android - App keeps stopping when i press a button -

i have save button loads dialog interface asking save name. when click done it's supposed created sharedpreferences strings in it, instead says unfortunately program has stopped. how can fix this? oh , want put out there i'm new android. i'm learning of stuff make app.

public void save(view view){      layoutinflater li = layoutinflater.from(calculate.this);     view pview = li.inflate(r.layout.prompt, null);      alertdialog.builder adb = new alertdialog.builder(calculate.this);     adb.setview(pview);      final edittext name = (edittext) findviewbyid(r.id.etprompt);      adb.setcancelable(false);     adb.setpositivebutton("done", new dialoginterface.onclicklistener() {          @override         public void onclick(dialoginterface dialog, int which) {             n = name.gettext().tostring();             try {                 details = getsharedpreferences(n,mode_private);                 editor = details.edit();                 editor.putstring("ebp", ebp.gettext().tostring());                 editor.putstring("fb", fb.gettext().tostring());                 editor.putstring("sv", sv.gettext().tostring());                 editor.putstring("pv", pv.gettext().tostring());                 editor.putstring("sl", sl.gettext().tostring());                 editor.putstring("cl", cl.gettext().tostring());                 editor.commit();             } catch (exception e) {                 // todo auto-generated catch block                 e.printstacktrace();             }         }     });      adb.setnegativebutton("cancel", new dialoginterface.onclicklistener() {          @override         public void onclick(dialoginterface dialog, int which) {             dialog.cancel();          }     });      alertdialog ad = adb.create();     ad.show();   } 

logcat

05-18 20:54:28.300: e/androidruntime(16575): fatal exception: main  05-18 20:54:28.300: e/androidruntime(16575): java.lang.nullpointerexception  05-18 20:54:28.300: e/androidruntime(16575):    @                   com.tbjsoft.enclosurecalculator.calculate$1.onclick(calculate.java:103)  05-18 20:54:28.300: e/androidruntime(16575):    @ com.android.internal.app.alertcontroller$buttonhandler.handlemessage(alertcontroller.java:166)  05-18 20:54:28.300: e/androidruntime(16575):    @ android.os.handler.dispatchmessage(handler.java:99)  05-18 20:54:28.300: e/androidruntime(16575):    @ android.os.looper.loop(looper.java:137)  05-18 20:54:28.300: e/androidruntime(16575):    @ android.app.activitythread.main(activitythread.java:5041)  05-18 20:54:28.300: e/androidruntime(16575):    @ java.lang.reflect.method.invokenative(native method)  05-18 20:54:28.300: e/androidruntime(16575):    @ java.lang.reflect.method.invoke(method.java:511)  05-18 20:54:28.300: e/androidruntime(16575):    @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:793)  05-18 20:54:28.300: e/androidruntime(16575):    @ com.android.internal.os.zygoteinit.main(zygoteinit.java:560)  05-18 20:54:28.300: e/androidruntime(16575):    @ dalvik.system.nativestart.main(native method) 

you need use activities context access sharedpreferences inside alertdialog. can either initialize them outside of alertdialog or change to

   details =  caluclate.this.getsharedpreferences(n,mode_private);  // assuming calculate name of `activity` 

if doesn't please post logcat know crashing

edit

change

final edittext name = (edittext) findviewbyid(r.id.etprompt); 

to

final edittext name = (edittext) pview.findviewbyid(r.id.etprompt);