Null pointer Error in Async Task

Question

I am getting a null pointer exception while handling JSON data, i have checked that JSON which i am getting is correct. further i want to store this data in hash map and retrive it one by one as per the requirements.

    public ProgressDialog pDialognew;
static JSONParser jParser = new JSONParser();
ArrayList<HashMap<String, String>> allValueList;

class SearchData extends AsyncTask<String, String, String> {
    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        pDialognew = new ProgressDialog(Activity.this);
        pDialognew.setMessage("Loading. Please wait...");
        pDialognew.setIndeterminate(false);
        pDialognew.setCancelable(true);
        pDialognew.show();
}
@Override
protected String doInBackground(String... params) {
    runOnUiThread(new Runnable() {
        @Override
        public void run() {
            int success;
try 
{
    List<NameValuePair> params = new ArrayList<NameValuePair>();
    params.add(new BasicNameValuePair("match",pName));

    JSONObject json = jParser.makeHttpRequest(GlobalServerLocation.url_pol, "GET", params);
    success = json.getInt("success");
    if (success == 1) 
    {
    JSONArray productObj = json.getJSONArray("object"); // JSON Array
    Log.i("val", productObj.toString());    // Correct JSON
    total = productObj.length();        // Correct number of rows
    Log.i("Len", String.valueOf(total));
    for (int j = 0; j < productObj.length(); j++) 
        {
        JSONObject productnew = productObj.getJSONObject(j);
        String LS = productnew.getString(TAG_LS);
        String CN = productnew.getString(TAG_CN);
        String SN = productnew.getString(TAG_SN);
        String PN = productnew.getString(TAG_PN);

        HashMap<String, String> map = new HashMap<String, String>();
        map.put(TAG_LS, LS);
        map.put(TAG_CN, CN);
        map.put(TAG_SN, SN);
        map.put(TAG_PN, PN);
        allValueList.add(map);
        }
    }
    else
    {
        Log.i("Error", " Some Error from Php Script");
    }
}
catch (JSONException e) 
    {
    Log.i("Error", e.toString());
    }

}
    });
    return null;
}
@Override
protected void onPostExecute(String file_url) {
    pDialognew.dismiss();   // Line 113

    }
}

08-23 17:17:33.449: E/AndroidRuntime(31930): FATAL EXCEPTION: main
08-23 17:17:33.449: E/AndroidRuntime(31930): java.lang.NullPointerException
08-23 17:17:33.449: E/AndroidRuntime(31930):    at my.india.our.app$SearchData$1.run(app.java:113)
08-23 17:17:33.449: E/AndroidRuntime(31930):    at android.os.Handler.handleCallback(Handler.java:587)
08-23 17:17:33.449: E/AndroidRuntime(31930):    at android.os.Handler.dispatchMessage(Handler.java:92)
08-23 17:17:33.449: E/AndroidRuntime(31930):    at android.os.Looper.loop(Looper.java:123)
08-23 17:17:33.449: E/AndroidRuntime(31930):    at android.app.ActivityThread.main(ActivityThread.java:3729)
08-23 17:17:33.449: E/AndroidRuntime(31930):    at java.lang.reflect.Method.invokeNative(Native Method)
08-23 17:17:33.449: E/AndroidRuntime(31930):    at java.lang.reflect.Method.invoke(Method.java:507)
08-23 17:17:33.449: E/AndroidRuntime(31930):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:874)
08-23 17:17:33.449: E/AndroidRuntime(31930):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:632)
08-23 17:17:33.449: E/AndroidRuntime(31930):    at dalvik.system.NativeStart.main(Native Method)

If any other part of Code is required let me know.

seems pDialognew is not an object, is sometihng else accessing/dismissing/destroying it before postexecute executes — Patrick Evans
– Patrick Evans, Commented Aug 23, 2013 at 12:22

Hariharan · Accepted Answer · 2013-08-23 12:37:23Z

1

Normally AsyncTask is used as new thread to perform heavy operations without blocking main UI thread.But, you have used the code which i mentioned below inside doInBackground() of AsyncTask, which will again make the process to be performed in main thread(especially in higher version mobiles), blocking it. so, better remove the following lines and try running it..

runOnUiThread(new Runnable() {
        @Override
        public void run() {

}
};

edited Aug 23, 2013 at 12:37

answered Aug 23, 2013 at 12:21

Hariharan

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Milos Cuculovic · Accepted Answer · 2013-08-23 12:24:03Z

0

An AsyncTask has several parts: a doInBackground method that does, in fact, run on a separate thread, and a onPostExecute method that runs on the UI thread. The purpose of onPostExecute is to publish results (such as updating the view hierarchy, or setting text in a text view) that must be done on the UI thread. It also can post progress updates. In order for this to all work properly, the AsyncTask must be created, and the execute method called, on the UI thread.

You must not call UI actions from within doInBackground -- doing so will crash your application.

answered Aug 23, 2013 at 12:24

Milos Cuculovic

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1 Comment

user2327124 Over a year ago

I am grateful for your response, but if can also point out my mistake in the code above i will be grateful. what i have done is just to get data and put in a hashmap, and i have been doing the same for quite a long time.

Ridcully · Accepted Answer · 2013-08-23 12:41:37Z

0

First of all, move the declaration of pDialognew into your SearchData class.

Second, as Hari pointed out, get rid off the runOnUiThread stuff. Your doInBackground() method should look about like so:

protected String doInBackground(String... params) {
    try {
        List<NameValuePair> params = new ArrayList<NameValuePair>();
        // ... rest of your code
    } catch (JSONException e) {
        Log.i("Error", e.toString());
    }
    return null;
}

Third, in your onPostExecute() method, ensure, pDialognew is not null (altough I have no idea how it can be null here):

if (pDialognew != null) pDialognew.dismiss();

answered Aug 23, 2013 at 12:41

Ridcully

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