先看一下效果
具体代码如下：
import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class MyApp extends StatefulWidget {
@override
_MyAppState createState() => _MyAppState();
}
class _MyAppState extends State<MyApp> {
List<Offset> _points = List<Offset>();
@override
Widget build(BuildContext context) {
return MaterialApp(
home: Scaffold(
body: Container(
child: GestureDetector(
onPanUpdate: (DragUpdateDetails details){
setState((){
RenderBox obj = context.findRenderObject();
Offset _localPosition = obj.globalToLocal(details.globalPosition);
_points = List.from(_points)..add(_localPosition);
});
},
onPanEnd: (DragEndDetails details) => _points..add(null),
child: CustomPaint(
painter: Signature(_points),
size: Size.infinite,
),
),
),
floatingActionButton: FloatingActionButton(
child: Icon(Icons.clear),
onPressed: () => _points.clear(),
),
),
);
}
}
class Signature extends CustomPainter {
List<Offset> points;
Signature(this.points);
@override
void paint(Canvas canvas, Size size) {
Paint paint = Paint()
..color = Colors.black
..strokeCap = StrokeCap.round
..strokeWidth = 5;
for (int i = 0; i < points.length-1; i++) {
if (points[i] != null && points[i+1] != null) {
canvas.drawLine(points[i], points[i+1], paint);
}
}
}
@override
bool shouldRepaint(Signature oldDelegate) => oldDelegate.points != points;
}
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