Expandable List View in Android

ExpandableListAdapter

It loads the data into the items associated with this view.

Some Methods used by this class:-

• (Constructor) ExpandableListAdapter(Context context,List listDataHeader,HashMap> listHashMap -> Contains context of MainActivity class, List of Headers of each group and list of items of each group.
• getgroupCount() -> returns the size of group list(header list).
• getChildrenCount() -> returns the size of items of group whose groupPosition is given.
• getGroup() -> returns the name of group whose groupPosition is given.
• getChild() -> returns the name of item (whose childPosition is given)of a group( group whose groupPosition is given)
• getGroupId() -> returns the group ID.
• getChildId()-> returns child position.
• isChildSelectable-> returns true as we want child to be selectable.
• getGroupView() -> returns the view for list group header.
• getChildView()-> returns the view for child items.

Some interfaces can be implemented by this class:-

• OnChildClickListener: When a child in the expanded list is clicked, this method is invoked.
• OnGroupClickListener: When a group header in the expanded list is clicked, this method is invoked.
• OnGroupCollapseListener: Used to notify the user when a group is collapsed
• OnGroupExpandListener: Used to notify the user when a group is expanded.

Resource files:-

We have a total of 3 resource files-

• Activity_main.xml– to create a view of the main interface of the application.
• list_group.xml-Layout file to create the header of each group.
• list_item.xml-Layout file to create a list of items of each group.

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Activity_main.xml

Create two layout resource files list_group.xml and list_item.xml

List_group.xml

List_item.xml

MainActivity.java

package com.example.expandable_listview;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.ExpandableListView;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;

public class MainActivity extends AppCompatActivity {

    private ExpandableListView listView;
    private ExpandableListAdapter listAdapter;

//We need a list to create headers/titles of each group and a HashMap to handle item list of each group which is basically a pointer of items to the header of that class.
    private List listdataheader;
    private HashMap> listHashMap;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        listView=findViewById(R.id.explv);
        initData();
        listAdapter=new ExpandableListAdapter(this,listdataheader,listHashMap);
        listView.setAdapter(listAdapter);
    }

    private void initData()
    {
        listdataheader=new ArrayList<>();
        listHashMap=new HashMap<>();
        listdataheader.add("Heading1");
        listdataheader.add("Heading2");
        listdataheader.add("Heading3");
        listdataheader.add("Heading4");

        List  ed= new ArrayList<>();
        ed.add("Example of expandable listview");

        List android=new ArrayList<>();
        android.add("SubHeading1");
        android.add("SubHeading2");
        android.add("SubHeading3");
        android.add("SubHeading4");

       List android1=new ArrayList<>();
        android1.add("SubHeading1");
        android1.add("SubHeading2");
        android1.add("SubHeading3");
        android1.add("SubHeading4");

        List  ed1= new ArrayList<>();
        ed1.add("This is expandable listview");

        listHashMap.put(listdataheader.get(0),ed);
        listHashMap.put(listdataheader.get(1),android);
        listHashMap.put(listdataheader.get(2),android1);
        listHashMap.put(listdataheader.get(3),ed1);
    }
}

Create another class ExpandableListAdapter.

We can always set items to Expandable ListView using Adapter or List Adapter.

ExpandableListAdapter.java

package com.example.expandable_listview;

import android.content.Context;
import android.graphics.Typeface;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseExpandableListAdapter;
import android.widget.TextView;

import java.lang.reflect.Constructor;
import java.util.HashMap;
import java.util.List;
import java.util.ListIterator;

public class ExpandableListAdapter extends BaseExpandableListAdapter {
    private Context context;
    private List listDataHeader;
    private HashMap> listHashMap;

    public ExpandableListAdapter(Context context,List listDataHeader,HashMap> listHashMap)
    {
        this.context=context;
        this.listDataHeader=listDataHeader;
        this.listHashMap=listHashMap;
    }
    @Override
    public int getGroupCount() {
        return listDataHeader.size();
    }

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

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

    @Override
    public Object getChild(int groupPosition, int childPosition) {
        return listHashMap.get(listDataHeader.get(groupPosition)).get(childPosition);
    }

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

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

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

    @Override
    public View getGroupView(int groupPosition, boolean isExpanded, View convertView, ViewGroup parent) {
        String header=(String)getGroup(groupPosition);
        if(convertView==null)
        {
//it gives power to embed list_group view into our xml file.
            LayoutInflater inflater= (LayoutInflater) this.context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            convertView=inflater.inflate(R.layout.list_group,null);
        }
//fetch the parent value and set the value to Textview
        TextView lbiListHeader= (TextView)convertView.findViewById(R.id.lb1ListHeader);
        lbiListHeader.setTypeface(null, Typeface.BOLD);
        lbiListHeader.setText(header);
        return convertView;
    }

    @Override
    public View getChildView(int groupPosition, int childPosition, boolean isLastChild, View convertView, ViewGroup parent) {
        final String childtext=(String)getChild(groupPosition,childPosition);
        if(convertView==null)
        {
            LayoutInflater inflater= (LayoutInflater) this.context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            convertView=inflater.inflate(R.layout.list_item,null);
        }
        TextView txtlistchild= (TextView)convertView.findViewById(R.id.lb1ListItem);
        txtlistchild.setText(childtext);
        return convertView;
    }

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

After running your application, you will see your interface like this:-

This was a simple tutorial on the Expandable ListView of Android. I hope you like this article. For any Query, comment down below.

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