I have been trying to solve a problem for a few hours now, but I failed to figure it out.i try a set adapter for expandable list view but i take this error. thanks.
"Attempt to invoke virtual method 'void android.widget.ExpandableListView.setAdapter(android.widget.ExpandableListAdapter)' on a null object reference"
Main_Activity
public class MainActivity extends AppCompatActivity implements View.OnClickListener {
Button b1;
private ResideMenu resideMenu;
private Context mContext;
private ResideMenuItem itemAnasayfa;
private ResideMenuItem itemRastgele;
private ResideMenuItem itemEncok;
private ResideMenuItem itemTarifyaz;
private ExpandableListView listView;
private ExpandableListAdapter listAdapter;
private List listDataHeader;
private HashMap> listHash;
@Override
protected void onCreate(Bundle savedInstanceState) {
listView=(ExpandableListView)findViewById(R.id.exp2);
initData();
listAdapter=new com.yeni.ExpandableListAdapter(this,listDataHeader,listHash);
listView.setAdapter(listAdapter);
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mContext = this;
setUpMenu();
if (savedInstanceState == null) {
changeFragment(new F_ana_sayfa());
}
}
private void initData() {
listDataHeader=new ArrayList<>();
listHash=new HashMap<>();
listDataHeader.add("et");
listDataHeader.add("tavuk");
listDataHeader.add("sebze");
listDataHeader.add("diger");
List l_et=new ArrayList<>();
l_et.add("kemikli");
l_et.add("kuşbaşı");
List l_tavuk=new ArrayList<>();
l_tavuk.add("bonfile");
l_tavuk.add("but");
l_tavuk.add("bütün tavuk");
List l_sebze=new ArrayList<>();
l_sebze.add("patates");
l_sebze.add("biber");
l_sebze.add("kabak");
l_sebze.add("patlıcan");
List l_diger=new ArrayList<>();
l_diger.add("tuz");
l_diger.add("yağ");
l_diger.add("kekik");
listHash.put(listDataHeader.get(0),l_et);
listHash.put(listDataHeader.get(1),l_tavuk);
listHash.put(listDataHeader.get(2),l_sebze);
listHash.put(listDataHeader.get(3),l_diger);
}
private void setUpMenu() {
resideMenu = new ResideMenu(this);
resideMenu.setBackground(R.drawable.menu_background);
resideMenu.attachToActivity(this);
resideMenu.setMenuListener(menuListener);
resideMenu.setScaleValue(0.6f);
//create menu items;
itemAnasayfa = new ResideMenuItem(this, R.drawable.icon_home, "Ana Sayfa");
itemRastgele = new ResideMenuItem(this, R.drawable.icon_profile, "Random tarif bul");
itemEncok = new ResideMenuItem(this, R.drawable.icon_calendar, "En cok begenilenler");
itemTarifyaz = new ResideMenuItem(this, R.drawable.icon_settings, "tarif Yaz");
itemAnasayfa.setOnClickListener(this);
itemRastgele.setOnClickListener(this);
itemEncok.setOnClickListener(this);
itemTarifyaz.setOnClickListener(this);
resideMenu.addMenuItem(itemAnasayfa, ResideMenu.DIRECTION_LEFT);
resideMenu.addMenuItem(itemRastgele, ResideMenu.DIRECTION_LEFT);
resideMenu.addMenuItem(itemEncok, ResideMenu.DIRECTION_RIGHT);
resideMenu.addMenuItem(itemTarifyaz, ResideMenu.DIRECTION_RIGHT);
findViewById(R.id.title_bar_left_menu).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
resideMenu.openMenu(ResideMenu.DIRECTION_LEFT);
}
});
findViewById(R.id.title_bar_right_menu).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
resideMenu.openMenu(ResideMenu.DIRECTION_RIGHT);
}
});
}
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
return resideMenu.dispatchTouchEvent(ev);
}
@Override
public void onClick(View view) {
if (view == itemAnasayfa) {
changeFragment(new F_ana_sayfa());
} else if (view == itemRastgele) {
changeFragment(new F_rastgele_tarif());
} else if (view == itemEncok) {
changeFragment(new F_encok_beg());
} else if (view == itemTarifyaz) {
changeFragment(new F_tarif_yaz());
}
else
changeFragment(new F_ana_sayfa());
resideMenu.closeMenu();
}
private ResideMenu.OnMenuListener menuListener = new ResideMenu.OnMenuListener() {
@Override
public void openMenu() {
Toast.makeText(mContext, "Menu is opened!", Toast.LENGTH_SHORT).show();
}
@Override
public void closeMenu() {
Toast.makeText(mContext, "Menu is closed!", Toast.LENGTH_SHORT).show();
}
};
private void changeFragment(Fragment targetFragment) {
resideMenu.clearIgnoredViewList();
getSupportFragmentManager()
.beginTransaction()
.replace(R.id.main_fragment, targetFragment, "fragment")
.setTransitionStyle(FragmentTransaction.TRANSIT_FRAGMENT_FADE)
.commit();
}
public ResideMenu getResideMenu(){
return resideMenu;}
}
Adapter Class
public class ExpandableListAdapter extends BaseExpandableListAdapter {
private Context cont;
private List listDataHeader;
private HashMap> listHashMap;
public ExpandableListAdapter(Context cont, List listDataHeader, HashMap> listHashMap) {
this.cont = cont;
this.listDataHeader = listDataHeader;
this.listHashMap = listHashMap;
}
@Override
