Android ExpandableListView NullPointerException in ObtainView

Question

I am trying to work with a simple ExpandableListView, and I cannot understand why I get this NPE in ObtainView. I should have only one parent and several children that should be open when the parent is clicked, but it continues to fail and shows a NullPointerException in ObtainView. Thank you very much!

Prima.java:

package com.descoper.rom; import java.util.ArrayList; import android.app.ExpandableListActivity; import android.content.Context; import android.os.Bundle; import android.view.LayoutInflater; import android.widget.ExpandableListView; public class Prima extends ExpandableListActivity { // Create ArrayList to hold parent Items and Child Items private ArrayList<String> parentItems = new ArrayList<String>(); private ArrayList<Object> childItems = new ArrayList<Object>(); @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); // Create Expandable List and set it properties ExpandableListView expandableList = getExpandableListView(); expandableList.setDividerHeight(2); expandableList.setGroupIndicator(null); expandableList.setClickable(true); // Set the Items of Parent setGroupParents(); // Set The Child Data setChildData(); // Create the Adapter Adapter adapter = new Adapter(parentItems, childItems); adapter.setInflater((LayoutInflater) getSystemService(Context.LAYOUT_INFLATER_SERVICE), this); // Set the Adapter to expandableList expandableList.setAdapter(adapter); expandableList.setOnChildClickListener(this); } // method to add parent Items public void setGroupParents() { parentItems.add("Categorii"); } // method to set child data of each parent public void setChildData() { // Add Child Items for Fruits ArrayList<String> child = new ArrayList<String>(); child.add("Apple"); child.add("Mango"); child.add("Banana"); child.add("Orange"); childItems.add(child); } } 

Adapter.java:

 package com.descoper.rom; import java.util.ArrayList; import android.app.Activity; import android.view.LayoutInflater; import android.view.View; import android.view.View.OnClickListener; import android.view.ViewGroup; import android.widget.BaseExpandableListAdapter; import android.widget.CheckedTextView; import android.widget.TextView; import android.widget.Toast; public class Adapter extends BaseExpandableListAdapter { private Activity activity; private ArrayList<Object> childtems; private LayoutInflater inflater; private ArrayList<String> parentItems, child; // constructor public Adapter(ArrayList<String> parents, ArrayList<Object> childern) { this.parentItems = parents; this.childtems = childern; } public void setInflater(LayoutInflater inflater, Activity activity) { this.inflater = inflater; this.activity = activity; } // method getChildView is called automatically for each child view. public View getChildView1(int groupPosition, final int childPosition, boolean isLastChild, View convertView, ViewGroup parent) { child = (ArrayList<String>) childtems.get(groupPosition); TextView textView = null; if (convertView == null) { convertView = inflater.inflate(R.layout.child, null); } // get the textView reference and set the value textView = (TextView) convertView.findViewById(R.id.textViewChild); textView.setText(child.get(childPosition)); // set the ClickListener to handle the click event on child item convertView.setOnClickListener(new OnClickListener() { public void onClick(View view) { Toast.makeText(activity, child.get(childPosition), Toast.LENGTH_SHORT).show(); } }); return convertView; } // method getGroupView is called automatically for each parent item public View getGroupView1(int groupPosition, boolean isExpanded, View convertView, ViewGroup parent) { if (convertView == null) { convertView = inflater.inflate(R.layout.categorii, null); } ((CheckedTextView) convertView).setText(parentItems.get(groupPosition)); ((CheckedTextView) convertView).setChecked(isExpanded); return convertView; } @Override public Object getChild(int groupPosition, int childPosition) { return null; } @Override public long getChildId(int groupPosition, int childPosition) { return 0; } @Override public int getChildrenCount(int groupPosition) { return ((ArrayList<String>) childtems.get(groupPosition)).size(); } @Override public Object getGroup(int groupPosition) { return null; } @Override public int getGroupCount() { return parentItems.size(); } @Override public void onGroupCollapsed(int groupPosition) { super.onGroupCollapsed(groupPosition); } @Override public void onGroupExpanded(int groupPosition) { super.onGroupExpanded(groupPosition); } @Override public long getGroupId(int groupPosition) { return 0; } @Override public boolean hasStableIds() { return false; } @Override public boolean isChildSelectable(int groupPosition, int childPosition) { return false; } @Override public View getGroupView(int groupPosition, boolean isExpanded, View convertView, ViewGroup parent) { // TODO Auto-generated method stub return null; } @Override public View getChildView(int groupPosition, int childPosition, boolean isLastChild, View convertView, ViewGroup parent) { // TODO Auto-generated method stub return null; } } 

parent.xml:

 <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical" android:background="@drawable/backg1" android:gravity="center|top" > <CheckedTextView xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:id="@+id/textViewGroupName" android:layout_width="wrap_content" android:layout_height="60dp" android:layout_marginLeft="5dp" android:gravity="center_vertical" android:text="Categorii" android:textSize="18dp" android:textColor="#FFFFFF" android:padding="10dp" android:textStyle="bold" /> </LinearLayout> 

child.xml:

 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="40dp" android:clickable="true" android:orientation="vertical" android:paddingLeft="40dp" > <LinearLayout android:layout_width="match_parent" android:layout_height="39dp" android:gravity="center_vertical" > <ImageView android:id="@+id/childImage" android:layout_width="30dp" android:layout_height="30dp" android:layout_margin="5dp" android:background="@drawable/ic_launcher" android:contentDescription="@null" /> <TextView android:id="@+id/textViewChild" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginLeft="5dp" android:text="Categorii" android:textSize="16sp" android:textColor="#1919A3" android:textStyle="bold" /> </LinearLayout> <View android:layout_width="match_parent" android:layout_height="1dp" android:background="@android:color/white" /> </LinearLayout> 

