Listview with Checkbox in android studio

I am trying to create a custom listview with a checkbox and a string list of "observations" retrieved from my sqlite database. The idea is that when I click on the "retrieve" button, all checked items are shown in a toast message.

I can populate the listview through my customadapter just fine, but it doesnt seem to recognise the status of each checkbox, as no toast messages are shown, regardless of whether they are checked.

Please can someone show me where I am going wrong?

Here is my custom listview xm that I have called list_o:

<?xml version="1.0" encoding="utf-8"?>
<GridLayout xmlns:android="http://ift.tt/nIICcg"
android:layout_width="match_parent" android:layout_height="match_parent"
android:descendantFocusability="blocksDescendants"
android:id="@+id/obsgrid">

    <CheckBox
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/chkbx"
    android:layout_row="0"
    android:layout_column="0" />

   <TextView
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:textAppearance="?android:attr/textAppearanceLarge"
    android:text="Large Text"
    android:id="@+id/obs"
    android:layout_row="0"
    android:layout_column="1" />

Here is my custom adapter:

class CustomAdObs extends ArrayAdapter<String> {

private String [] observation;
private Boolean [] checked;
private Context context;

public CustomAdObs(Context context, String[] observation) {
    super(context, R.layout.list_o, observation);
    this.observation = observation;
    this.checked = checked;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    LayoutInflater siteInflater = LayoutInflater.from(getContext());
    View customView = siteInflater.inflate(R.layout.list_o, parent, false);

    TextView observationTV = (TextView) customView.findViewById(R.id.obs);
    CheckBox checkCB = (CheckBox) customView.findViewById(R.id.chkbx);

    checkCB.setTag(Integer.valueOf(position)); 

    observationTV.setText(observation[position]);
    checkCB.setChecked(checked[position]);

    return customView;
}

}

Finally here is my activity:

public class selobs extends Activity {

List< List<String> > listArray = new ArrayList< List<String> >();
List<String> array1 = new ArrayList<String>();


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
    StrictMode. setThreadPolicy(policy);
    setContentView(R.layout.activity_selobs);

    final Button retrieve= (Button) findViewById(R.id.btnret);
    final EditText txtob = (EditText) findViewById(R.id.editText23);

    filladapter();

    retrieve.setOnClickListener(
            new View.OnClickListener() {
                public void onClick(View view) {

                    ListView obsListView = (ListView) findViewById(R.id.obsList);
                    View v;

                    for (int i = 0; i < obsListView.getCount(); i++) {
                        v = obsListView.getAdapter().getView(i, null, null);
                        CheckBox check = (CheckBox) v.findViewById(R.id.chkbx);
                        TextView obsItem = (TextView) v.findViewById(R.id.obs);

                        if (check.isChecked()) {
                            String p = obsItem.getText().toString();
                            Toast.makeText(selobs.this, p, Toast.LENGTH_LONG).show();
                        }

                    }
                }
            }
    );
}


public void filladapter(){

    myDBhandler1 dbHandler;
    dbHandler = new myDBhandler1(selobs.this, null, null, 1);
    listArray = dbHandler.databaseToStringObs();

    List array1 = listArray.get(0);

    String[] observ = (String[]) array1.toArray(new String[0]);
    Boolean[] checked = new Boolean[0];
    Arrays.fill(checked, Boolean.FALSE);

    final ListAdapter ObsAdapter = new CustomAdObs(this, observ, checked);
    final ListView obsListView = (ListView) findViewById(R.id.obsList);

    obsListView.setAdapter(ObsAdapter);

    obsListView.setOnItemClickListener(
            new AdapterView.OnItemClickListener(){
                @Override
                public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                    String item = String.valueOf(parent.getItemAtPosition(position));
                    Toast.makeText(selobs.this, item, Toast.LENGTH_LONG).show();

                    TextView txtobs = (TextView) findViewById(R.id.editText23);

                    txtobs.setText(item);


                }
            }
    );


}

}