Adding CheckBoxes to a Custom ListView in Android

 Adding checkbox to a Custom ListView..sounds simple right?? Add a CheckBox to the layout,inflate,add to the ListView and everything's fine UNTIL you start scrolling!! Try checking a CheckBox and scroll down.You will find many more checked ones down below. Try scrollig up again and you will find even more!!! You will soon realize that the more you scroll,the CheckBoxes get jumbled up even more!! Wondering why?? The troublemaker here is convertView,which the ListView re-uses as you scroll. When you check a CheckBox,every list item that uses that specific convertView will have a checked CheckBox.

So how do you get around this??
Simple.Have a cache which saves the state of every CheckBox in the ListView.
Since a CheckBox can have only two states,checked or unchecked,a simple boolean array
will serve the purpose.

In effect,whenever a CheckBox in the ListView is checked or unchecked,its resulting state is stored in the boolean array.When the user scrolls,this boolean array is used to set the state of the CheckBox.

This is my ListView:

The layout for the list item is:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    
    <CheckBox 
        android:id="@+id/checkBox"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        />
    
    
    <ImageView 
        android:id="@+id/photo"
        android:layout_width="55dp"
        android:layout_height="70dp"
        android:layout_toRightOf="@id/checkBox"
        android:scaleType="fitXY"/>
    
    <TextView 
        android:id="@+id/name"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_toRightOf="@id/photo"
        android:layout_alignTop="@id/photo"
        android:textSize="18sp"/>
    
    <TextView 
        android:id="@+id/team"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_toRightOf="@id/photo"
        android:layout_below="@id/name"/>
    
    
    
</RelativeLayout>

My main.xml for the ListActivity:

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

<ListView 
        android:id="@android:id/list"
        android:layout_width="fill_parent"
        android:layout_height="0dp"
        android:layout_weight="1"/>
<ImageView android:id="@android:id/empty"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:src="@drawable/no_player"/>
</LinearLayout>

The CustomAdapter is where we declare the boolean array for holding the CheckBox states.
We also add an onClickListener to the CheckBox. When the user clicks a CheckBox,
if it is checked,then the listener sets the corresponding boolean array to true.Else,it is
set to false.
This boolean array sets the state of the CheckBox using the setChecked(boolean) method.

This is the CustomAdapter I used:

//define your custom adapter
private class CustomAdapter extends ArrayAdapter<HashMap<String, Object>>
{
   // boolean array for storing
   //the state of each CheckBox 
   boolean[] checkBoxState;
  
 
   ViewHolder viewHolder;
  
   public CustomAdapter(Context context, int textViewResourceId,
   ArrayList<HashMap<String, Object>> players) {

    //let android do the initializing :)
    super(context, textViewResourceId, players); 
   
  //create the boolean array with
   //initial state as false
  checkBoxState=new boolean[players.size()];
  }


    //class for caching the views in a row  
 private class ViewHolder
 {
   ImageView photo;
   TextView name,team;
   CheckBox checkBox;
 }

  

 @Override
 public View getView(final int position, View convertView, ViewGroup parent) {

   if(convertView==null)
    {
   convertView=inflater.inflate(R.layout.players_layout, null);
   viewHolder=new ViewHolder();

    //cache the views
    viewHolder.photo=(ImageView) convertView.findViewById(R.id.photo);
    viewHolder.name=(TextView) convertView.findViewById(R.id.name);
    viewHolder.team=(TextView) convertView.findViewById(R.id.team);
    viewHolder.checkBox=(CheckBox) convertView.findViewById(R.id.checkBox);

     //link the cached views to the convertview
    convertView.setTag( viewHolder);
   

  }
  else
   viewHolder=(ViewHolder) convertView.getTag();

           
  int photoId=(Integer) players.get(position).get("photo");

  //set the data to be displayed
  viewHolder.photo.setImageDrawable(getResources().getDrawable(photoId));
  viewHolder.name.setText(players.get(position).get("name").toString());
  viewHolder.team.setText(players.get(position).get("team").toString());
   
   //VITAL PART!!! Set the state of the 
   //CheckBox using the boolean array
        viewHolder.checkBox.setChecked(checkBoxState[position]);
            
         
           //for managing the state of the boolean
           //array according to the state of the
           //CheckBox
          
           viewHolder.checkBox.setOnClickListener(new View.OnClickListener() {
    
   public void onClick(View v) {
    if(((CheckBox)v).isChecked())
     checkBoxState[position]=true;
    else
     checkBoxState[position]=false;
     
    }
   });

   //return the view to be displayed
   return convertView;
  }

 }

Note lines 65 and 72.
In line 65,the state of the CheckBox is set to its correct state using the boolean array.
Line 72 alters the boolean array.When the user clicks on a CheckBox,the resulting state of that CheckBox is cached in the boolean array.This cached state is the one that is used to set the CheckBox to its correct state in line 65.

