java - JSON: Null pointer exception -

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from this tutorial, got error

java.lang.nullpointerexception: attempt invoke virtual method 'java.lang.string org.json.jsonobject.tostring()' on null object reference

it came mainactivity.java

class attemptlogin extends asynctask<string, string, string> { // <--- cause of error     /**      * before starting background thread show progress dialog      * */      boolean failure = false;      @override     protected void onpreexecute() {         super.onpreexecute();         pdialog = new progressdialog(mainactivity.this);         pdialog.setmessage("attempting login...");         pdialog.setindeterminate(false);         pdialog.setcancelable(true);         pdialog.show(); }      @override     protected string doinbackground(string... args) {     // todo auto-generated method stub     // here check success tag     int success;         string username = user.gettext().tostring();         string password = pass.gettext().tostring();         try {             list<namevaluepair> params = new arraylist<namevaluepair>();             params.add(new basicnamevaluepair("username", username));             params.add(new basicnamevaluepair("password", password));              log.d("request!", "starting");              jsonobject json = jsonparser.makehttprequest( login_url, "post", params);              // checking log json response             log.d("login attempt", json.tostring()); // <--- cause of error              // success tag json             success = json.getint(tag_success);             if (success == 1) {                 log.d("successfully login!", json.tostring());                 intent ii = new intent(mainactivity.this,otheractivity.class);                 startactivity(ii);                  // finish() method used tell android os done current                 // activity now! moving other activity                  finish();                 return json.getstring(tag_message);             }              else{                 return json.getstring(tag_message);             }         }         catch (jsonexception e) {             e.printstacktrace();         }          return null;     }      /**      * once background process done need dismiss progress dialog asap      **/      protected void onpostexecute(string message) {         pdialog.dismiss();         if (message != null){             toast.maketext(mainactivity.this, message, toast.length_long).show();         }     } }

there's lots of people asking same question still no answer particular problem.

this first time using json, there's wrong in code , didn't found yet.

hope me figure out did wrong. thank you.

why not favor , use retrofit getting / parsing json.

here tutorials:

http://inthecheesefactory.com/blog/retrofit-2.0/en

https://github.com/codepath/android_guides/wiki/consuming-apis-with-retrofit

http://www.vogella.com/tutorials/retrofit/article.html


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