LogCat:

 05-19 10:18:25.180: E/AndroidRuntime(1361): FATAL EXCEPTION: main 05-19 10:18:25.180: E/AndroidRuntime(1361): Process: com.descoper.rom, PID: 1361 05-19 10:18:25.180: E/AndroidRuntime(1361): java.lang.NullPointerException 05-19 10:18:25.180: E/AndroidRuntime(1361): at android.widget.AbsListView.obtainView(AbsListView.java:2265) 05-19 10:18:25.180: E/AndroidRuntime(1361): at android.widget.ListView.makeAndAddView(ListView.java:1790) 05-19 10:18:25.180: E/AndroidRuntime(1361): at android.widget.ListView.fillDown(ListView.java:691) 05-19 10:18:25.180: E/AndroidRuntime(1361): at android.widget.ListView.fillFromTop(ListView.java:752) 05-19 10:18:25.180: E/AndroidRuntime(1361): at android.widget.ListView.layoutChildren(ListView.java:1630) 05-19 10:18:25.180: E/AndroidRuntime(1361): at android.widget.AbsListView.onLayout(AbsListView.java:2091) 05-19 10:18:25.180: E/AndroidRuntime(1361): at android.view.View.layout(View.java:14817) 05-19 10:18:25.180: E/AndroidRuntime(1361): at android.view.ViewGroup.layout(ViewGroup.java:4631) 05-19 10:18:25.180: E/AndroidRuntime(1361): at android.widget.FrameLayout.layoutChildren(FrameLayout.java:453) 05-19 10:18:25.180: E/AndroidRuntime(1361): at android.widget.FrameLayout.onLayout(FrameLayout.java:388) 05-19 10:18:25.180: E/AndroidRuntime(1361): at android.view.View.layout(View.java:14817) 05-19 10:18:25.180: E/AndroidRuntime(1361): at android.view.ViewGroup.layout(ViewGroup.java:4631) 05-19 10:18:25.180: E/AndroidRuntime(1361): at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1671) 05-19 10:18:25.180: E/AndroidRuntime(1361): at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1525) 05-19 10:18:25.180: E/AndroidRuntime(1361): at android.widget.LinearLayout.onLayout(LinearLayout.java:1434) 05-19 10:18:25.180: E/AndroidRuntime(1361): at android.view.View.layout(View.java:14817) 05-19 10:18:25.180: E/AndroidRuntime(1361): at android.view.ViewGroup.layout(ViewGroup.java:4631) 05-19 10:18:25.180: E/AndroidRuntime(1361): at android.widget.FrameLayout.layoutChildren(FrameLayout.java:453) 05-19 10:18:25.180: E/AndroidRuntime(1361): at android.widget.FrameLayout.onLayout(FrameLayout.java:388) 05-19 10:18:25.180: E/AndroidRuntime(1361): at android.view.View.layout(View.java:14817) 05-19 10:18:25.180: E/AndroidRuntime(1361): at android.view.ViewGroup.layout(ViewGroup.java:4631) 05-19 10:18:25.180: E/AndroidRuntime(1361): at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:1987) 05-19 10:18:25.180: E/AndroidRuntime(1361): at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1744) 05-19 10:18:25.180: E/AndroidRuntime(1361): at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1000) 05-19 10:18:25.180: E/AndroidRuntime(1361): at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5670) 05-19 10:18:25.180: E/AndroidRuntime(1361): at android.view.Choreographer$CallbackRecord.run(Choreographer.java:761) 05-19 10:18:25.180: E/AndroidRuntime(1361): at android.view.Choreographer.doCallbacks(Choreographer.java:574) 05-19 10:18:25.180: E/AndroidRuntime(1361): at android.view.Choreographer.doFrame(Choreographer.java:544) 05-19 10:18:25.180: E/AndroidRuntime(1361): at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:747) 05-19 10:18:25.180: E/AndroidRuntime(1361): at android.os.Handler.handleCallback(Handler.java:733) 05-19 10:18:25.180: E/AndroidRuntime(1361): at android.os.Handler.dispatchMessage(Handler.java:95) 05-19 10:18:25.180: E/AndroidRuntime(1361): at android.os.Looper.loop(Looper.java:136) 05-19 10:18:25.180: E/AndroidRuntime(1361): at android.app.ActivityThread.main(ActivityThread.java:5017) 05-19 10:18:25.180: E/AndroidRuntime(1361): at java.lang.reflect.Method.invokeNative(Native Method) 05-19 10:18:25.180: E/AndroidRuntime(1361): at java.lang.reflect.Method.invoke(Method.java:515) 05-19 10:18:25.180: E/AndroidRuntime(1361): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779) 05-19 10:18:25.180: E/AndroidRuntime(1361): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595) 05-19 10:18:25.180: E/AndroidRuntime(1361): at dalvik.system.NativeStart.main(Native Method) 

Answer 1

You are returning null from getChild() and getGroup() . You must return the appropriate groups and children from your data structures.

In addition, you return null from getChildView() and getGroupView() . Here you should return the View , which will represent the child and the Views group, respectively.

I suggest you read about Adapters and how they work.