Flutter: NoSuchMethodError: The getter 'selection' was called on null - flutter

Question

I have a separate class which lays out radio buttons on the homepage in a separate class.
Radio Class:
Below is from TYPE enum which contains two values regular and nonregular:
TYPE _dtype = TYPE.regular;
Container(
child: Row(
children: <Widget>[
Container(
width: 180.0,
child: RadioListTile<TYPE>(
title: Text(
'Regular' ,
style: TextStyle(
fontSize: 20.0,
),
),
value: TYPE.regular,
groupValue: _dtype,
onChanged: (TYPE value) { setState(() { _dtype = value; }); },
),
),
Container(
width: 186.0,
child:RadioListTile<TYPE>(
title: const Text('Non Regular',
style: TextStyle(
fontSize: 20.0,
),
),
value: TYPE.nonregular,
groupValue: _dtype,
onChanged: (TYPE value) { setState(() { _dtype = value; }); },
),
),
],
),
)
i have couple of questions:
Is it possible to autosize the radio w.r.t. text in it? As without supplying width property, radio doesnot appear on screen.
Once one of the radio is selected, I want to pass the value..._dtype to homepage class to do some work. How can I do that?

Answer 1

Replace your Container with Expanded and remove the width attribute. This will automatically set each child of the row to occupy an equal amount of space.
To explain why this is necessary, RadioListTile will expand to take as much space as is available, and Container will be as big as its child if no size is specified. Since Row has infinite width and there's no width constraint between it and your RadioListTile, it's trying to expand to take up an infinite amount of width, so it won't render. Expanded automatically calculates and applies a width here, so it'll fix the issue and work well no matter the screen size.
Pass a callback function to your new widget. Flutter generally prefers sending data down the tree than up, so sending a callback function down to your button is a bit easier than sending the data up for your parent widget to handle, and it'll wind up having the same effect.
class YourRadioGrid extends StatelessWidget {
void Function(TYPE) doSomething = (t) {};
YourRadioGrid({this.doSomething});
...
onPressed: (TYPE value) {
doSomething(value);
}
}
// Then wherever in your homepage's build method this gets added:
YourRadioGrid(doSomething: (value) { /*handle the new value*/ })