Android AsyncTask＆lt;＆gt; doInBackground（）抛出异常

Question

我正在尝试使用Json Parsing从网络服务器（wamp）发送和接收数据。在代码中我使用AsynTask来获取json对象及其响应。但它给了我错误。这是代码

public class NewProductActivity extends Activity {

    // Progress Dialog
    private ProgressDialog pDialog;

    JSONParser jsonParser = new JSONParser();
    EditText inputName;
    EditText inputPrice;
    EditText inputDesc;

    // url to create new product
    private static String url_create_product = "http://10.0.2.2/android_connect/create_product.php";

    // JSON Node names
    private static final String TAG_SUCCESS = "success";

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.add_product);




        // Edit Text
        inputName = (EditText) findViewById(R.id.inputName);
        inputPrice = (EditText) findViewById(R.id.inputPrice);
        inputDesc = (EditText) findViewById(R.id.inputDesc);

        // Create button
        Button btnCreateProduct = (Button) findViewById(R.id.btnCreateProduct);

        // button click event
        btnCreateProduct.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View view) {
                // creating new product in background thread
                new CreateNewProduct().execute();
            }
        });
    }

    /**
     * Background Async Task to Create new product
     * */
    class CreateNewProduct extends AsyncTask<String, String, String>  {


         /* Before starting background thread Show Progress Dialog
         * */
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            pDialog = new ProgressDialog(NewProductActivity.this);
            pDialog.setMessage("Creating Product..");
            pDialog.setIndeterminate(false);
            pDialog.setCancelable(true);
            pDialog.show();
        }

        /**
         * Creating product
         * */
        protected String doInBackground(String... args) {
            String name = inputName.getText().toString();
            String price = inputPrice.getText().toString();
            String description = inputDesc.getText().toString();

            // Building Parameters
            List<NameValuePair> params = new ArrayList<NameValuePair>();
            params.add(new BasicNameValuePair("name", name));
            params.add(new BasicNameValuePair("price", price));
            params.add(new BasicNameValuePair("description", description));

            // getting JSON Object
            // Note that create product url accepts POST method
            JSONObject json = jsonParser.makeHttpRequest(url_create_product,
                    "POST", params);

            // check log cat fro response
            Log.d("Create Response", json.toString());

            // check for success tag
            try {
                int success = json.getInt(TAG_SUCCESS);

                if (success == 1) {
                    // successfully created product
                    Intent i = new Intent(getApplicationContext(), AllProductsActivity.class);
                    startActivity(i);

                    // closing this screen
                    finish();
                } else {
                    // failed to create product
                }
            } catch (JSONException e) {
                e.printStackTrace();
            }

            return null;
        }

        /**
         * After completing background task Dismiss the progress dialog
         * **/
        protected void onPostExecute(String file_url) {
            // dismiss the dialog once done
            pDialog.dismiss();
        }

    }

     @Override  
        protected void onStop() {  
         super.onStop();  
         if (pDialog != null) {  
             pDialog.dismiss();  
             pDialog= null;  
         }  
        }  
}

这是我的php文件

<?php
$response = array();

// check for required fields
if (isset($_POST['name']) && isset($_POST['price']) && isset($_POST['description'])) {

    $name = $_POST['name'];
    $price = $_POST['price'];
    $description = $_POST['description'];

    // include db connect class
    require_once __DIR__ . '/db_connect.php';

    // connecting to db
    $db = new DB_CONNECT();

    // mysql inserting a new row
    $result = mysql_query("INSERT INTO products(name, price, description) VALUES('$name', '$price', '$description')");

    // check if row inserted or not
    if ($result) {
        // successfully inserted into database
        $response["success"] = 1;
        $response["message"] = "Product successfully created.";

        // echoing JSON response
        echo json_encode($response);
    } else {
        // failed to insert row
        $response["success"] = 0;
        $response["message"] = "Oops! An error occurred.";

        // echoing JSON response
        echo json_encode($response);
    }
} else {
    // required field is missing
    $response["success"] = 0;
    $response["message"] = "Required field(s) is missing";

    // echoing JSON response
    echo json_encode($response);
}
?>

这是错误。

06-28 00:34:01.849: E/AndroidRuntime(479): FATAL EXCEPTION: AsyncTask #1
06-28 00:34:01.849: E/AndroidRuntime(479): java.lang.RuntimeException: An error occured while executing doInBackground()
06-28 00:34:01.849: E/AndroidRuntime(479):  at android.os.AsyncTask$3.done(AsyncTask.java:200)
06-28 00:34:01.849: E/AndroidRuntime(479):  at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
06-28 00:34:01.849: E/AndroidRuntime(479):  at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
06-28 00:34:01.849: E/AndroidRuntime(479):  at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
06-28 00:34:01.849: E/AndroidRuntime(479):  at java.util.concurrent.FutureTask.run(FutureTask.java:137)
06-28 00:34:01.849: E/AndroidRuntime(479):  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1068)
06-28 00:34:01.849: E/AndroidRuntime(479):  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:561)
06-28 00:34:01.849: E/AndroidRuntime(479):  at java.lang.Thread.run(Thread.java:1096)
06-28 00:34:01.849: E/AndroidRuntime(479): Caused by: java.lang.NullPointerException
06-28 00:34:01.849: E/AndroidRuntime(479):  at com.example.androidhive.NewProductActivity$CreateNewProduct.doInBackground(NewProductActivity.java:102)
06-28 00:34:01.849: E/AndroidRuntime(479):  at com.example.androidhive.NewProductActivity$CreateNewProduct.doInBackground(NewProductActivity.java:1)
06-28 00:34:01.849: E/AndroidRuntime(479):  at android.os.AsyncTask$2.call(AsyncTask.java:185)
06-28 00:34:01.849: E/AndroidRuntime(479):  at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)