flutter 屏幕截图，超出屏幕截图

用于flutter 自定义截图，超出屏幕的部分也可以截取到

import 'dart:io';
import 'dart:typed_data';
import 'dart:ui';

import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';

class ScreenShotPage extends StatefulWidget {
  @override
  _ScreenShotPageState createState() => _ScreenShotPageState();
}

class _ScreenShotPageState extends State<ScreenShotPage> {
  GlobalKey _rootWidgetKey = GlobalKey();

  @override
  Widget build(BuildContext context) {
    return Material(
      child: Scaffold(
        appBar: AppBar(title: Text('屏幕截图')),
        body: SafeArea(
          child: Stack(
            children: <Widget>[
              Positioned(
                left: 0,
                right: 0,
                top: 0,
                bottom: 60,
                child: SingleChildScrollView(
                    scrollDirection: Axis.vertical,
                    child: RepaintBoundary(
                      key: _rootWidgetKey,
                      child: Container(
                        width: double.infinity,
                        color: Color(0xffe8eaed),
                        child: Column(children: <Widget>[Column(children: _listWidget())]),
                      ),
                    )),
              ),
              Positioned(left: 0, right: 0, bottom: 0, height: 60, child: _bottomWidget()),
            ],
          ),
        ),
      ),
    );
  }

  ///数组
  List<Widget> _listWidget() {
    List<Widget> _list = List();
    for (int index = 0; index < 20; index++) {
      _list.add(Container(height: 30, child: Center(child: Text('屏幕截图$index'))));
    }
    return _list;
  }

  ///bottomWidget
  Widget _bottomWidget() {
    return Container(
      padding: EdgeInsets.fromLTRB(16, 0, 16, 0),
      height: 60,
      color: Colors.black.withOpacity(0.8),
      child: Center(
        child: RaisedButton(
          color: Colors.blue,
          shape: RoundedRectangleBorder(borderRadius: BorderRadius.circular(28)),
          onPressed: () {
            // showLoading(msg: '图片生成中...');
            _screenshotImg();
          },
          child: Text('完成', style: TextStyle(fontSize: 16, color: Colors.white)),
        ),
      ),
    );
  }

  ///截图
  Future _screenshotImg() async {
    try {
      RenderRepaintBoundary boundary = _rootWidgetKey.currentContext.findRenderObject();
      var _dpr = window.devicePixelRatio;
      var image = await boundary.toImage(pixelRatio: _dpr);
      _getImgFilePath(image, 'root/filePath').then((filePath) {
        print('filePath:$filePath');
      });
    } catch (e) {
      print(e);
    }
  }

  /// 图片写入File
  static Future<String> _getImgFilePath(var image, String filePath) async {
    ByteData byteData = await image.toByteData(format: ImageByteFormat.png);
    Uint8List pngBytes = byteData.buffer.asUint8List();
    File file = File('$filePath/237128773298739.png');
    if (!file.existsSync()) {
      file.createSync();
    }
    file.writeAsBytesSync(pngBytes);
    return file.path;
  }
}