NullPointerException for ProgressDialog in AsyncTask

Question

I have an AsyncTask class within another class in a separate file from MainActivity

GetWarehouseSales.java

public class GetWarehouseSales extends Activity {

    private String TAG = MainActivity.class.getSimpleName();
    private ListView lv;
    private ProgressDialog pDialog;
    //URL to get JSON details
    private static String url = "http://192.168.0.1/mycc/retrieve_ws.php";
    ArrayList<HashMap<String,String>> sales_details;

    public GetWarehouseSales(){
    }

    public void executeGWS(){
        new RetrieveWarehouseSalesTask().execute();
    }


    public class RetrieveWarehouseSalesTask extends AsyncTask<Void,Void,Void>{

        public RetrieveWarehouseSalesTask(){

        }

        @Override
        protected void onPreExecute(){
            super.onPreExecute();
            pDialog = new ProgressDialog(GetWarehouseSales.this);
            pDialog.setMessage("Getting you the best warehouse sales...");
            pDialog.setCancelable(false);
            pDialog.show();
        }

        @Override
        protected Void doInBackground(Void... arg0){
            HttpHandler sh = new HttpHandler();
            //making a request to URL and getting response
            String jsonStr = sh.makeServiceCall(url);
            Log.e(TAG, "Response from url: " + jsonStr);

            if(jsonStr != null){
                try{
                    JSONObject jsonObj = new JSONObject(jsonStr);
                    //Getting JSON Array Node
                    JSONArray sales = jsonObj.getJSONArray("Result");
                    //looping through all results
                    for(int i = 0; i<sales.length();i++){
                        JSONObject s = sales.getJSONObject(i);
                        String title = s.getString("title");
                        String description = s.getString("description");

                        HashMap<String,String> salesDetails = new HashMap<>();

                        //adding each child node to HashMap key =>value
                        salesDetails.put("title",title);
                        salesDetails.put("description",description);

                        //adding to array list
                        sales_details.add(salesDetails);
                    }
                    Log.d("TAG",sales_details.toString());
                }catch(final JSONException e){
                    Log.e(TAG, "JSON parsing error: " + e.getMessage());
                    runOnUiThread(new Runnable() {
                        @Override
                        public void run() {
                            Toast.makeText(getApplicationContext(),"JSON parsing error: " + e.getMessage(),Toast.LENGTH_LONG).show();
                        }
                    });
                }
            }else{
                Log.e(TAG,"Couldn't get json from server");
                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        Toast.makeText(getApplicationContext(), "Check logcat", Toast.LENGTH_LONG ).show();
                    }
                });
            }
            return null;
        }

        @Override
        protected void onPostExecute(Void result){
            super.onPostExecute(result);
            if(pDialog.isShowing()){
                pDialog.dismiss();
            }

            //update parsed JSON data into ListView
            ListAdapter adapter = new SimpleAdapter(GetWarehouseSales.this, sales_details,R.layout.item_listview, new String[]{
                    "title","description"}, new int[]{R.id.text,R.id.description});

            lv.setAdapter(adapter);
        }
    }


}

MainActivity.java

 @Override
    protected void onCreate(Bundle savedInstanceState) {
        GetWarehouseSales gws = new GetWarehouseSales();
        gws.executeGWS();

    }

The error:

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.pm.ApplicationInfo android.content.Context.getApplicationInfo()' on a null object reference

The error point to this line:

pDialog = new ProgressDialog(GetWarehouseSales.this);

I would like to execute the AsyncTask RetrieveWarehouseSalesTask which can be found in GetWarehouseSales.java in MainActivity.java but getting NPE errors.

I can't really tell what's the issue with that code, but I think you have to actually start the activity. Otherwise it's not gonna have a context. A stack trace or functional example code would be helpful. — Distjubo, Jan 01 '17 at 11:01

rafsanahmad007 · Accepted Answer · 2017-01-01T11:41:12.687

4

try passing the MainActivity Context..

 @Override
protected void onCreate(Bundle savedInstanceState) {
    GetWarehouseSales gws = new GetWarehouseSales(MainActivity.this);
    gws.executeGWS();

}

Retreive the context:

private Activity activityContext;


 public GetWarehouseSales(Activity context){
     this.activityContext=context;
}

Now initialize your ProgressDialog using that context

 @Override
    protected void onPreExecute(){
        super.onPreExecute();
        pDialog = new ProgressDialog(activityContext);
        pDialog.setMessage("Getting you the best warehouse sales...");
        pDialog.setCancelable(false);
        pDialog.show();
    }

or ..try using

 pDialog = new ProgressDialog(getApplicationContext());

edited Jan 01 '17 at 11:41

answered Jan 01 '17 at 11:05

rafsanahmad007

23,683
6
47
62

Now the error points to pDialog.show(). The error message is "MainActivity has leaked window DecorView@17887f5[] that was originally added here" – kylas Jan 01 '17 at 11:19
@kylas try the edit.... – rafsanahmad007 Jan 01 '17 at 11:30
window leaked exception is caused due to your mainactivity get destroyed while showing the progressdialog – rafsanahmad007 Jan 01 '17 at 11:36

score 0 · Answer 2 · answered Jan 01 '17 at 11:06

This is the reason of the error:

    GetWarehouseSales gws = new GetWarehouseSales();
    gws.executeGWS();

You create an instance of activity, and when the AsyncTask is executing, try to get access to the Context.

Looks like the simpliest fix is to place RetrieveWarehouseSalesTask into MainActivity, something like:

class MainActivity ... {
    ...
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        ...

        new RetrieveWarehouseSalesTask().execute();
    }

    public class RetrieveWarehouseSalesTask extends AsyncTask<Void,Void,Void>{
    ...
}

score 0 · Answer 3 · answered Jan 01 '17 at 12:17

hope this will help you..

@Override
protected void onCreate(Bundle savedInstanceState) {
    GetWarehouseSales gws = new GetWarehouseSales(this);
    gws.executeGWS();

}

Retreive the context:

private Context activityContext;

 public GetWarehouseSales(Context context){
     this.activityContext=context;
}

Now initialize your ProgressDialog using that context

@Override
    protected void onPreExecute(){
        super.onPreExecute();
        pDialog = new ProgressDialog(activityContext);
        pDialog.setMessage("Getting you the best warehouse sales...");
        pDialog.setCancelable(false);
        pDialog.show();
    }

NullPointerException for ProgressDialog in AsyncTask

3 Answers3

Linked