this function is all your need for screenshot a widget and save locally:
static GlobalKey _repaintKey = GlobalKey();
Widget _yourWidget(){
return Stack(
key: _repaintKey,
children: [
],
);
}
Future<void> _takeScreenShot(context) async {
RenderRepaintBoundary boundary = _repaintKey.currentContext.findRenderObject();
ui.Image image = await boundary.toImage();
ByteData byteData = await image.toByteData(format: ui.ImageByteFormat.png);
Uint8List pngBytes = byteData.buffer.asUint8List();
final path = join(
(await getTemporaryDirectory()).path, "screenshot${DateTime.now().toIso8601String()}.png");
File imgFile = File(path);
imgFile.writeAsBytes(pngBytes).then((value) {
Navigator.of(context).pushNamed(Routes.uploadImage, arguments: value.uri.path);
}).catchError((onError) {
print(onError);
});
}