public int getGroupCount() {
return listDataHeader.size();
}
@Override
public int getChildrenCount(int i) {
return listHashMap.get(listDataHeader.get(i)).size();
}
@Override
public Object getGroup(int i) {
return listDataHeader.get(i);
}
@Override
public Object getChild(int i, int i1) { // i=group position i=item position
return listHashMap.get(listDataHeader.get(i)).get(i1);
}
@Override
public long getGroupId(int i) {
return i;
}
@Override
public long getChildId(int i, int i1) {
return i1;
}
@Override
public boolean hasStableIds() {
return false;
}
@Override
public View getGroupView(int i, boolean b, View view, ViewGroup viewGroup) {
String headerTitle=(String)getGroup(i);
if (view==null){
LayoutInflater inflater1=(LayoutInflater)this.cont.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
view=inflater1.inflate(R.layout.list_group,null);
}
TextView lblHeader=(TextView)view.findViewById(R.id.header);
lblHeader.setTypeface(null, Typeface.BOLD);
lblHeader.setText(headerTitle);
return view;
}
@Override
public View getChildView(int i, int i1, boolean b, View view, ViewGroup viewGroup) {
final String childText=(String)getChild(i,i1);
if (view==null){
LayoutInflater inflater1=(LayoutInflater)this.cont.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
view=inflater1.inflate(R.layout.list_item,null);
}
TextView txtListChild=(TextView)view.findViewById(R.id.list_item);
txtListChild.setText(childText);
return view;
}
@Override
public boolean isChildSelectable(int i, int i1) {
return true;
}
}
Activity_Main XML
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent">
android:layout_height="match_parent"
android:id="@+id/exp2" />
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:id="@+id/layout_top">
android:layout_height="wrap_content">
android:layout_height="28dp"
android:background="@drawable/titlebar_menu_selector"
android:id="@+id/title_bar_left_menu"
android:layout_gravity="left|center_vertical"
android:layout_marginLeft="10dp"/>
android:layout_height="wrap_content"
android:padding="7dp"
android:text="Yemek Do"
android:textSize="24sp"
android:layout_gravity="center"
android:textColor="?attr/actionModeSplitBackground" />
android:layout_height="28dp"
android:background="@drawable/titlebar_menu_selector"
android:id="@+id/title_bar_right_menu"
android:layout_gravity="right|center_vertical"
android:layout_marginRight="10dp"/>
android:layout_height="5dp"
android:background="#bcb8b8"/>
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:id="@+id/main_fragment">
android:layout_height="match_parent">
android:text="Button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="true"
android:layout_marginLeft="107dp"
android:layout_marginStart="107dp"
android:layout_marginTop="188dp"
android:id="@+id/button2" />
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_alignRight="@+id/button2"
android:layout_alignEnd="@+id/button2"
android:layout_marginTop="78dp"
android:id="@+id/button3" />
list_group.xml
android:layout_height="match_parent">
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="@+id/header" />
list_item.xml
android:layout_height="match_parent">
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="@+id/list_item" />
error_log
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.yeni, PID: 2404
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.yeni/com.yeni.MainActivity}:
java.lang.NullPointerException: Attempt to invoke virtual method 'void
android.widget.ExpandableListView.setAdapter(android.widget.ExpandableListAdapter)'
on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2646)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6077)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void
android.widget.ExpandableListView.setAdapter(android.widget.ExpandableListAdapter)'
on a null object reference
at com.yeni.MainActivity.onCreate(MainActivity.java:55)
at android.app.Activity.performCreate(Activity.java:6662)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2599)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6077)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)
Answer
what are you doing:
listView=(ExpandableListView)findViewById(R.id.exp2);
initData();
listAdapter=new com.yeni.ExpandableListAdapter(this,listDataHeader,listHash);
listView.setAdapter(listAdapter);
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
you intialize listview object before setContentView its wrong. it should be like this
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
listView=(ExpandableListView)findViewById(R.id.exp2);
initData();
listAdapter=new
com.yeni.ExpandableListAdapter(this,listDataHeader,listHash);
listView.setAdapter(listAdapter);
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