Checkbox geting unchecked after scrolling Custom listview...!

I Create custom listview, and put checkbox in it.

at First I check all checkbox and then I scroll down listview, then checkbox getting Unchecked.

what should I do?

CustomListItem.java

package com.example.customlistviewdemo;

import android.app.Activity;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.CheckBox;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;

public class CustomListItem extends ArrayAdapter<String> {

    private final Activity context;
    private final String[] TitleArray;
    private final String[] SubTitlearray;
    private final String[] TimeArray;
    private final Integer[] MainImageId;


    public CustomListItem(Activity context, String[] TitleArray,
            String[] SubTitlearray, String[] TimeArray, Integer[] MainImageId) {
        super(context, R.layout.list_item, TitleArray);
        this.context = context;
        this.TitleArray = TitleArray;

        this.SubTitlearray = SubTitlearray;
        this.TimeArray = TimeArray;
        this.MainImageId = MainImageId;


    }

    @Override
    public View getView(int position, View view, ViewGroup parent) {
        LayoutInflater inflater = context.getLayoutInflater();
        View rowView = inflater.inflate(R.layout.list_item, null, true);
        ImageView animal, car, environment, map1, warning1, map2, warning2, download, share, plant;
        animal = (ImageView) rowView.findViewById(R.id.imgAnimal);
        car = (ImageView) rowView.findViewById(R.id.imgCar);
        environment = (ImageView) rowView.findViewById(R.id.imgEnvironment);
        plant = (ImageView) rowView.findViewById(R.id.imgPlant);
        map1 = (ImageView) rowView.findViewById(R.id.imgMap);
        warning1 = (ImageView) rowView.findViewById(R.id.imgWarning);
        map2 = (ImageView) rowView.findViewById(R.id.imgMap2);
        warning2 = (ImageView) rowView.findViewById(R.id.imgWarining2);
        download = (ImageView) rowView.findViewById(R.id.imgDownload);
        CheckBox chk = (CheckBox) rowView.findViewById(R.id.checkbox);
        share = (ImageView) rowView.findViewById(R.id.imgShare);

        animal.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                Toast.makeText(getContext(), "Animal ImageView is Clicked",
                        5000).show();
                // TODO Auto-generated method stub

            }
        });
        car.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                Toast.makeText(getContext(), "Cars ImageView is Clicked", 5000)
                        .show();
                // TODO Auto-generated method stub

            }
        });
        environment.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                Toast.makeText(getContext(),
                        "environment ImageView is Clicked", 5000).show();
                // TODO Auto-generated method stub

            }
        });
        ------------------------------------------------------------------
                      ...........................SO on............................
                        ..........................................................

        TextView mainTitle = (TextView) rowView.findViewById(R.id.txtMainTitle);
        ImageView mainImage = (ImageView) rowView
                .findViewById(R.id.imgMainImage);

        TextView SubText = (TextView) rowView.findViewById(R.id.txtSubTitle);
        TextView TimeText = (TextView) rowView.findViewById(R.id.txtTimeTitle);

        mainTitle.setText(TitleArray[position]);
        SubText.setText(SubTitlearray[position]);
        TimeText.setText(TimeArray[position]);
        mainImage.setImageResource(MainImageId[position]);

        return rowView;
    }
}

ActivityMain.java

package com.example.customlistviewdemo;

import android.app.Activity;
import android.os.Bundle;
import android.widget.ListView;

public class MainActivity extends Activity {
    ListView list;
    String[] TitleArray = { "Testing Title1. This is MainTitle",
            "Testing Title2. This is MainTitle",
            "Testing Title3. This is MainTitle",
            "Testing Title4. This is MainTitle",
            "Testing Title5. This is MainTitle",
            "Testing Title6. This is MainTitle" };
    String[] SubTitleArray = { "Reported by Man 1", "Reported by Man 2",
            "Reported by Man 3", "Reported by Man 4", "Reported by Man 5",
            "Reported by Man 6" };

    String[] TimeArray = { "about 1 hour ago", "about 2 hour ago",
            "about 3 hour ago", "about 4 hour ago", "about 5 hour ago",
            "about 6 hour ago" };

    Integer[] MainImageId = { R.drawable.android1, R.drawable.android2,
            R.drawable.android3, R.drawable.android4, R.drawable.android5,
            R.drawable.android6 };



    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        CustomListItem adapter = new CustomListItem(MainActivity.this,
                TitleArray, SubTitleArray, TimeArray, MainImageId);
        list = (ListView) findViewById(R.id.listView1);
        list.setAdapter(adapter);

