keep getting null pointer exception in asynctasking

Question

Ok so I know I should use interfaces to retrieve information from AsyncTask because they run in separate threads but I have been trying in vain to get this right. Can someone guide me to what is wrong with my code?

First I thought I was getting null pointer exception at callback.onJsonReady(movie) because I was still trying to reach movie that was not processed despite my attempt. So I tried sleeping it for 5000ms before it retrieves but I still get a null pointer exception. please help me.

If you need to look at more of my code, please tell me also.

Below is the method where I set up my interface

        protected void onPostExecute(String s) {
        super.onPostExecute(s);
        processData(getmData());
    }

    private void processData (String mData){
        try {
            final String MOVIE_TITLE = "Title";

            JSONObject jsonObject = new JSONObject(mData);

            Log.v(LOG_TAG, mData);

            String title = jsonObject.getString(MOVIE_TITLE);

            Movie movie = new Movie(title);
            callback.onJsonReady(movie);
            Log.v(LOG_TAG, "Title of the movie is " + movie.getTitle());
        }catch (JSONException e){
            Log.e(LOG_TAG, "Error retrieving JsonData");
            e.printStackTrace();
        }
    }
}

Below is my class where I call the interface

public class ResultsPage extends AppCompatActivity implements ParseJsonData.ParseJsonCallback{

private final String LOG_TAG = getClass().getSimpleName();
private TextView title;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_results_page);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    setTextViews();

}

private void setTextViews () {
    Bundle bundle = getIntent().getExtras();

    String movieTitle = bundle.getString("title");

    Log.v(LOG_TAG, "title recieved is : " + movieTitle);

    ParseJsonData parseJsonData = new ParseJsonData(movieTitle, this);
    parseJsonData.execute();

}

@Override
public void onJsonReady(Movie movie) {
    title.setText(movie.getTitle());
}
}

My logcat is

03-14 18:03:02.931 30827-30827/? E/AndroidRuntime: FATAL EXCEPTION: main
   Process: com.jc.tagyourmovie, PID: 30827
   java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
       at com.jc.tagyourmovie.ResultsPage.onJsonReady(ResultsPage.java:44)
       at com.jc.tagyourmovie.ParseJsonData$ParseJsonDataBackground.processData(ParseJsonData.java:83)
       at com.jc.tagyourmovie.ParseJsonData$ParseJsonDataBackground.onPostExecute(ParseJsonData.java:69)
       at com.jc.tagyourmovie.ParseJsonData$ParseJsonDataBackground.onPostExecute(ParseJsonData.java:53)
       at android.os.AsyncTask.finish(AsyncTask.java:651)
       at android.os.AsyncTask.access$500(AsyncTask.java:180)
       at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:668)
       at android.os.Handler.dispatchMessage(Handler.java:102)
       at android.os.Looper.loop(Looper.java:158)
       at android.app.ActivityThread.main(ActivityThread.java:7224)
       at java.lang.reflect.Method.invoke(Native Method)
       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)

and I set reference of interface to be the one passed into the constructor of the class where I set up the interface — Jchoi, Mar 14 '16 at 18:09
and they are pointing to `callback.onJsonReady(movie)` and movie being null — Jchoi, Mar 14 '16 at 18:12
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) — Henry, Mar 14 '16 at 18:13

score 2 · Answer 1 · answered Mar 14 '16 at 18:14

2

Your Textview title is not initialized... that is the reason

you need to do something like:

title = (TextView)findViewById(R.id.<your_tv_id>);

answered Mar 14 '16 at 18:14

ΦXocę 웃 Пepeúpa ツ

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AAnkit · Accepted Answer · 2016-03-14T18:18:29.187

1

Error is in title.setText line. Logcat says so > java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference

Seems you haven't initialize your textview named title, initialize it before using it.

Your code declared a textview named title

private TextView title;

you have to initialize this textview in onCreate() like below

title = (TextView)findViewById(R.id.TEXTVIEWID);

edited Mar 14 '16 at 18:18

answered Mar 14 '16 at 18:12

AAnkit

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omg... thanks... being a newbie, I still dnt even believe I made such a mistake – Jchoi Mar 14 '16 at 18:16
being a newbie, it is expected. :), everybody does that. No problem there. Keep coding. – AAnkit Mar 14 '16 at 18:17

score 0 · Answer 3 · answered Mar 14 '16 at 18:13

You need to move code that changes UI to the onPostExecute part of the AsyncTask.

callback.onJsonReady(movie);

This part can be in the doInBackground, but use a field of the AsynchTask rather than a local var so you can access it in the onPostExecute:

Movie movie = new Movie(title);

score 0 · Answer 4 · answered Mar 14 '16 at 18:15

0

private TextView title;

You need to give a value to title, something like this:

title = (TextView) R.findViewById(R.id.textviewid);

And after that you can call setText() on it. Replace textviewid with your textview's id in xml file.

answered Mar 14 '16 at 18:15

Vucko

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keep getting null pointer exception in asynctasking

4 Answers4