android - How to use SharedPreferences to store int that is incremented everytime the user clicks a button & retrieve value next time the app is launched -

im beginner android dev, , ive been working on pretty straightforward voting app school.

basically i've created objects in multiple activities act int counters record votes(in form of clicks) various posts. have achieved , able view results counters in different activity. also, activity shifts new activity next position in voting system automatically.

i realised lose data/votes objects(counters) if app killed or crashed. therefore, tried implementing shared preferences store , update count of votes when button clicked.

however, app crashes when use code reassign shared preference variable counter objects value.

i cannot seem understand , fix code counter resumes last value. below code:

public class spl extends appcompatactivity {  sharedpreferences retrieve = getapplicationcontext().getsharedpreferences("result", mode_private);  public int spl1count = retrieve.getint("hb1", 0); public int spl2count = retrieve.getint("hb2", 0);  @override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.activity_spl);      final button spl1vb = (button) findviewbyid(r.id.spl1vb);     final button spl2vb = (button) findviewbyid(r.id.spl2vb);       spl1vb.setonclicklistener(new view.onclicklistener() {         @override         public void onclick(view v) {             spl1count ++;             sharedpreferences sharedpref = getsharedpreferences("result", context.mode_private);              sharedpreferences.editor editor = sharedpref.edit();              editor.putint("hb1", spl1count);             editor.apply();             toast.maketext(getapplicationcontext(),"saved ", toast.length_short).show();              intent intent = new intent(getapplicationcontext(), aspl.class);             intent.setflags(intent.flag_activity_clear_top);             startactivity(intent);             finish();         }     });       spl2vb.setonclicklistener(new view.onclicklistener() {         @override         public void onclick(view v) {             spl2count ++;             sharedpreferences sharedpref = getsharedpreferences("result", context.mode_private);              sharedpreferences.editor editor = sharedpref.edit();              editor.putint("hb2", spl2count);             editor.apply();             toast.maketext(getapplicationcontext(),"saved ", toast.length_short).show();              intent intent = new intent(getapplicationcontext(), aspl.class);             intent.setflags(intent.flag_activity_clear_top);             startactivity(intent);             finish();         }     });   } 

the app crashes , after looking @ log tells me there error on line used shared preference 'retrieved' old data fit counter.

if remove this, counter sets 0 when launched again, believe because counter isn't being set shared preference value.

here code collecting results shared preference in activity:

  sharedpreferences sharedpref = getsharedpreferences("result", context.mode_private);      final int spl1r = sharedpref.getint("hb1", 0);     final int spl2r = sharedpref.getint("hb2", 0); 

then use alert dialog box display spl1r , spl2r.

i've spent hours on internet searching solution none have worked me. appreciated. in advance

---

so updated code based on evin's answer, code still crashes, time in oncreate

here new code:

     public class spl extends appcompatactivity {   sharedpreferences retrieve; public int spl1count; public int spl2count;  @override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.activity_main);      retrieve = getapplicationcontext().getsharedpreferences("result", mode_private);     spl1count = retrieve.getint("hb1", 0);     spl2count = retrieve.getint("hb2", 0);       button spl1vb = (button) findviewbyid(r.id.spl1vb);      button spl2vb = (button) findviewbyid(r.id.spl2vb);        spl1vb.setonclicklistener(new view.onclicklistener() {         @override         public void onclick(view v) {             spl1count ++;             sharedpreferences sharedpref = getsharedpreferences("result", context.mode_private);              sharedpreferences.editor editor = sharedpref.edit();              editor.putint("hb1", spl1count);             editor.apply();             toast.maketext(getapplicationcontext(),"saved ", toast.length_short).show();              intent intent = new intent(getapplicationcontext(), aspl.class);             intent.setflags(intent.flag_activity_clear_top);             startactivity(intent);             finish();         }     });       spl2vb.setonclicklistener(new view.onclicklistener() {         @override         public void onclick(view v) {             spl2count ++;             sharedpreferences sharedpref = getsharedpreferences("result", context.mode_private);              sharedpreferences.editor editor = sharedpref.edit();              editor.putint("hb2", spl2count);             editor.apply();             toast.maketext(getapplicationcontext(),"saved ", toast.length_short).show();              intent intent = new intent(getapplicationcontext(), aspl.class);             intent.setflags(intent.flag_activity_clear_top);             startactivity(intent);             finish();         }     });   } 

am still doing wrong? thank you.

put these lines inside oncreate:

sharedpreferences retrieve = getapplicationcontext().getsharedpreferences("result", mode_private);  public int spl1count = retrieve.getint("hb1", 0); public int spl2count = retrieve.getint("hb2", 0); 

you initializing them when have no reference android context yet (which built in oncreate method of activity/application) that's why getsharedpreferences method of applicationcontext null reference.

---

if still want declare these values member variables, class (splitting declaration , assignment):

public class spl extends appcompatactivity {     sharedpreferences retrieve;     public int spl1count;     public int spl2count;      @override     protected void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         setcontentview(r.layout.activity_spl);          retrieve = getapplicationcontext().getsharedpreferences("result", mode_private);         spl1count = retrieve.getint("hb1", 0);         spl2count = retrieve.getint("hb2", 0);          final button spl1vb = (button) findviewbyid(r.id.btn1);         final button spl2vb = (button) findviewbyid(r.id.btn2);         /* listeners */     } }