ExpansionTile constructor

const ExpansionTile({Key key, Widget leading, @required Widget title, Color backgroundColor, ValueChanged<bool> onExpansionChanged, List<Widget> children: const [], Widget trailing, bool initiallyExpanded: false })

Creates a single-line ListTile with a trailing button that expands or collapses the tile to reveal or hide the children. The initiallyExpanded property must be non-null.

Implementation 

const ExpansionTile({
  Key key,
  this.leading,
  @required this.title,
  this.backgroundColor,
  this.onExpansionChanged,
  this.children = const <Widget>[],
  this.trailing,
  this.initiallyExpanded = false,
}) : assert(initiallyExpanded != null),
     super(key: key);