Why does my Android Application crash after I add a listView to it? -

it ran correctly before added new code program. wanted add listview show message, doesn't work. when app gets activity, program crashes... added :

    string[] studentlist = {"zhangsan","lisi"};     listview stdlistview = (listview)findviewbyid(r.id.studentlistview);     arrayadapter<string> arrayadapter;     arrayadapter = new arrayadapter<string>(this,android.r.layout.simple_list_item_2,studentlist);     stdlistview.setadapter(arrayadapter);     stdlistview.setonitemclicklistener(new adapterview.onitemclicklistener() {         @override         public void onitemclick(adapterview<?> parent, view view, int position, long id) {             string result = parent.getitematposition(position).tostring();             alertdialog.builder choice = new alertdialog.builder(editactivity.this);             choice.settitle(result);         }     }); 

to:

    protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.activity_edit);      string[] studentlist = {"zhangsan","lisi"};     listview stdlistview = (listview)findviewbyid(r.id.studentlistview);     arrayadapter<string> arrayadapter;     arrayadapter = new arrayadapter<string>(this,android.r.layout.simple_list_item_2,studentlist);     stdlistview.setadapter(arrayadapter);     stdlistview.setonitemclicklistener(new adapterview.onitemclicklistener() {         @override         public void onitemclick(adapterview<?> parent, view view, int position, long id) {             string result = parent.getitematposition(position).tostring();             alertdialog.builder choice = new alertdialog.builder(editactivity.this);             choice.settitle(result);         }     });      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();         }     });      drawerlayout drawer = (drawerlayout) findviewbyid(r.id.drawer_layout);     actionbardrawertoggle toggle = new actionbardrawertoggle(             this, drawer, 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); } 

and following xml file of layout. , added:

    <listview     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:id="@+id/studentlistview"     android:layout_alignparentright="true"     android:layout_alignparentend="true" /> 

to:

<?xml version="1.0" encoding="utf-8"?> <relativelayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" android:paddingbottom="@dimen/activity_vertical_margin" android:paddingleft="@dimen/activity_horizontal_margin" android:paddingright="@dimen/activity_horizontal_margin" android:paddingtop="@dimen/activity_vertical_margin" app:layout_behavior="@string/appbar_scrolling_view_behavior" tools:context="n402lab.door.editactivity" tools:showin="@layout/app_bar_edit">  <listview     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:id="@+id/studentlistview"     android:layout_alignparentright="true"     android:layout_alignparentend="true" /> </relativelayout> 

after saw comment on question, tried debug myself. before didn't know how debug application. saw "you must supply resource id textview" , search solution , replace "android.r.layout.simple_list_item_2" "android.r.layout.simple_list_item_1" , works.! much!