Android listView doesn't get update when adding new items -

i'm trying create app can add strings list activity, every time add new string list replaces old one.
how can fix this?

code list is.

 @override     protected void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         setcontentview(r.layout.activity_show_list);           button button = (button) findviewbyid(r.id.addbtn);         button.setonclicklistener(new view.onclicklistener() {             @override             public void onclick(view v) {                startactivity(new intent(showlist.this, addtolist.class));             }         });          intent = getintent();         bundle b = i.getextras();         if(b!=null) {             string texttolist = b.getstring("listtext");             list<string> stuff = new arraylist<string>();             final arrayadapter<string> adapter = new arrayadapter<>(this, android.r.layout.simple_list_item_1, stuff);             listview list = (listview) findviewbyid(r.id.listview);             list.setadapter(adapter);             adapter.add(texttolist);             adapter.notifydatasetchanged();         }      } 

the xml files code:

<relativelayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" android:paddingleft="@dimen/activity_horizontal_margin" android:paddingright="@dimen/activity_horizontal_margin" android:paddingtop="@dimen/activity_vertical_margin" android:paddingbottom="@dimen/activity_vertical_margin" tools:context=".showlist">  <button     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:text="add"     android:id="@+id/addbtn"     android:layout_alignparentbottom="true"     android:layout_centerhorizontal="true" />  <textview     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:textappearance="?android:attr/textappearancemedium"     android:text="list:"     android:id="@+id/textview"     android:layout_alignparenttop="true"     android:layout_alignparentleft="true"     android:layout_alignparentstart="true" />  <listview     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:id="@+id/listview"     android:layout_centerhorizontal="true"     android:layout_above="@+id/addbtn"     android:layout_below="@+id/textview" /> 

code file input text:

@override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.activity_add_to_list);      final bundle b = new bundle();     final intent = new intent(addtolist.this, showlist.class);     final edittext text = (edittext)this.findviewbyid(r.id.listtext);     button btn = (button) findviewbyid(r.id.btnadd);     btn.setonclicklistener(new view.onclicklistener() {         @override         public void onclick(view v) {             string s = text.gettext().tostring();             b.putstring("listtext", s);             i.putextras(b);             startactivity(i);         }     }); } 

and xml code previous peace of code:

<relativelayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" android:paddingleft="@dimen/activity_horizontal_margin" android:paddingright="@dimen/activity_horizontal_margin" android:paddingtop="@dimen/activity_vertical_margin" android:paddingbottom="@dimen/activity_vertical_margin" tools:context="com.example.mathias.listapp.addtolist">  <edittext     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:id="@+id/listtext"     android:layout_alignparenttop="true"     android:layout_margintop="100dp"     android:layout_alignparentright="true"     android:layout_alignparentend="true"     android:inputtype="text"     android:layout_alignparentleft="true"     android:layout_alignparentstart="true" />  <button     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:text="add"     android:id="@+id/btnadd"     android:layout_centervertical="true"     android:layout_centerhorizontal="true" /> 

this happens because creating new list everytime enter in activity. field in save list has "permanent" one. recommend declare static list , check if it's not null:

code list is:

public class nameofmyclass{     static list<string> stuff;     @override     protected void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         setcontentview(r.layout.activity_show_list);          if(stuff==null){             stuff = new arraylist<string>();         }          listview list = (listview) findviewbyid(r.id.listview);         button button = (button) findviewbyid(r.id.addbtn);          final arrayadapter<string> adapter = new arrayadapter<>(this, android.r.layout.simple_list_item_1, stuff);          button.setonclicklistener(new view.onclicklistener() {             @override             public void onclick(view v) {                startactivity(new intent(showlist.this, addtolist.class));             }         });          intent = getintent();         bundle b = i.getextras();         if(b!=null) {             string texttolist = b.getstring("listtext");             stuff.add(texttolist);                       }          list.setadapter(adapter);      } } 

by way there several "problems" in code:

1. you added item adapter, not list
2. you initialized listview if bundle isn't null, why? listview remain everytime, don't need initialize check
3. you created final intent in other class outside click. isn't programmatically wrong, there isn't motivation in case need it. it's better locally inside click did in first class