java - NullPointerException when dialog positive button onClick calls interface -

i'm trying use interface send click event alertdialog.builder.setpositivebutton's onclick event.

please me out. i've been looking on similar problem use guidance.

the npe @ line:

     mlistener.onsetbalancedialogpositiveclick(setbalancedialog.this); 

here logcat:

08-19 20:05:50.469: e/androidruntime(5795): fatal exception: main 08-19 20:05:50.469: e/androidruntime(5795): java.lang.nullpointerexception 08-19 20:05:50.469: e/androidruntime(5795):     @ com.smb.allowance.setbalancedialog$2.onclick(setbalancedialog.java:75) 08-19 20:05:50.469: e/androidruntime(5795):     @ com.android.internal.app.alertcontroller$buttonhandler.handlemessage(alertcontroller.java:159) 08-19 20:05:50.469: e/androidruntime(5795):     @ android.os.handler.dispatchmessage(handler.java:99) 08-19 20:05:50.469: e/androidruntime(5795):     @ android.os.looper.loop(looper.java:123) 08-19 20:05:50.469: e/androidruntime(5795):     @ android.app.activitythread.main(activitythread.java:3683) 08-19 20:05:50.469: e/androidruntime(5795):     @ java.lang.reflect.method.invokenative(native method) 08-19 20:05:50.469: e/androidruntime(5795):     @ java.lang.reflect.method.invoke(method.java:507) 08-19 20:05:50.469: e/androidruntime(5795):     @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:864) 08-19 20:05:50.469: e/androidruntime(5795):     @ com.android.internal.os.zygoteinit.main(zygoteinit.java:622) 08-19 20:05:50.469: e/androidruntime(5795):     @ dalvik.system.nativestart.main(native method) 

here dialog code:

package com.smb.allowance;  import java.text.decimalformat;  import android.app.activity; import android.app.alertdialog; import android.app.dialog; import android.content.context; import android.content.dialoginterface; import android.os.bundle; import android.support.v4.app.dialogfragment; import android.util.log; import android.view.keyevent; import android.view.view; import android.view.inputmethod.editorinfo; import android.view.inputmethod.inputmethodmanager; import android.widget.edittext; import android.widget.textview; import android.widget.textview.oneditoractionlistener; import android.widget.toast;  public class setbalancedialog extends dialogfragment implements oneditoractionlistener {      private edittext edittextsetbalance;     private static double dinput = 0;      public interface setbalancedialoglistener{         public void onsetbalancedialogpositiveclick(dialogfragment dialog);     } // end interface      setbalancedialoglistener mlistener;      public void onattache(activity activity){         super.onattach(activity);          try {             mlistener = (setbalancedialoglistener) activity;         }catch (classcastexception e) {             throw new classcastexception(activity.tostring()                         + " must implement setbalancedialoglistener");             }     } // end onattach      public setbalancedialog(){         // default empty constructor     }// end constructor      public dialog oncreatedialog(bundle savedinstancestate){          view view = getactivity().getlayoutinflater().inflate(r.layout.dialog_balance_set, null);                 edittextsetbalance = (edittext)view.findviewbyid(r.id.edittextsetbalance);          edittextsetbalance.setonclicklistener(new view.onclicklistener() {                   @override             public void onclick(view v) {                     if (!edittextisempty(edittextsetbalance)){                         edittextsetbalance.settext("");                     }                      clearedittext(edittextsetbalance);             }         });          alertdialog.builder builder = new alertdialog.builder(getactivity());         builder.setview(view)         .setcancelable(false)         .setmessage(r.string.set_begin_balance)         .setcancelable(false)         .setpositivebutton(r.string.save, new dialoginterface.onclicklistener() {              @override             public void onclick(dialoginterface dialog, int which) {                 // todo auto-generated method stub                 mlistener.onsetbalancedialogpositiveclick(setbalancedialog.this);             }         });          // show soft keyboard automatically          edittextsetbalance.requestfocus();         edittextsetbalance.setoneditoractionlistener(this);          return builder.create();      } // end oncreatedialog 

the activity implements interface:

package com.smb.allowance;  import java.text.decimalformat;  import android.content.context; import android.content.intent; import android.os.bundle; import android.support.v4.app.dialogfragment; import android.support.v4.app.fragmentactivity; import android.util.log; import android.view.keyevent; import android.view.menu; import android.view.view; import android.view.inputmethod.editorinfo; import android.view.inputmethod.inputmethodmanager; import android.widget.button; import android.widget.edittext; import android.widget.spinner; import android.widget.textview; import android.widget.textview.oneditoractionlistener; import android.widget.toast;  import com.smb.allowance.resetbalancedialogfragment.resetbalancedialoglistener;  public class mainactivity extends fragmentactivity                  implements resetbalancedialoglistener,        setbalancedialog.setbalancedialoglistener {  @override public void onsetbalancedialogpositiveclick(dialogfragment dialog) {     // testing functionality       onreset(); } 

is possible how handling/mishandling edittext view causing npe?

i'm new android/java , programming in general, help.

mlistener null

it null because never assign anything! (oh yes hear think!) don't

you have public voidonattache(activity activity)` method never called because should be

public void onattach(activity activity) 

you should add @override inherited methods , call super. make sure compilation error if method declaration wrong ensuring code in base class inherited method gets run. if method empty in version of sdk using doesn't mean won't empty @ unkown point in future.