Read index of the checked RadioButton in RadioGroup

This example demonstrate how to get the index of the checked RadioButton in RadioGroup.

package com.example.androidradiogroup;

import android.os.Bundle;
import android.widget.RadioButton;
import android.widget.RadioGroup;
import android.widget.RadioGroup.OnCheckedChangeListener;
import android.widget.TextView;
import android.app.Activity;

public class MainActivity extends Activity {
 
 RadioGroup radioGroup;
 TextView textCheckedID, textCheckedIndex;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        radioGroup = (RadioGroup)findViewById(R.id.radiogroup);
        radioGroup.setOnCheckedChangeListener(radioGroupOnCheckedChangeListener);
        
        textCheckedID = (TextView)findViewById(R.id.checkedid);
        textCheckedIndex = (TextView)findViewById(R.id.checkedindex);
        
    }
    
    OnCheckedChangeListener radioGroupOnCheckedChangeListener =
      new OnCheckedChangeListener(){

    @Override
    public void onCheckedChanged(RadioGroup group, int checkedId) {

     RadioButton checkedRadioButton = (RadioButton)radioGroup.findViewById(checkedId);
     int checkedIndex = radioGroup.indexOfChild(checkedRadioButton);
     
     textCheckedID.setText("checkedID = " + checkedId);
     textCheckedIndex.setText("checkedIndex = " + checkedIndex);
    }};

}

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity" >

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hello_world" />
    
    <TextView
        android:id="@+id/checkedid"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
    <TextView
        android:id="@+id/checkedindex"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

    <RadioGroup
        android:id="@+id/radiogroup"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical">
        <RadioButton
            android:id="@+id/option1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Option 1" />
        <RadioButton
            android:id="@+id/option2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Option 2" />
        <RadioButton
            android:id="@+id/option3"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Option 3" />
    </RadioGroup>

</LinearLayout>

Please note that you cannot assume the checkedId passed to onCheckedChanged() of OnCheckedChangeListener always same for the same button. Specially when you want to set Preference for RadioButton in RadioGroup. The ADT will re-generate the IDs base on your layout. So, after you modify the layout, the IDs will be changed. I read some posts advise keep preference of RadioButton in RadioGroup base on the checkID. Yes, it work if you will not update your APK in the furture.