CheckBox checked on scroll automatically in ListView in android

I am newbie to android and have implemented a listView with checkbox and textViews,I am facing a weired issue of selection,When i am checking any of checkbox,other checkbox automatically checked and it is changed after scrolling randomly,Can anybody help me what changes should i make to fix this in my code?

ServiceAdapter

package one.tusk.stush.adapters;

import android.content.Context;
import android.content.Intent;
import android.util.SparseBooleanArray;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.CheckBox;
import android.widget.CompoundButton;
import android.widget.TextView;

import com.company.stush.R;

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

import one.tusk.stush.other.Const;

public class ServiceAdapter extends BaseAdapter {
    public ArrayList<HashMap<String, String>> contArray;
    SparseBooleanArray mArray;


    private Context mContext;
    String resnID, reson;
    Intent i;

    public ServiceAdapter(Context paramContext, ArrayList<HashMap<String, String>> contList) {
        this.mContext = paramContext;
        this.contArray = contList;
        mArray = new SparseBooleanArray(contList.size());

    }

    public int getCount() {
        return this.contArray.size();
    }

    public Object getItem(int paramInt) {
        return Integer.valueOf(paramInt);
    }

    public long getItemId(int paramInt) {
        return paramInt;
    }

    public View getView(final int paramInt, View paramView,
            ViewGroup paramViewGroup) {
        LayoutInflater localLayoutInflater = (LayoutInflater) this.mContext
                .getSystemService("layout_inflater");
        Viewholder localViewholder = null;
        Const.selectedIDs.clear();
        if (paramView == null) {
            paramView = localLayoutInflater.inflate(
                    R.layout.raw_single_contact, paramViewGroup, false);
            localViewholder = new Viewholder();

            localViewholder.tv_name = ((TextView) paramView
                    .findViewById(R.id.tv_name));
            localViewholder.chk_id = ((CheckBox) paramView
                    .findViewById(R.id.chk_id));

            paramView.setTag(localViewholder);


        } else {

            localViewholder = (Viewholder) paramView.getTag();
            localViewholder.chk_id.setOnCheckedChangeListener(null);
            localViewholder.chk_id.setChecked(mArray.get(paramInt));
        }
        localViewholder.tv_name.setText(contArray.get(paramInt).get("serviceText"));
        localViewholder.chk_id.setChecked(mArray.get(paramInt));
        //localViewholder.chk_id.setChecked(false);
        //localViewholder.chk_id .setTag(paramInt);

        localViewholder.chk_id.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {

            @Override
            public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
                try {


                    if (isChecked) {
                        Const.selectedIDs.add(contArray.get(paramInt));
                        Const.serviceArrayList.get(paramInt).put("flag", "1");
                    } else {
                        Const.selectedIDs.remove(contArray.get(paramInt));
                        Const.serviceArrayList.get(paramInt).put("flag", "0");
                    }
                }catch (Exception e){
                    e.printStackTrace();
                }

            }
        });




        return paramView;

    }

    static class Viewholder {


    TextView tv_name;
    CheckBox chk_id;


    }



}