Question

I am implementing Expandable List view in android and i am getting the above titled error. Please help me.

Main activity is –

package com.expand;

import android.app.Activity;
import android.os.Bundle;
import android.util.DisplayMetrics;
import android.util.Log;
import android.view.View;
import android.widget.ExpandableListView;
import android.widget.Toast;


public class MyExpandableListViewActivity extends Activity {
    /** Called when the activity is first created. */



    static final String groupElements[]= {
           "India",
           "Australia",
           "England",
           "South Africa"
         };

    static final String[][] childElements=
    {
           {
          "Sachin Tendulkar",
          "Raina",
          "Dhoni",
          "Yuvi"
           },
           {
          "Ponting",
          "Adam Gilchrist",
          "Michael Clarke"
           },
           {
          "Andrew Strauss",
          "kevin Peterson",
          "Nasser Hussain"
           },
           {
          "Graeme Smith",
          "AB de villiers",
          "Jacques Kallis"
           }
            };



    DisplayMetrics metrics;
    int width;
    ExpandableListView expandList;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        expandList = (ExpandableListView)findViewById(R.id.expandList1);
        metrics = new DisplayMetrics();

        getWindowManager().getDefaultDisplay().getMetrics(metrics);
        width = metrics.widthPixels;

        //ExpAdapter adapter = new ExpAdapter(MyExpandableListViewActivity.this, groupElements, childElements);

        expandList.setAdapter(new ExpAdapter(MyExpandableListViewActivity.this, groupElements, childElements));
        expandList.setIndicatorBounds(width - GetDipsFromPixel(50), width - GetDipsFromPixel(10));


        expandList.setOnGroupExpandListener(new ExpandableListView.OnGroupExpandListener() {

            @Override
            public void onGroupExpand(int groupPosition) {
                // TODO Auto-generated method stub

                 Log.e("onGroupExpand", "OK");
            }
        });

        expandList.setOnGroupCollapseListener(new ExpandableListView.OnGroupCollapseListener() {

            @Override
            public void onGroupCollapse(int groupPosition) {
                // TODO Auto-generated method stub

                Log.e("onGroupCollapse", "OK");

            }
        });

        expandList.setOnChildClickListener(new ExpandableListView.OnChildClickListener() {



            @Override
            public boolean onChildClick(ExpandableListView parent, View v,
                    int groupPosition, int childPosition, long id) {

                //getting the item that is selected
                //String s = (String) expandList.getItemAtPosition((int) id);

                Toast.makeText(MyExpandableListViewActivity.this, "You have selected :"  , Toast.LENGTH_SHORT).show();

                return false;
            }
        });

    }



    public int GetDipsFromPixel(float pixels)
    {
        // Get the screen's density scale
        final float scale = getResources().getDisplayMetrics().density;
        // Convert the dps to pixels, based on density scale
        return (int) (pixels * scale + 0.5f);
    }


}

ExpAdapter class is –
I have implemented the adapter in other class and have called it in mt main activity

package com.expand;

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



    public class ExpAdapter extends BaseExpandableListAdapter {

        public Context myContext;
        public String[][] childElements;
        TextView childValues;
        public String[] groupElements;


        public ExpAdapter(Context context, String[] group, String[][] childs)
        {

            this.myContext=context;
            this.groupElements = group;
            this.childElements = childs;

        }



        @Override
        public Object getChild(int groupPosition, int childPosition) {
            // TODO Auto-generated method stub
            return childElements[groupPosition][childPosition];
        }

        @Override
        public long getChildId(int groupPosition, int childPosition) {
            // TODO Auto-generated method stub

            return 0;
        }

        @Override
        public View getChildView(int groupPosition, int childPosition,
                boolean isLastChild, View convertView, ViewGroup parent) {
            // TODO Auto-generated method stub

            if(convertView==null){

                LayoutInflater inflator = (LayoutInflater)myContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
                convertView  = inflator.inflate(R.layout.child_rows, parent);

            }
            childValues = (TextView)convertView.findViewById(R.id.rowValues);
            childValues.setText(childElements[groupPosition][childPosition]);

            return convertView;
        }

        @Override
        public int getChildrenCount(int groupPosition) {
            // TODO Auto-generated method stub
            return groupElements[groupPosition].length();
        }

        @Override
        public Object getGroup(int groupPosition) {
            // TODO Auto-generated method stub
            return groupElements[groupPosition];
        }

        @Override
        public int getGroupCount() {
            // TODO Auto-generated method stub
            return groupElements.length;
        }

        @Override
        public long getGroupId(int groupPosition) {
            // TODO Auto-generated method stub
            return 0;
        }

        @Override
        public View getGroupView(int groupPosition, boolean isExpanded,
                View convertView, ViewGroup parent) {
            // TODO Auto-generated method stub

            if(convertView==null){
                LayoutInflater inflator = (LayoutInflater)myContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
                convertView = inflator.inflate(R.layout.group_rows, null);
            }
            TextView group = (TextView)convertView.findViewById(R.id.groupId);
            group.setText(groupElements[groupPosition]);

            return convertView;
        }

        @Override
        public boolean hasStableIds() {
            // TODO Auto-generated method stub
            return false;
        }

        @Override
        public boolean isChildSelectable(int groupPosition, int childPosition) {
            // TODO Auto-generated method stub
            return true;
        }




    }

main.xml-

this is the xnl that is displayed at the first by the main activity

  <?xml version="1.0" encoding="utf-8"?>
    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:orientation="vertical" >



        <ExpandableListView 
            android:id="@+id/expandList1"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            >


                 <TextView 
                android:id="@+id/android:empty"
                android:layout_width="fill_parent"
                android:layout_height="fill_parent"
                >
            </TextView>


        </ExpandableListView>


    </LinearLayout>

group_row.xml

this is the xml for the group elements

 <?xml version="1.0" encoding="utf-8"?>
    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:id="@+id/gropu_name"
        android:layout_width="fill_parent"
        android:layout_height="40dp"
        android:orientation="vertical" >


        <TextView 
            android:id="@+id/groupId"
            android:layout_height="40dp"
            android:layout_width="wrap_content"
            android:paddingLeft="30dp"
            android:gravity="center_vertical"
            android:textSize="16dp"
            android:textStyle="bold"
            />

    </LinearLayout>

child_row.xml
this is the xml for the child elements

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="40dp"
    android:orientation="horizontal" >

    <TextView
        android:id="@+id/rowValues"
        android:layout_width="wrap_content"
        android:layout_height="30dp"
        android:gravity="center_vertical"
        android:paddingLeft="50dp"
        android:textSize="12dp" />


</LinearLayout>

Answer 1

Seems like Adapterview does not allow adding new view,
I encountered same problem

Solve it by replacing following line

convertView  = inflator.inflate(R.layout.child_rows, parent);

to

convertView  = inflator.inflate(R.layout.child_rows, null);

UPDATE

Instead of not using a parent at all, you should simply tell the Inflater not to attach the inflated view to the parent with

convertView = inflator.inflate(R.layout.child_rows, parent, false); 

See also this answer.

The reason is that adapter takes care of attaching views to parent itself.