How to find radio button by id in Android?

Question

I have a radio group with radio button in an xml file:

<?xml version="1.0" encoding="utf-8"?>
<RadioGroup xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:orientation="horizontal">

   <RadioButton
        android:id="@+id/btn_1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="onRadioButtonClicked" />

    <RadioButton
        android:id="@+id/btn_2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="onRadioButtonClicked" />

</RadioGroup>

How can I get a radio button by id? I tried:

RadioButton btn = (RadioButton)findViewById(R.id.btn_1)

But this throws a nullPointerException when I call setChecked() method on btn. Did I miss something?

Answer 1

You just need to call .findViewById() on RadioGroup object. If you define radio group id as radioGroup you can access individual button like this:

RadioGroup radioGroup = (RadioGroup) findViewById(R.id.radioGroup);
View radioButton = radioGroup.findViewById(R.id.btn_1);

Other useful function would be radioGroup.getChildAt(int)