Three-Level ExpandableListView

Working demo on Github.

First of all, we will need a custom ExpandableListView, which will adjust its size using MeasureSpec. By using the AT_MOST mode, we set the size dynamically, but with a maximum pixel size.

class CustomExpandableListView extends ExpandableListView { 
  public CustomExpandableListView(Context context) {
    super(context);     
  }
 
  protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    /*
    * Adjust height
    */
    heightMeasureSpec = MeasureSpec.makeMeasureSpec(500, MeasureSpec.AT_MOST);
    super.onMeasure(widthMeasureSpec, heightMeasureSpec);
  }  
}

The next step is to create two Adapters.

The first one, which will extend the BaseExpandableListAdapter will be responsible for showing the first level.

public class Adapter extends BaseExpandableListAdapter {
  private List<object> objects;
  private Activity activity;
  private LayoutInflater inflater;
 
  public Adapter(Activity activity, List<object> objects) {
    this.objects= objects;
    this.activity= activity;
    this.inflater= (LayoutInflater);
    activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
  }

  @Override
  public Object getChild(int groupPosition, int childPosition) {
    return objects.get(groupPosition).getObjects().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) {
  
    Object object= (Object) getChild(groupPosition, childPosition);
    CustomExpandableListView subObjects=
      (CustomExpandableListView) convertView;
    if (convertView==null) {
      subObjects= new CustomExpandableListView(activity); 
    }

    Adapter2 adapter= new Adapter2(activity, object);
    subObjects.setAdapter(adapter);

    return subObjects;
  }

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

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

  @Override
  public int getGroupCount() {
    return objects.size();
  }
 
  @Override
  public long getGroupId(int groupPosition) {
    return groupPosition;
  }
 
  @Override
  public View getGroupView(int groupPosition, boolean isExpanded,
    View convertView, ViewGroup parent) {

    Object object= (Object) getGroup(groupPosition);
    if (convertView==null) {
      convertView= inflater.inflate(R.layout.listview_element, null);
    }
  
    TextView name= (TextView) convertView.findViewById(R.id.name);
    name.setText(object.getName());

    return convertView;
  }

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

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

The second adapter, which will also extend the BaseExpandableListAdapter, will be responsible for showing the second and third levels. Note that the first adapter constructs an X number of ExpandableListViews for each level 1 group, where X is the number of level 2 groups within each level 1 group.

class Adapter2 extends BaseExpandableListAdapter {
  private Object object;
  private LayoutInflater inflater; 
  private Activity activity;
 
  public Adapter2(Activity activity, Object object) {
    this.activity= activity;
    this.object= object;
    this.inflater= (LayoutInflater);

    activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
  }

  @Override
  public Object getChild(int groupPosition, int childPosition) {
    return object.getObjects().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) {

    Object object= (Object) getChild(0, childPosition);
    if (convertView==null) {
      convertView= inflater.inflate(R.layout.listview_element, null);

      Resources r= activity.getResources();
      float px40=
        TypedValue.applyDimension(
          TypedValue.COMPLEX_UNIT_DIP, 40, r.getDisplayMetrics());
      convertView.setPadding(
        convertView.getPaddingLeft() + (int) px40,
        convertView.getPaddingTop(),
        convertView.getPaddingRight(),
        convertView.getPaddingBottom());
    }
  
    TextView name= (TextView) convertView.findViewById(R.id.name);
    name.setText(object.getName());

    return convertView;
  }

  @Override
  public int getChildrenCount(int groupPosition) {
    return object.getObjects().size();
  }

  @Override
  public Object getGroup(int groupPosition) {
    return object;
  }
 
  @Override
  public int getGroupCount() {
    return 1;
  }
 
  @Override
  public long getGroupId(int groupPosition) {
    return groupPosition;
  }
 
  @Override
  public View getGroupView(int groupPosition, boolean isExpanded,
    View convertView, ViewGroup parent) {

    if (convertView==null) {
      convertView= inflater.inflate(R.layout.listview_element, null);
      Resources r = activity.getResources();
      float px20 =
        TypedValue.applyDimension(
          TypedValue.COMPLEX_UNIT_DIP, 20, r.getDisplayMetrics());
      convertView.setPadding(
        convertView.getPaddingLeft() + (int) px20,
        convertView.getPaddingTop(),
        convertView.getPaddingRight(),
        convertView.getPaddingBottom()); 
    }

    TextView name= (TextView) convertView.findViewById(R.id.name);
    name.setText(object.getName());
  
    return convertView;
  }

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

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

Working demo on Github.