android - How to add a button or textView inside a Fragment from Activity -

i see lot of questions, flow looking not achieved. basically, have simple activity class, inside attaching fragment. now, if try addview in below code snippet

            fragmentmanager fragmentmanager = getfragmentmanager();             fragmenttransaction = fragmentmanager.begintransaction();             hello = simplefragment.newinstance("hello","helloo");             fragmenttransaction.add(r.id.main, hello, "fragment");             viewgroup vg = ((viewgroup)fragmentmanager.findfragmentbyid(r.id.fragment).getview());             fragmenttransaction.commit(); 

vg returning null, because, inside fragment class, oncreateview() not yet reached. question how know activity if fragment view ready , when should addviews fragment

i have achieved similar things in past using viewtreeeobservers. seeing same issue null view references. programmatically adding new child views parent view, rather working fragment groups, same principle may work you.

    if (actionbuttionpanel.getheight() == 0) {         viewtreeobserver actionbuttonpanelobserver = actionbuttionpanel.getviewtreeobserver();         actionbuttonpanelobserver.addongloballayoutlistener(new viewtreeobserver.ongloballayoutlistener() {             @override             public void ongloballayout() {                 viewtreeobserver obs = getview().findviewbyid(r.id.llexamdetailinteractionbar).getviewtreeobserver();                  if (build.version.sdk_int >= build.version_codes.jelly_bean) {                     obs.removeongloballayoutlistener(this);                 } else {                     obs.removeglobalonlayoutlistener(this);                 }                 addactionbuttons();             }         });     } else {         addactionbuttons();     } 

this checks panel (the parent view) not yet being laid out , has 0 height, registers observer triggered when view laid out , calls function add child views.

you can see source in context here: https://github.com/o0rebelious0o/ic2014_exics_android_app/blob/master/exics/src/main/java/rce10/ic/ac/uk/exics/fragments/examdetailfragment.java