android.os.NetworkOnMainThreadException错误，即使在AsyncTask中运行

Question

i am getting the android.os.NetworkOnMainThreadException error when i try to connect to the internet.I know that the later versions of android(HoneyComb onwards) do not allow you to perform network IO on the UI thread that's why i am using the AsyncTask.no errors on the code but when it runs,i get the android.os.NetworkOnMainThreadException error the code:

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.mainactivity);
    new GetProductDetails().execute();
}

class GetProductDetails 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 product details. Please wait...");
        pDialog.setIndeterminate(false);
        pDialog.setCancelable(true);
        pDialog.show();
    }

    /**
     * Getting product details in background thread
     * */
    protected String doInBackground(String... params) {

        // updating UI from Background Thread
        runOnUiThread(new Runnable() {
            public void run() {
                // Check for success tag
                int success;
                try {
                    // Building Parameters
                    List<NameValuePair> params = new ArrayList<NameValuePair>();
                    params.add(new BasicNameValuePair("pid", pid));

                    // getting product details by making HTTP request
                    // Note that product details url will use GET request
                    JSONObject json = jsonParser.makeHttpRequest(
                            url_product_details, "GET", params);

                    // check your log for json response
                    Log.d("Single Product Details", json.toString());

                    // json success tag
                    success = json.getInt(TAG_SUCCESS);
                    if (success == 1) {
                        // successfully received product details
                        JSONArray productObj = json
                                .getJSONArray(TAG_PRODUCT); // JSON Array

                        // get first product object from JSON Array
                        JSONObject product = productObj.getJSONObject(0);


                        txtName = (EditText) findViewById(R.id.inputName);
                        txtPrice = (EditText) findViewById(R.id.inputPrice);
                        txtDesc = (EditText) findViewById(R.id.inputDesc);

                        // display product data in EditText
                        txtName.setText(product.getString(TAG_NAME));
                        txtPrice.setText(product.getString(TAG_PRICE));
                        txtDesc.setText(product.getString(TAG_DESCRIPTION));


                    }else{
                        // product with pid not found
                    }
                } 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 got all details
        pDialog.dismiss();
    }
}

i have read that a possible solution to this is using the StrictMode Policy but i am a bit reluctant to use this because it is recommended in development environments only.what's the problem here?

Answer 1

What's the problem here?

You are doing network I/O on the main application thread, from inside the Runnable you are using with runOnUiThread() .

Get rid of the runOnUiThread() and Runnable . Put the networking code in doInBackground() . Update your widgets in onPostExecute() . You pass data from doInBackground() to onPostExecute() either by the return value from doInBackground() (which becomes the parameter passed to onPostExecute() ) or data members inside of the AsyncTask itself.

Answer 2

You are using AsyncTask but in doInBackground you are calling

// updating UI from Background Thread
        runOnUiThread(new Runnable() {
            public void run() {

In these strings you run all next code from doInBackground in main UI thread and it removes all AsyncTask effect.

Than you run

JSONObject json = jsonParser.makeHttpRequest(
                            url_product_details, "GET", params);

and it runs in main thread, as I described below. So, it throws the exception.

Move all your network code out of Runnable and put your Runnable at the end of doInBackground with only updates of widgets - it should works.

Answer 3

You are running network related operation on the ui thread.

You are using runOnUiThread inside doInbackground() . Inside runOnUiThread you have the below

JSONObject json = jsonParser.makeHttpRequest(
                        url_product_details, "GET", params);

This causes NetworkOnMainThreadException .

You are also missing @Override Annotation for doInBackground() and onPostExecute() .

A can make the json request in doInbackground() and update ui in onPostExecute() .

If you use runOnUiThread use it to update ui and move all network related operation in doInbackground .

You can also move the below to onCreate .

  txtName = (EditText) findViewById(R.id.inputName);
  txtPrice = (EditText) findViewById(R.id.inputPrice);
  txtDesc = (EditText) findViewById(R.id.inputDesc);

Return the result of background computation in doInbackground . The result of doInbackground is a parameter to onPostExecute. You can use the same to update ui in onPostExecute .

For more info check the docs

http://developer.android.com/reference/android/os/AsyncTask.html