BaseExpandableListAdapter RuntimeError NullPointerException

Question

I'm trying to view data from a database in an ExpandableListView (I'm first trying to get it working with hard coded Strings).

I've used the following example: CodeWiki ExpandableListView

But I get a Runtime error when I click on a group to get the childView.

Categories1.java

public class CategoriesActivity1 extends Activity

{

ExpandableListView eListView;
ExpandableListAdapter eListAdapter;

ArrayList<String> groups;
ArrayList<ArrayList<ArrayList<String>>> children;

 @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.categories);

        eListView = (ExpandableListView)findViewById(R.id.expandableListView1);

        loadData();

        MyExpandableListAdapter adapter = new MyExpandableListAdapter(this, groups, children);

        eListView.setAdapter(adapter);


 }



 private void loadData(){

        groups= new ArrayList<String>();
        children= new ArrayList<ArrayList<ArrayList<String>>>();

        groups.add("Group 1");
        groups.add("Group 2");
        groups.add("Group 3");

        children.add(new ArrayList<ArrayList<String>>());
        children.get(0).add(new ArrayList<String>());
        children.get(0).get(0).add("Child 1 group 1");
        children.get(0).add(new ArrayList<String>());
        children.get(0).get(1).add("Child 2 group 1");
        children.get(0).add(new ArrayList<String>());
        children.get(0).get(2).add("Child 3 group 1");

        children.add(new ArrayList<ArrayList<String>>());
        children.get(1).add(new ArrayList<String>());
        children.get(1).get(0).add("Child 1 group 2");
        children.get(1).add(new ArrayList<String>());
        children.get(1).get(1).add("Child 2 group 2");
        children.get(1).add(new ArrayList<String>());
        children.get(1).get(2).add("Child 3 group 2");

        children.add(new ArrayList<ArrayList<String>>());
        children.get(2).add(new ArrayList<String>());
        children.get(2).get(0).add("Child 1 group 3");
        children.get(2).add(new ArrayList<String>());
        children.get(2).get(1).add("Child 2 group 3");
        children.get(2).add(new ArrayList<String>());
        children.get(2).get(2).add("Child 3 group 3");
    }

}

MyExpandableListAdapter.java

public class MyExpandableListAdapter extends BaseExpandableListAdapter

{

private ArrayList<String> groups;
    private ArrayList<ArrayList<ArrayList<String>>> children;
    private Context context;

public MyExpandableListAdapter(Context context, ArrayList<String> groups, ArrayList<ArrayList<ArrayList<String>>> children)
{
    this.context = context;
    this.groups = groups;
    this.children = children;
}

@Override
public boolean areAllItemsEnabled()
{
    return true;
}

@Override
public ArrayList<String> getChild(int groupPosition, int childPosition)
{
    return children.get(groupPosition).get(childPosition);
}

@Override
public long getChildId(int groupPosition, int childPosition)
{
    return childPosition;
}

@Override
public View getChildView(int groupPosition, int childPosition,
        boolean isLastChild, View convertView, ViewGroup parent)
{
    String child = (String) ((ArrayList<String>)getChild(groupPosition, childPosition)).get(0);

    if(convertView == null)
    {
        LayoutInflater layoutInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        convertView = layoutInflater.inflate(R.layout.categories_group, null);
    }

    TextView childTxt = (TextView)convertView.findViewById(R.id.TextViewChild01);

    childTxt.setText(child);

    return convertView;
}

@Override
public int getChildrenCount(int groupPosition)
{
    return children.get(groupPosition).size();
}

@Override
public Object getGroup(int groupPosition)
{
    return groups.get(groupPosition);
}

@Override
public int getGroupCount()
{
    return groups.size();
}

@Override
public long getGroupId(int groupPosition)
{
    return groupPosition;
}

@Override
public View getGroupView(int groupPosition, boolean isExpanded,
        View convertView, ViewGroup parent)
{
    String group = (String) getGroup(groupPosition);

    if(convertView == null)
    {
        LayoutInflater layoutInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        convertView = layoutInflater.inflate(R.layout.categories_group, null);
    }

    TextView groupTxt = (TextView) convertView.findViewById(R.id.TextViewGroup);

    groupTxt.setText(group);


    return convertView;
}

@Override
public boolean hasStableIds()
{
    return true;
}

@Override
public boolean isChildSelectable(int groupPosition, int childPosition)
{
    return true;
}

}

categories_group.xml

     <?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/categoriesLLayout2"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" >

