android - Change TextView value on Activity creation -

i want change textviews value when activity created.

on loginactivity, start activity using:

startactivity(new intent(loginactivity.this, mainactivity.class)); 

but dont know place code changing textviews value.

when place in oncreate, app crashes...

my logcat not working cant see exceptions...

but crashes when doing

    textview t = (textview) findviewbyid(r.id.zanuka_username);     t.settext("lllll"); 

oncreate

 @override     protected void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         setcontentview(r.layout.activity_main);          textview t = (textview) findviewbyid(r.id.zanuka_username);         t.settext("lllll");          toolbar toolbar = (toolbar) findviewbyid(r.id.toolbar);         setsupportactionbar(toolbar);         /** floatingactionbutton fab = (floatingactionbutton) findviewbyid(r.id.fab);         fab.setonclicklistener(new view.onclicklistener() {             @override             public void onclick(view view) {                 snackbar.make(view, "replace own action", snackbar.length_long)                         .setaction("action", null).show();             }         });         **/          //imageview profilepicture = (imageview)findviewbyid(r.id.zanuka_profilepicture);         //new imageloadtask("http://chat.keecode.net/account/picture/1", profilepicture).execute();          drawerlayout drawer = (drawerlayout) findviewbyid(r.id.drawer_layout);         actionbardrawertoggle toggle = new actionbardrawertoggle(                 this, drawer, toolbar, r.string.navigation_drawer_open, r.string.navigation_drawer_close);         drawer.setdrawerlistener(toggle);         toggle.syncstate();          navigationview navigationview = (navigationview) findviewbyid(r.id.nav_view);         navigationview.setnavigationitemselectedlistener(this);     } 

you're getting exception:

java.lang.nullpointerexception: attempt invoke virtual method 'void android.widget.textview.settext(java.lang.charsequence)' on null object reference 

which tells textview t null. reason of missing textview id="zanuka_username" in activity_main.xml.