
                  at java.util.concurrent.FutureTask.run(FutureTask.java:242)
                  at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
                  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
                  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
                  at java.lang.Thread.run(Thread.java:841)
               Caused by: java.lang.NullPointerException
                  at com.example.asus.json.JSONParser.makeHttpRequest(JSONParser.java:124)
                  at com.example.asus.json.MainActivity$LoadAllProducts.doInBackground(MainActivity.java:100)
                  at com.example.asus.json.MainActivity$LoadAllProducts.doInBackground(MainActivity.java:75)
                  at android.os.AsyncTask$2.call(AsyncTask.java:288)
                  at java.util.concurrent.FutureTask.run(FutureTask.java:237)
                  at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231) 
                  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112) 
                  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587) 
                  at java.lang.Thread.run(Thread.java:841) 

Answer 1

主要问题是在第124行的JSONPARSER类中进行。这是在发生JSONPARSER类，因为JSONPARSER类没有返回任何JSON，并且由此产生的JSON为NULL，您正在调用函数getint((null JSON对象，这就是为什么NullPoInterException。