How to set default SELECT for radio button in radio group

Question

I had created a dynamic radio group which contain onClickListener for each radio button when click. How can i set the first item in the radio group as default selected INCLUDING the onClick action for the first item.

I had try with the code((RadioButton)radioGroup.getChildAt(0)).setChecked(true); but it only set the item as checked but did not perform any onClick action.

Below is what i done for my dynamic radio button.

public static void createRoutemapButton(final Activity activity, final List<DORouteMapInfo> list, final FlexRadioGroup flexRadioGroup, final ImageView imageView){
    LayoutInflater inflater = LayoutInflater.from(activity);

    float margin = DensityUtils.dp2px(activity, 85);
    float width = DensityUtils.getWidth(activity);

    for (final DORouteMapInfo routeMap : list) {
        final RadioButton rb = (RadioButton) inflater.inflate(R.layout.item_radiobutton_label, null);
        rb.setText(routeMap.getTitle());
        FlexboxLayout.LayoutParams params = new FlexboxLayout.LayoutParams((int) (width - margin) / 2, ViewGroup.LayoutParams.WRAP_CONTENT);
        params.setMargins(5,0,5,5);
        rb.setLayoutParams(params);
        rb.setPadding(0,10,0,10);
        flexRadioGroup.addView(rb);

        flexRadioGroup.setOnCheckedChangeListener(new FlexRadioGroup.OnCheckedChangeListener() {
            @Override
            public void onCheckedChanged(@IdRes int checkedId) {
            }
        });
        rb.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Picasso.with(activity)
                        .load(routeMap.getImageURL())
                        .fit().centerInside()
                        .into(imageView);
            }
        });
    }
}