Can't set OnCheckedChangeListener to a Checkbox

Question

I am trying to set a OnCheckedChangeListener to a CheckBox but my application exits in the run time. I also tried to set listeners for my TextView and I still get the same result. Can anyone help?

import android.app.ListActivity;
import android.content.Context;
import android.content.DialogInterface;
import android.content.DialogInterface.OnClickListener;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ArrayAdapter;
import android.widget.CheckBox;
import android.widget.CompoundButton;
import android.widget.CompoundButton.OnCheckedChangeListener;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;

public class ListViewActivity extends ListActivity implements OnCheckedChangeListener {

TextView label;
CheckBox checkBox;

public class MyCustomAdapter extends ArrayAdapter<String> {


public MyCustomAdapter(Context context, int textViewResourceId,
String[] objects) {
super(context, textViewResourceId, objects);

 // TODO Auto-generated constructor stub
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
// TODO Auto-generated method stub
//return super.getView(position, convertView, parent);

View row = convertView;

if(row==null){
LayoutInflater inflater=getLayoutInflater();
row=inflater.inflate(R.layout.main, parent, false); 

}  


label=(TextView)row.findViewById(R.id.weekofday);
label.setText(month[position]);
checkBox=(CheckBox)row.findViewById(R.id.checkBox);


return row;
}
}

String[] month = {
"January", "February", "March", "April",
"May", "June", "July", "August",
"September", "October", "November", "December"
};

 /** Called when the activity is first created. */
 @Override
 public void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
// setContentView(R.layout.main);
 /*setListAdapter(new ArrayAdapter<String>(this,
   R.layout.row, R.id.weekofday, DayOfWeek));*/


   setListAdapter(new MyCustomAdapter(ListViewActivity.this, R.layout.main, month));

   checkBox.setOnCheckedChangeListener(this); //my application exits here!!!!

 }





@Override
public void onCheckedChanged(CompoundButton arg0, boolean arg1) {
// TODO Auto-generated method stub
//Toast.makeText(getApplicationContext(), "box checked", Toast.LENGTH_LONG);

}


}

Answer 1

You can't set the listener for your CheckBox from the ListView like that(it will probably throw a NullPointerException), instead set the listener in the getView() method(you'll also have to keep the CheckBox status so you don't end up with strange rows status). Bellow is an example:

public class ListViewActivity extends ListActivity {

    public class MyCustomAdapter extends ArrayAdapter<String> {

        private ArrayList<Boolean> status = new ArrayList<Boolean>();

        public MyCustomAdapter(Context context, int textViewResourceId,
                String[] objects) {
            super(context, textViewResourceId, objects);
            for (int i = 0; i < objects.length; i++) {
                status.add(false);
            }
        }

        @Override
        public View getView(final int position, View convertView,
                ViewGroup parent) {
            View row = convertView;
            if (row == null) {
                LayoutInflater inflater = getLayoutInflater();
                row = inflater.inflate(R.layout.adapters_listviewactivity_row,
                        parent, false);
            }

            TextView label = (TextView) row.findViewById(R.id.weekofday);
            label.setText(month[position]);
            CheckBox checkBox = (CheckBox) row.findViewById(R.id.checkBox);
            checkBox.setOnCheckedChangeListener(new OnCheckedChangeListener() {

                @Override
                public void onCheckedChanged(CompoundButton buttonView,
                        boolean isChecked) {
                    Toast.makeText(getApplicationContext(), "" + position,
                            Toast.LENGTH_SHORT).show();
                    if (isChecked) {
                        status.set(position, true);
                    } else {
                        status.set(position, false);
                    }
                }
            });
            checkBox.setChecked(status.get(position));
            return row;
        }
    }

    String[] month = { "January", "February", "March", "April", "May", "June",
            "July", "August", "September", "October", "November", "December" };

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setListAdapter(new MyCustomAdapter(ListViewActivity.this,
                R.layout.main, month));
    }

}

For the TextView you'll have to do the same thing.