RadioGroup inside HorizontalScrollview, all Radiobutton get selected instead only one

Question

i'm trying to extend an HorizontalScrollView with a RadioGroup inside, when i populate the radiogroup all the button become selected on click, instead only the one i clicked

this is my class:

package widgets;

import java.util.ArrayList;

import android.annotation.SuppressLint;
import android.content.Context;
import android.graphics.drawable.Drawable;
import android.graphics.drawable.StateListDrawable;
import android.util.AttributeSet;
import android.widget.CompoundButton;
import android.widget.HorizontalScrollView;
import android.widget.RadioButton;
import android.widget.RadioGroup;
import android.widget.RadioGroup.OnCheckedChangeListener;

public class HorizontalListView extends HorizontalScrollView {

    ArrayList<String> lista = new ArrayList<String>();
    ArrayList<RadioButton> listaButton = new ArrayList<RadioButton>();
    int selected = -1;
    Drawable itemSelector;
    Context context;
    android.widget.CompoundButton.OnCheckedChangeListener listener;
    RadioGroup group;

    public HorizontalListView(Context context, AttributeSet attrs) {
        super(context, attrs);
        this.context = context;
        initView();

    }

    public HorizontalListView(Context context, ArrayList<String> stringhe, Drawable itemBackground) {
        super(context);
        this.context = context;
        this.lista = stringhe;
        this.itemSelector = itemBackground;
        initView();

    }

    @SuppressLint("NewApi")
    private synchronized void initView() {
        this.removeAllViews();
        group = new RadioGroup(getContext());
        group.setOrientation(RadioGroup.HORIZONTAL);
        LayoutParams params = new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT);
        this.addView(group, params);
        int i = 0;
        for (String string : lista) {
            RadioButton button = new RadioButton(getContext());
            if (android.os.Build.VERSION.SDK_INT < android.os.Build.VERSION_CODES.JELLY_BEAN) {
                button.setBackgroundDrawable(itemSelector);

            } else {
                button.setBackground(itemSelector);
            }

                button.setButtonDrawable(new StateListDrawable());

            button.setText(string);

            button.setTag(i);
            LayoutParams paramsButton = new LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.MATCH_PARENT);
            button.setPadding(20, 0, 20, 0);
            listaButton.add(button);
            group.addView(button, paramsButton);
            i++;

        }




    }

and this is my selector, i made all the state i need to select the correct one, but as i said the radiogroup select all the items (they also become selected if i scroll the horizontalscrollview)

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">

    <item android:state_checked="true" android:state_pressed="false"><shape xmlns:android="http://schemas.android.com/apk/res/android">
            <stroke android:width="1dp" android:color="@color/sinottica_button_border" />

            <solid android:color="@color/sinottica_button_bg_selected" />

            <padding android:bottom="2dp" android:left="5dp" android:right="5dp" android:top="2dp" />
        </shape></item>
    <item android:state_checked="false" android:state_pressed="false"><shape xmlns:android="http://schemas.android.com/apk/res/android">
            <stroke android:width="1dp" android:color="@color/sinottica_button_border" />

            <solid android:color="@color/sinottica_button_bg" />

            <padding android:bottom="2dp" android:left="5dp" android:right="5dp" android:top="2dp" />
        </shape></item>
    <item android:state_checked="true" android:state_pressed="true"><shape xmlns:android="http://schemas.android.com/apk/res/android">
            <stroke android:width="1dp" android:color="@color/sinottica_button_border" />

            <solid android:color="@color/sinottica_button_bg_selected" />

            <padding android:bottom="2dp" android:left="5dp" android:right="5dp" android:top="2dp" />
        </shape></item>
    <item android:state_checked="false" android:state_pressed="true"><shape xmlns:android="http://schemas.android.com/apk/res/android">
            <stroke android:width="1dp" android:color="@color/sinottica_button_border" />

            <solid android:color="@color/sinottica_button_bg" />

            <padding android:bottom="2dp" android:left="5dp" android:right="5dp" android:top="2dp" />
        </shape></item>

</selector>

UPDATE:

i tried to not remove the StateListDrawable, so i commented this row

 button.setButtonDrawable(new StateListDrawable());

now i have the checkbox over my textview, but while the background is out of sync with the selection, (change when i scroll, the other radiobutton in the group change their selection state when i touch one button) the checkmark is correct... there is a way to put the statelist drawable as background for the Button instead of the default (on the left of the button)