Where is the checkedRadioButtonId attribute on Android'd official doc?

Issue

I am new to phone app dev, so Android Kotlin dev is totally new to me. I am in a training session provided by the official android site.

The line below uses binding to access a selected radio button in a radio group.

val selectedId = binding.tipOptions.checkedRadioButtonId

I couldn't find checkedRadioButtonId attribute in my XML file. Instead, my XML file and the android docs has only android:checkedButton. Anyone know where checkedRadioButtonId is from? Thanks.

Solution

binding.tipOptions is a RadioGroup in your xml layout file. the RadioGroup.java has a function named getCheckedRadioButtonId(). On kotlin it can be used like checkedRadioButtonId, because kotlin getter and setter syntax: getters-and-setters

Answered By - ruby6221