How to check if a radiobutton is checked in a radiogroup in Android?

If you want to check on just one RadioButton you can use the isChecked function

if(radioButton.isChecked())
{
  // is checked    
}
else
{
  // not checked
}

and if you have a RadioGroup you can use

if (radioGroup.getCheckedRadioButtonId() == -1)
{
  // no radio buttons are checked
}
else
{
  // one of the radio buttons is checked
}