    <TextView
        android:id="@+id/TextViewGroup" 
        android:layout_width="wrap_content"
        android:layout_height="50dp"
        android:layout_marginLeft="50dp"
        android:gravity="center_vertical"
    >
    </TextView>
    <TextView
        android:id="@+id/TextViewChild01" 
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="30dp"
    >
    </TextView>
</LinearLayout>

Logcat:

03-17 15:16:13.468: E/AndroidRuntime(370): FATAL EXCEPTION: main 03-17 15:16:13.468: E/AndroidRuntime(370): java.lang.NullPointerException 03-17 15:16:13.468: E/AndroidRuntime(370): at nl.test.listing.activity.MyExpandableListAdapter.getChildView(MyExpandableListAdapter.java:64) 03-17 15:16:13.468: E/AndroidRuntime(370): at android.widget.ExpandableListConnector.getView(ExpandableListConnector.java:450) 03-17 15:16:13.468: E/AndroidRuntime(370): at android.widget.AbsListView.obtainView(AbsListView.java:1430) 03-17 15:16:13.468: E/AndroidRuntime(370): at android.widget.ListView.measureHeightOfChildren(ListView.java:1216) 03-17 15:16:13.468: E/AndroidRuntime(370): at android.widget.ListView.onMeasure(ListView.java:1127) 03-17 15:16:13.468: E/AndroidRuntime(370): at android.view.View.measure(View.java:8313) 03-17 15:16:13.468: E/AndroidRuntime(370): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3138) 03-17 15:16:13.468: E/AndroidRuntime(370): at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1017) 03-17 15:16:13.468: E/AndroidRuntime(370): at android.widget.LinearLayout.measureVertical(LinearLayout.java:386) 03-17 15:16:13.468: E/AndroidRuntime(370): at android.widget.LinearLayout.onMeasure(LinearLayout.java:309) 03-17 15:16:13.468: E/AndroidRuntime(370): at android.view.View.measure(View.java:8313) 03-17 15:16:13.468: E/AndroidRuntime(370): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3138) 03-17 15:16:13.468: E/AndroidRuntime(370): at android.widget.FrameLayout.onMeasure(FrameLayout.java:250) 03-17 15:16:13.468: E/AndroidRuntime(370): at android.view.View.measure(View.java:8313) 03-17 15:16:13.468: E/AndroidRuntime(370): at android.widget.LinearLayout.measureVertical(LinearLayout.java:531) 03-17 15:16:13.468: E/AndroidRuntime(370): at android.widget.LinearLayout.onMeasure(LinearLayout.java:309) 03-17 15:16:13.468: E/AndroidRuntime(370): at android.view.View.measure(View.java:8313) 03-17 15:16:13.468: E/AndroidRuntime(370): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3138) 03-17 15:16:13.468: E/AndroidRuntime(370): at android.widget.FrameLayout.onMeasure(FrameLayout.java:250) 03-17 15:16:13.468: E/AndroidRuntime(370): at android.view.View.measure(View.java:8313) 03-17 15:16:13.468: E/AndroidRuntime(370): at android.view.ViewRoot.performTraversals(ViewRoot.java:839) 03-17 15:16:13.468: E/AndroidRuntime(370): at android.view.ViewRoot.handleMessage(ViewRoot.java:1859) 03-17 15:16:13.468: E/AndroidRuntime(370): at android.os.Handler.dispatchMessage(Handler.java:99) 03-17 15:16:13.468: E/AndroidRuntime(370): at android.os.Looper.loop(Looper.java:123) 03-17 15:16:13.468: E/AndroidRuntime(370): at android.app.ActivityThread.main(ActivityThread.java:3683) 03-17 15:16:13.468: E/AndroidRuntime(370): at java.lang.reflect.Method.invokeNative(Native Method) 03-17 15:16:13.468: E/AndroidRuntime(370): at java.lang.reflect.Method.invoke(Method.java:507) 03-17 15:16:13.468: E/AndroidRuntime(370): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839) 03-17 15:16:13.468: E/AndroidRuntime(370): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 03-17 15:16:13.468: E/AndroidRuntime(370): at dalvik.system.NativeStart.main(Native Method)

I don't know why I get this error, looking at the example I only changed the xml values from px to dp.

Answer 1

I think the problem is at class "MyExpandableListAdapter" at line number 64. Here it seems that there is some variable is becoming null at that moment. Can you paste the code at line number 64 in this class. SO that i can assist you more.