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@rhalff
Forked from sma/example.dart
Created February 15, 2019 02:05
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A flutter example demonstrating a custom painter drawing selectable rects
class RectsExample extends StatefulWidget {
@override
_RectsExampleState createState() => _RectsExampleState();
}
class _RectsExampleState extends State<RectsExample> {
int _index = -1;
@override
Widget build(BuildContext context) {
return Scaffold(
body: Center(
child: Rects(
rects: [
Rect.fromLTRB(10, 20, 30, 40),
Rect.fromLTRB(40, 60, 80, 100),
],
selectedIndex: _index,
onSelected: (index) {
setState(() {
_index = index;
});
},
),
),
);
}
}
class Rects extends StatelessWidget {
final List<Rect> rects;
final void Function(int) onSelected;
final int selectedIndex;
const Rects({
Key key,
@required this.rects,
@required this.onSelected,
this.selectedIndex = -1,
}) : super(key: key);
@override
Widget build(BuildContext context) {
return GestureDetector(
onTapDown: (details) {
RenderBox box = context.findRenderObject();
final offset = box.globalToLocal(details.globalPosition);
final index = rects.lastIndexWhere((rect) => rect.contains(offset));
if (index != -1) {
onSelected(index);
return;
}
onSelected(-1);
},
child: CustomPaint(
size: Size(320, 240),
painter: _RectPainter(rects, selectedIndex),
),
);
}
}
class _RectPainter extends CustomPainter {
static Paint _red = Paint()..color = Colors.red;
static Paint _blue = Paint()..color = Colors.blue;
final List<Rect> rects;
final int selectedIndex;
_RectPainter(this.rects, this.selectedIndex);
@override
void paint(Canvas canvas, Size size) {
var i = 0;
for (Rect rect in rects) {
canvas.drawRect(rect, i++ == selectedIndex ? _red : _blue);
}
}
@override
bool shouldRepaint(CustomPainter oldDelegate) {
return true;
}
}
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