And this is my ListActivity  class by the way:

public class CustomListViewWithCheckBox extends ListActivity {


  //ArrayList that will hold the original Data
  ArrayList<HashMap<String, Object>> players;
  LayoutInflater inflater;

  @Override
  public void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 
 

 //get the LayoutInflater for inflating the customomView
 //this will be used in the custom adapter
 inflater=(LayoutInflater) getSystemService(Context.LAYOUT_INFLATER_SERVICE);

 //these arrays are just the data that 
 //I'll be using to populate the ArrayList
 //You can use our own methods to get the data
 String names[]={"Ronaldo","Messi","Torres","Iniesta",
    "Drogba","Gerrard","Rooney","Xavi"}; 

 String teams[]={"Real Madrid","Barcelona","Chelsea",
    "Barcelona","Chelsea","Liverpool",
    "ManU","Barcelona"};
 Integer[] photos={R.drawable.cr7,R.drawable.messi,
    R.drawable.torres,R.drawable.iniesta,
    R.drawable.drogba,R.drawable.gerrard,
    R.drawable.rooney,R.drawable.xavi};

 players=new ArrayList<HashMap<String,Object>>();

 //temporary HashMap for populating the 
 //Items in the ListView
 HashMap<String , Object> temp;

 //total number of rows in the ListView
 int noOfPlayers=names.length;

 //now populate the ArrayList players
 for(int i=0;i<noOfPlayers;i++)
 {
  temp=new HashMap<String, Object>();

  temp.put("name", names[i]);
  temp.put("team", teams[i]);    
  temp.put("photo", photos[i]);

  //add the row to the ArrayList
  players.add(temp);        
 }

 /*create the adapter
 *first param-the context
 *second param-the id of the layout file 
  you will be using to fill a row
 *third param-the set of values that
   will populate the ListView */
 final CustomAdapter adapter=new CustomAdapter(this, R.layout.players_layout,players); 
 
 //finally,set the adapter to the default ListView
 setListAdapter(adapter);
 
 
 }

This doesn't need any explanation I suppose.If you do,you are always welcome to check out
this post of mine..:).

Summing up,this is how it looks like:

public class CustomListViewWithCheckBox extends ListActivity {


  //ArrayList that will hold the original Data
  ArrayList<HashMap<String, Object>> players;
  LayoutInflater inflater;

  @Override
  public void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 
 

 //get the LayoutInflater for inflating the customomView
 //this will be used in the custom adapter
 inflater=(LayoutInflater) getSystemService(Context.LAYOUT_INFLATER_SERVICE);

 //these arrays are just the data that 
 //I'll be using to populate the ArrayList
 //You can use our own methods to get the data
 String names[]={"Ronaldo","Messi","Torres","Iniesta",
    "Drogba","Gerrard","Rooney","Xavi"}; 

 String teams[]={"Real Madrid","Barcelona","Chelsea",
    "Barcelona","Chelsea","Liverpool",
    "ManU","Barcelona"};
 Integer[] photos={R.drawable.cr7,R.drawable.messi,
    R.drawable.torres,R.drawable.iniesta,
    R.drawable.drogba,R.drawable.gerrard,
    R.drawable.rooney,R.drawable.xavi};

 players=new ArrayList<HashMap<String,Object>>();

 //temporary HashMap for populating the 
 //Items in the ListView
 HashMap<String , Object> temp;

 //total number of rows in the ListView
 int noOfPlayers=names.length;

 //now populate the ArrayList players
 for(int i=0;i<noOfPlayers;i++)
 {
  temp=new HashMap<String, Object>();

  temp.put("name", names[i]);
  temp.put("team", teams[i]);    
  temp.put("photo", photos[i]);

  //add the row to the ArrayList
  players.add(temp);        
 }

 /*create the adapter
 *first param-the context
 *second param-the id of the layout file 
  you will be using to fill a row
 *third param-the set of values that
   will populate the ListView */
 final CustomAdapter adapter=new CustomAdapter(this, R.layout.players_layout,players); 
 
 //finally,set the adapter to the default ListView
 setListAdapter(adapter);
 
 
 }


 //define your custom adapter
private class CustomAdapter extends ArrayAdapter<HashMap<String, Object>>
{
   // boolean array for storing
   //the state of each CheckBox 
   boolean[] checkBoxState;
  
 
   ViewHolder viewHolder;
  
   public CustomAdapter(Context context, int textViewResourceId,
   ArrayList<HashMap<String, Object>> players) {

    //let android do the initializing :)
    super(context, textViewResourceId, players); 
   
  //create the boolean array with
   //initial state as false
  checkBoxState=new boolean[players.size()];
  }


    //class for caching the views in a row  
 private class ViewHolder
 {
   ImageView photo;
   TextView name,team;
   CheckBox checkBox;
 }

  

 @Override
 public View getView(final int position, View convertView, ViewGroup parent) {

   if(convertView==null)
    {
   convertView=inflater.inflate(R.layout.players_layout, null);
   viewHolder=new ViewHolder();

    //cache the views
    viewHolder.photo=(ImageView) convertView.findViewById(R.id.photo);
    viewHolder.name=(TextView) convertView.findViewById(R.id.name);
    viewHolder.team=(TextView) convertView.findViewById(R.id.team);
    viewHolder.checkBox=(CheckBox) convertView.findViewById(R.id.checkBox);

     //link the cached views to the convertview
    convertView.setTag( viewHolder);
   

  }
  else
   viewHolder=(ViewHolder) convertView.getTag();

           
  int photoId=(Integer) players.get(position).get("photo");

  //set the data to be displayed
  viewHolder.photo.setImageDrawable(getResources().getDrawable(photoId));
  viewHolder.name.setText(players.get(position).get("name").toString());
  viewHolder.team.setText(players.get(position).get("team").toString());
   
   //VITAL PART!!! Set the state of the 
   //CheckBox using the boolean array
        viewHolder.checkBox.setChecked(checkBoxState[position]);
            
         
           //for managing the state of the boolean
           //array according to the state of the
           //CheckBox
          
           viewHolder.checkBox.setOnClickListener(new View.OnClickListener() {
    
   public void onClick(View v) {
    if(((CheckBox)v).isChecked())
     checkBoxState[position]=true;
    else
     checkBoxState[position]=false;
     
    }
   });

   //return the view to be displayed
   return convertView;
  }

 }
}

That's it.Happy coding.:)