Android Expandable List Example

4. Now create a new java class and call it “Parent”. In this class we will store the data about the parent: the  name and the children (an array list of children). After you create the class put the following code:

import java.util.ArrayList;

public class Parent {
    private String mTitle;
    private ArrayList<String> mArrayChildren;

    public String getTitle() {
        return mTitle;
    }

    public void setTitle(String title) {
        mTitle = title;
    }

    public ArrayList<String> getArrayChildren() {
        return mArrayChildren;
    }

    public void setArrayChildren(ArrayList<String> arrayChildren) {
        mArrayChildren = arrayChildren;
    }
}

5. At this step you have to create the adapter for the expandable list. To do this, create a new java class called “MyCustomAdapter” and put the following code:

import android.content.Context;
import android.database.DataSetObserver;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseExpandableListAdapter;
import android.widget.Button;
import android.widget.TextView;

import java.util.ArrayList;

public class MyCustomAdapter extends BaseExpandableListAdapter {


    private LayoutInflater inflater;
    private ArrayList<Parent> mParent;

    public MyCustomAdapter(Context context, ArrayList<Parent> parent){
        mParent = parent;
        inflater = LayoutInflater.from(context);
    }


    @Override
    //counts the number of group/parent items so the list knows how many times calls getGroupView() method
    public int getGroupCount() {
        return mParent.size();
    }

    @Override
    //counts the number of children items so the list knows how many times calls getChildView() method
    public int getChildrenCount(int i) {
        return mParent.get(i).getArrayChildren().size();
    }

    @Override
    //gets the title of each parent/group
    public Object getGroup(int i) {
        return mParent.get(i).getTitle();
    }

    @Override
    //gets the name of each item
    public Object getChild(int i, int i1) {
        return mParent.get(i).getArrayChildren().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 true;
    }

    @Override
    //in this method you must set the text to see the parent/group on the list
    public View getGroupView(int groupPosition, boolean b, View view, ViewGroup viewGroup) {

        ViewHolder holder = new ViewHolder();
        holder.groupPosition = groupPosition;

        if (view == null) {
            view = inflater.inflate(R.layout.list_item_parent, viewGroup,false);
        }

        TextView textView = (TextView) view.findViewById(R.id.list_item_text_view);
        textView.setText(getGroup(groupPosition).toString());

        view.setTag(holder);

        //return the entire view
        return view;
    }

    @Override
    //in this method you must set the text to see the children on the list
    public View getChildView(int groupPosition, int childPosition, boolean isLastChild, View view, ViewGroup viewGroup) {

        ViewHolder holder = new ViewHolder();
        holder.childPosition = childPosition;
        holder.groupPosition = groupPosition;

        if (view == null) {
            view = inflater.inflate(R.layout.list_item_child, viewGroup,false);
        }

        TextView textView = (TextView) view.findViewById(R.id.list_item_text_child);
        textView.setText(mParent.get(groupPosition).getArrayChildren().get(childPosition));

        view.setTag(holder);

        //return the entire view
        return view;
    }

    @Override
    public boolean isChildSelectable(int i, int i1) {
        return true;
    }

    @Override
    public void registerDataSetObserver(DataSetObserver observer) {
        /* used to make the notifyDataSetChanged() method work */
        super.registerDataSetObserver(observer);
    }

// Intentionally put on comment, if you need on click deactivate it
/*  @Override
    public void onClick(View view) {
        ViewHolder holder = (ViewHolder)view.getTag();
        if (view.getId() == holder.button.getId()){

           // DO YOUR ACTION
        }
    }*/


    protected class ViewHolder {
        protected int childPosition;
        protected int groupPosition;
        protected Button button;
    }
}

6. Now go to the MyActivity and put the following code:

import android.app.Activity;
import android.app.ExpandableListActivity;
import android.os.Bundle;
import android.widget.ExpandableListView;

import java.util.ArrayList;

public class MyActivity extends Activity {
    private ExpandableListView mExpandableList;

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


        mExpandableList = (ExpandableListView)findViewById(R.id.expandable_list);

        ArrayList<Parent> arrayParents = new ArrayList<Parent>();
        ArrayList<String> arrayChildren = new ArrayList<String>();

        //here we set the parents and the children
        for (int i = 0; i < 10; i++){
            //for each "i" create a new Parent object to set the title and the children
            Parent parent = new Parent();
            parent.setTitle("Parent " + i);

            arrayChildren = new ArrayList<String>();
            for (int j = 0; j < 10; j++) {
                arrayChildren.add("Child " + j);
            }
            parent.setArrayChildren(arrayChildren);

            //in this array we add the Parent object. We will use the arrayParents at the setAdapter
            arrayParents.add(parent);
        }

        //sets the adapter that provides data to the list.
        mExpandableList.setAdapter(new MyCustomAdapter(MyActivity.this,arrayParents));

    }
}

Now the result should look like this:

If you want to see the source code, please visit our GitHub repo here. There you can see a working project that might help you get started with ExpandableListView.