android - NullPointerException: Attempt to invoke virtual method AlertDialog.setTitle(java.lang.CharSequence) on a null object reference -

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• what nullpointerexception, , how fix it? 12 answers

here error:

04-01 10:37:47.077 2310-2326/zonup.asyc d/create response﹕ {"success":"false","msg":"please enter email!!!"} 04-01 10:37:47.084
2310-2310/zonup.asyc d/androidruntime﹕ shutting down vm 04-01 10:37:47.084 2310-2310/zonup.asyc e/androidruntime﹕ fatal exception: main process: zonup.asyc, pid: 2310 java.lang.nullpointerexception: attempt invoke virtual method 'void android.app.alertdialog.settitle(java.lang.charsequence)' on null object reference @ zonup.asyc.mainactivity$signmeup.onpostexecute(mainactivity.java:122) @ zonup.asyc.mainactivity$signmeup.onpostexecute(mainactivity.java:70) @ android.os.asynctask.finish(asynctask.java:632) @ android.os.asynctask.access$600(asynctask.java:177) @ android.os.asynctask$internalhandler.handlemessage(asynctask.java:645) @ android.os.handler.dispatchmessage(handler.java:102) @ android.os.looper.loop(looper.java:135) @ android.app.activitythread.main(activitythread.java:5221) @ java.lang.reflect.method.invoke(native method) @ java.lang.reflect.method.invoke(method.java:372) @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:899) @ com.android.internal.os.zygoteinit.main(zygoteinit.java:694)

public class mainactivity extends actionbaractivity {  protected string stmail; protected edittext edittext; protected button button; alertdialog alertdialog;  @override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.activity_main);     edittext=(edittext) findviewbyid(r.id.edittext);     stmail=edittext.gettext().tostring();     button=(button) findviewbyid(r.id.button);     button.setonclicklistener(new view.onclicklistener() {         @override         public void onclick(view v) {             new signmeup().execute();         }     }); }   @override public boolean oncreateoptionsmenu(menu menu) {     // inflate menu; adds items action bar if present.     getmenuinflater().inflate(r.menu.menu_main, menu);     return true; }  @override public boolean onoptionsitemselected(menuitem item) {     // handle action bar item clicks here. action bar     // automatically handle clicks on home/up button, long     // specify parent activity in androidmanifest.xml.     int id = item.getitemid();      //noinspection simplifiableifstatement     if (id == r.id.action_settings) {         return true;     }      return super.onoptionsitemselected(item); } class signmeup extends asynctask<string, string, string> {      private progressdialog pdialog;     jsonparser jsonparser = new jsonparser();      @override     protected void onpreexecute() {         super.onpreexecute();         runonuithread(new runnable() {             @override             public void run() {                 pdialog = new progressdialog(mainactivity.this);                 pdialog.setmessage("thanks sign up...");                 pdialog.setindeterminate(false);                 pdialog.setcancelable(true);             }         });     }      @override     protected string doinbackground(string... arg0) {         // todo auto-generated method stub          // building parameters         list<namevaluepair> params = new arraylist<namevaluepair>();         params.add(new basicnamevaluepair("email", stmail));            // getting json object         // note create product url accepts post method         jsonobject json = jsonparser.makehttprequest("http://api.php","get", params);          // check log cat fro response         log.d("create response", json.tostring());          // check success tag         try {             string success = json.getstring("success");              if (stmail != null & success == "true") {                 toast.maketext(mainactivity.this, "youre email posted..", toast.length_short).show();             } else {              }         } catch (jsonexception e) {             e.printstacktrace();         }          return null;     }      @suppresswarnings("deprecation")     protected void onpostexecute(string file_url) {         // dismiss dialog once done          edittext.settext("");         alertdialog.settitle("info");          alertdialog.setmessage("you have been subscribed o ");         alertdialog.setbutton("ok", new dialoginterface.onclicklistener() {             public void onclick(dialoginterface dialog, int which) {                 // here can add functions              }         });          alertdialog.show();      }  } } 

rather using alertdialog use alertdialog.builder. alertdialog deprected. need show progressdialog too.

 @override     protected void onpreexecute() {         super.onpreexecute();         pdialog = new progressdialog(mainactivity.this);         pdialog.setmessage("thanks sign up...");         pdialog.setindeterminate(false);         pdialog.setcancelable(true);         pdialog.show();     } 

in onpostexecute method dismiss progressbar. use alertdialog.builder.

 protected void onpostexecute(string file_url) {         // dismiss dialog once done       if(pdialog.isshowing()){        pdialog.dismiss();       }         edittext.settext("");       alertdailog.builder builder = new alertdialog.builder(activity.this);              builder.settext("");              builder.setmessege("");              builder.create().show();         });