Flutter screenshot without using RepaintBoundary - android-studio

Question

I am working on a drawing app. I can get a screenshot of a widget using RepaintBoundary but I need to update it with a button which is outside. In my case, I can clear the list of points with a FlatButton but my Container is not clearing because of RepaintBoundary I need to get a screenshot of my Container without RepaintBoundary or I should update my Container from outside they both works for me. Thanks.
return
SingleChildScrollView(//physics: NeverScrollableScrollPhysics(),
child: Column(
children: <Widget>[
RepaintBoundary(
key: _signKey,
child: new Container(
width: 100.0 * MediaQuery.of(context).devicePixelRatio ,
height: 150.0 * MediaQuery.of(context).devicePixelRatio,
color: Colors.black12,
child: GestureDetector(
onPanUpdate: (DragUpdateDetails details) {
setState(() {
RenderBox object = context.findRenderObject();
Offset _localPosition =
object.globalToLocal(details.globalPosition);
points = new List.from(points)
..add(_localPosition);
});
},
onPanEnd: (DragEndDetails details) => points.add(null),
child: new CustomPaint(
painter: new DrawingPainter(points: points),
size: Size.infinite,
),
),
),
),
Row(
children: <Widget>[
FlatButton( //Button to clear container
padding: EdgeInsets.fromLTRB(20, 10, 20, 10),
shape: RoundedRectangleBorder(
borderRadius: BorderRadius.circular(8)),
color: Colors.redAccent,
textColor: Colors.black,
onPressed: (){
setState(() {
points.clear();
});
},
child: Text('Sil'),
),
],
),
],
),
);