Radio<T> class

A material design radio button.

Used to select between a number of mutually exclusive values. When one radio button in a group is selected, the other radio buttons in the group cease to be selected. The values are of type T, the type parameter of the Radio class. Enums are commonly used for this purpose.

The radio button itself does not maintain any state. Instead, selecting the radio invokes the onChanged callback, passing value as a parameter. If groupValue and value match, this radio will be selected. Most widgets will respond to onChanged by calling State.setState to update the radio button's groupValue.

Here is an example of Radio widgets wrapped in ListTiles, which is similar to what you could get with the RadioListTile widget.

The currently selected character is passed into groupValue, which is maintained by the example's State. In this case, the first Radio will start off selected because _character is initialized to SingingCharacter.lafayette.

If the second radio button is pressed, the example's state is updated with setState, updating _character to SingingCharacter.jefferson. This causes the buttons to rebuild with the updated groupValue, and therefore the selection of the second button.

Requires one of its ancestors to be a Material widget.

enum SingingCharacter { lafayette, jefferson }

// ...

SingingCharacter _character = SingingCharacter.lafayette;

Widget build(BuildContext context) {
  return Center(
    child: Column(
      children: <Widget>[
        ListTile(
          title: const Text('Lafayette'),
          leading: Radio(
            value: SingingCharacter.lafayette,
            groupValue: _character,
            onChanged: (SingingCharacter value) {
              setState(() { _character = value; });
            },
          ),
        ),
        ListTile(
          title: const Text('Thomas Jefferson'),
          leading: Radio(
            value: SingingCharacter.jefferson,
            groupValue: _character,
            onChanged: (SingingCharacter value) {
              setState(() { _character = value; });
            },
          ),
        ),
      ],
    ),
  );
}

See also:

Inheritance

Constructors

Radio({Key key, @required T value, @required T groupValue, @required ValueChanged<T> onChanged, Color activeColor, MaterialTapTargetSize materialTapTargetSize })
Creates a material design radio button. [...]
const

Properties

activeColor Color
The color to use when this radio button is selected. [...]
final
groupValue → T
The currently selected value for a group of radio buttons. [...]
final
materialTapTargetSize MaterialTapTargetSize
Configures the minimum size of the tap target. [...]
final
onChanged ValueChanged<T>
Called when the user selects this radio button. [...]
final
value → T
The value represented by this radio button.
final
hashCode int
The hash code for this object. [...]
read-only, inherited
key Key
Controls how one widget replaces another widget in the tree. [...]
final, inherited
runtimeType Type
A representation of the runtime type of the object.
read-only, inherited

Methods

createState() → _RadioState<T>
Creates the mutable state for this widget at a given location in the tree. [...]
override
createElement() StatefulElement
Creates a StatefulElement to manage this widget's location in the tree. [...]
inherited
debugDescribeChildren() List<DiagnosticsNode>
Returns a list of DiagnosticsNode objects describing this node's children. [...]
@protected, inherited
debugFillProperties(DiagnosticPropertiesBuilder properties) → void
Add additional properties associated with the node. [...]
inherited
noSuchMethod(Invocation invocation) → dynamic
Invoked when a non-existent method or property is accessed. [...]
inherited
toDiagnosticsNode({String name, DiagnosticsTreeStyle style }) DiagnosticsNode
Returns a debug representation of the object that is used by debugging tools and by DiagnosticsNode.toStringDeep. [...]
inherited
toString({DiagnosticLevel minLevel: DiagnosticLevel.debug }) String
Returns a string representation of this object.
inherited
toStringDeep({String prefixLineOne: '', String prefixOtherLines, DiagnosticLevel minLevel: DiagnosticLevel.debug }) String
Returns a string representation of this node and its descendants. [...]
inherited
toStringShallow({String joiner: ', ', DiagnosticLevel minLevel: DiagnosticLevel.debug }) String
Returns a one-line detailed description of the object. [...]
inherited
toStringShort() String
A short, textual description of this widget.
inherited

Operators

operator ==(dynamic other) bool
The equality operator. [...]
inherited