java - How to maintain fragment state when switching fragments -


in mainactivity class, have bottomnavigationview 3 tabs switch between activities (home, search, , personal). whenever click on of tabs, pulls respective fragment, believe calling new fragment each , every time.

i need these fragments maintain whatever changes made in them (similarly how instagram does). each fragment basic (newly created , unchanged), want set them in way in states saved when switch fragment , restored when go them.

below code main activity , home fragment.

public class mainactivity extends appcompatactivity { @override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.activity_main);     bottomnavigationview navigationview = (bottomnavigationview) findviewbyid(r.id.bottomnavigationview);     navigationview.setonnavigationitemselectedlistener(monnavigationitemselectedlistener);     fragmentmanager fragmentmanager = getsupportfragmentmanager();     fragmenttransaction transaction = fragmentmanager.begintransaction();     transaction.replace(r.id.content, new homefragment()).commit(); }  private bottomnavigationview.onnavigationitemselectedlistener monnavigationitemselectedlistener =         new bottomnavigationview.onnavigationitemselectedlistener(){             @override             public boolean onnavigationitemselected(@nonnull menuitem item){                 fragmentmanager fragmentmanager = getsupportfragmentmanager();                 fragmenttransaction transaction = fragmentmanager.begintransaction();                 switch (item.getitemid()){                     case r.id.homeitem:                         transaction.replace(r.id.content, new homefragment()).commit();                         return true;                     case r.id.searchitem:                         transaction.replace(r.id.content, new searchfragment()).commit();                         return true;                     case r.id.personalitem:                         transaction.replace(r.id.content, new personalfragment()).commit();                         return true;                 }                 return false;             }         }; }   public class homefragment extends fragment { // todo: rename parameter arguments, choose names match private static final string arg_param1 = "param1"; private static final string arg_param2 = "param2";  // todo: rename , change types of parameters private string mparam1; private string mparam2;  private onfragmentinteractionlistener mlistener;  public homefragment() {     // required empty public constructor }  // todo: rename , change types , number of parameters public static homefragment newinstance(string param1, string param2) {     homefragment fragment = new homefragment();     bundle args = new bundle();     args.putstring(arg_param1, param1);     args.putstring(arg_param2, param2);     fragment.setarguments(args);     return fragment; }  @override public void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     if (getarguments() != null) {         mparam1 = getarguments().getstring(arg_param1);         mparam2 = getarguments().getstring(arg_param2);     } }  @override public view oncreateview(layoutinflater inflater, viewgroup container,                          bundle savedinstancestate) {     // inflate layout fragment     return inflater.inflate(r.layout.fragment_home, container, false); }  // todo: rename method, update argument , hook method ui event public void onbuttonpressed(uri uri) {     if (mlistener != null) {         mlistener.onfragmentinteraction(uri);     } }  @override public void onattach(context context) {     super.onattach(context);     if (context instanceof onfragmentinteractionlistener) {         mlistener = (onfragmentinteractionlistener) context;     } else {         toast.maketext(context, "home fragment attached", toast.length_short).show();     } }  @override public void ondetach() {     super.ondetach();     mlistener = null; }  public interface onfragmentinteractionlistener {     // todo: update argument type , name     void onfragmentinteraction(uri uri); } }

you must use transaction.hide(fragment) , transaction.show(fragment) instead of transaction.replace, since replacing delete fragment , add again, removing saved state. doing way call fragments' onpause , onreaume method, not resetting state.

hope helps!


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