OnPostExecute result null

Question

I'm sending some data from my app to an external server.

public class PostKey extends AsyncTask<String, String, String> {
    public AsyncResponse delegate = null;

    @Override
    protected String doInBackground(String... params) {
        postData(params[0]);
        return null;
    }

    @Override
    protected void onPostExecute(String result){
        Log.d(String.valueOf(result), " Result?");
        delegate.processFinish(result); // Returns NullPointerException
    }

    public void postData(String valueIWantToSend) {
        HttpClient httpclient = new DefaultHttpClient();
        HttpPost httppost     = new HttpPost("http://domain.com/post.php");

        try {
            List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();
            nameValuePairs.add(new BasicNameValuePair("hoi", "test"));
            httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));

            HttpResponse response = httpclient.execute(httppost);
            String responseStr = EntityUtils.toString(response.getEntity());

            Log.d(responseStr, "");
        } catch (ClientProtocolException e) {
            // TODO Auto-generated catch block
        } catch (IOException e) {
            // TODO Auto-generated catch block
        }
    }

    public interface AsyncResponse {
        void processFinish(String output);
    }
}

Log.d(responseStr, ""); does return true or false, depending on what data was send, and logs it.

delegate.processFinish(result); returns the NullPointerException also mentioning public class PostKey extends AsyncTask<String, String, String> eventhough all the parameters are declared as Strings.

I've also tried replacing result with responseStr but that didn't work either.

You return null from doInBackground method so you get null in onPostExecute — SANAT, Jul 17 '15 at 11:52
You can pass the same to the constructor of asynctask and do `delegate= (AsyncResponse) activity;` Note : Activity implements the interface. — Raghunandan, Jul 17 '15 at 11:53
`void postData` => `String postData`, `Log.d(responseStr, "");` => `return responseStr` (also add `return null;` at the end of this method), body of `doInBackground` => `return postData(params[0]);` ... add null check in `onPostExecute` ... still `delegate` can be null if you do not set it ... — Selvin, Jul 17 '15 at 11:55
... but still ... possible duplicate of [What is a Null Pointer Exception, and how do I fix it?](http://stackoverflow.com/questions/218384/what-is-a-null-pointer-exception-and-how-do-i-fix-it) — Selvin, Jul 17 '15 at 11:56
@sanatshukla there has to be a retun statement there, otherwise an error displays. With what could I replace it? Just `return;` isn't valid either — Orynuh, Jul 17 '15 at 11:57
onPostExecute get the data return by doInBackground method. So, if you return it a null then you get null in onPostExecute. — SANAT, Jul 17 '15 at 11:58

score 1 · Answer 1 · answered Jul 17 '15 at 11:56

1

Problem with your method call delegate.processFinish(result); delegate is not initialized. So you are calling a method on null object.

answered Jul 17 '15 at 11:56

Raghu Mudem

6,793
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gmetax · Answer 2 · 2015-07-17T12:00:39.227

change your code to that

public class PostKey extends AsyncTask<String, String, String> {
    public AsyncResponse delegate = null;

    public PostKey(AsyncResponse asyncResponse) {
        delegate = asyncResponse;
    }   

    @Override 
    protected String doInBackground(String... params) {
        return postData(params[0]);
    } 

    @Override 
    protected void onPostExecute(String result){
        Log.d(String.valueOf(result), " Result?");
        delegate.processFinish(result);
    } 

    public String postData(String valueIWantToSend) {
        HttpClient httpclient = new DefaultHttpClient();
        HttpPost httppost     = new HttpPost("http://domain.com/post.php");

        try { 
            List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();
            nameValuePairs.add(new BasicNameValuePair("hoi", "test"));
            httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));

            HttpResponse response = httpclient.execute(httppost);
            String responseStr = EntityUtils.toString(response.getEntity());

            Log.d(responseStr, "");
        } catch (ClientProtocolException e) {
            // TODO Auto-generated catch block 
        } catch (IOException e) {
            // TODO Auto-generated catch block 
        } 
        return responseStr;
    } 

    public interface AsyncResponse { 
        void processFinish(String output);
    } 
}

score 0 · Answer 3 · answered Jul 17 '15 at 12:03

If you want the result of postData() then change the return type of postData() from void to String and return that result to onPostExecute like this :

public class PostKey extends AsyncTask<String, String, String> {
    public AsyncResponse delegate = null;

    @Override
    protected String doInBackground(String... params) {
        return postData(params[0]);
    }

    @Override
    protected void onPostExecute(String result){
        Log.d(String.valueOf(result), " Result?");
        delegate.processFinish(result); // Returns NullPointerException
    }

    public String postData(String valueIWantToSend) {
        HttpClient httpclient = new DefaultHttpClient();
        HttpPost httppost     = new HttpPost("http://domain.com/post.php");

        try {
            List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();
            nameValuePairs.add(new BasicNameValuePair("hoi", "test"));
            httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));

            HttpResponse response = httpclient.execute(httppost);
            String responseStr = EntityUtils.toString(response.getEntity());
            return responseStr;
            Log.d(responseStr, "");
        } catch (ClientProtocolException e) {
            // TODO Auto-generated catch block
        } catch (IOException e) {
            // TODO Auto-generated catch block
        }
       return null;
    }

    public interface AsyncResponse {
        void processFinish(String output);
    }
}

OnPostExecute result null

3 Answers3