    }
}

list_item.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://ift.tt/nIICcg"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:background="#FFF"
    android:orientation="vertical" >

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginBottom="10dp" >

        <TextView
            android:id="@+id/txtMainTitle"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:text="This is Sample Text"
            android:textAppearance="?android:attr/textAppearanceLarge" />
    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical" >
    </LinearLayout>

    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="130dp" >

        <LinearLayout
            android:layout_width="150dp"
            android:layout_height="wrap_content"
            android:paddingRight="15dp" >

            <CheckBox
                android:layout_width="wrap_content"
                android:layout_height="fill_parent" />

            <ImageView
                android:id="@+id/imgMainImage"
                android:layout_width="100dp"
                android:layout_height="fill_parent" />
        </LinearLayout>

        <LinearLayout
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            android:orientation="vertical" >

            <TextView
                android:id="@+id/txtSubTitle"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginBottom="5dp"
                android:text="This is Sample Text"
                android:textAppearance="?android:attr/textAppearanceSmall"
                android:textSize="16dp" />

            <TextView
                android:id="@+id/txtTimeTitle"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="This is Sample Text"
                android:textAppearance="?android:attr/textAppearanceSmall"
                android:textSize="12dp" />

            <HorizontalScrollView
                android:id="@+id/scrollView1"
                android:layout_width="fill_parent"
                android:layout_height="wrap_content"
                android:scrollbars="none" >

                <LinearLayout
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:layout_marginBottom="8dp"
                    android:layout_marginTop="8dp" >

                    <ImageView
                        android:id="@+id/imgAnimal"
                        android:layout_width="25dp"
                        android:layout_height="25dp"
                        android:layout_marginRight="10dp"
                        android:src="@drawable/channel_animal" />

                    <ImageView
                        android:id="@+id/imgCar"
                        android:layout_width="25dp"
                        android:layout_height="25dp"
                        android:layout_marginRight="10dp"
                        android:src="@drawable/channel_car" />

                    <ImageView
                        android:id="@+id/imgEnvironment"
                        android:layout_width="25dp"
                        android:layout_height="25dp"
                        android:layout_marginRight="10dp"
                        android:src="@drawable/channel_environment" />

                    <ImageView
                        android:id="@+id/imgPlant"
                        android:layout_width="25dp"
                        android:layout_height="25dp"
                        android:layout_marginRight="10dp"
                        android:src="@drawable/channel_plant" />

                    <ImageView
                        android:id="@+id/imgMap"
                        android:layout_width="25dp"
                        android:layout_height="25dp"
                        android:layout_marginRight="10dp"
                        android:src="@drawable/tab_icon_map" />

                    <ImageView
                        android:id="@+id/imgWarning"
                        android:layout_width="25dp"
                        android:layout_height="25dp"
                        android:layout_marginRight="10dp"
                        android:src="@drawable/warning_icon" />
                </LinearLayout>
            </HorizontalScrollView>

            <HorizontalScrollView
                android:id="@+id/scrollView2"
                android:layout_width="fill_parent"
                android:layout_height="wrap_content"
                android:scrollbars="none" >

                <LinearLayout
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content" >

                    <ImageView
                        android:id="@+id/imgMap2"
                        android:layout_width="30dp"
                        android:layout_height="30dp"
                        android:layout_marginRight="10dp"
                        android:src="@drawable/tab_icon_map" />

                    <ImageView
                        android:id="@+id/imgWarining2"
                        android:layout_width="30dp"
                        android:layout_height="30dp"
                        android:layout_marginRight="10dp"
                        android:src="@drawable/warning_icon" />

                    <ImageView
                        android:id="@+id/imgDownload"
                        android:layout_width="30dp"
                        android:layout_height="30dp"
                        android:layout_marginRight="10dp"
                        android:src="@drawable/download_icon" />

                    <ImageView
                        android:id="@+id/imgShare"
                        android:layout_width="30dp"
                        android:layout_height="30dp"
                        android:layout_marginRight="10dp"
                        android:src="@drawable/share_icon" />
                </LinearLayout>
            </HorizontalScrollView>
        </LinearLayout>
    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content" >

        <View
            android:id="@+id/view"
            android:layout_width="match_parent"
            android:layout_height="1dp"
            android:layout_toRightOf="@+id/text1"
            android:background="#FF9900" />
    </LinearLayout>

</LinearLayout>