import 'dart:typed_data';
import 'dart:ui' as ui;
import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';class WidgetShot extends StatefulWidget {final Widget child;final ShotController controller;WidgetShot({@required this.child, this.controller});@override_WidgetShotState createState() => _WidgetShotState();
}class _WidgetShotState extends State<WidgetShot> {GlobalKey<_OverRepaintBoundaryState> globalKey = GlobalKey();@overridevoid initState() {super.initState();if (widget.controller != null) {widget.controller.setGlobalKey(globalKey);}}@overrideWidget build(BuildContext context) {return SingleChildScrollView(scrollDirection: Axis.vertical,child: SingleChildScrollView(scrollDirection: Axis.horizontal,child: _OverRepaintBoundary(key: globalKey,child: RepaintBoundary(child: widget.child,),),),);}
}class _OverRepaintBoundary extends StatefulWidget {final Widget child;const _OverRepaintBoundary({Key key, this.child}) : super(key: key);@override_OverRepaintBoundaryState createState() => _OverRepaintBoundaryState();
}class _OverRepaintBoundaryState extends State<_OverRepaintBoundary> {@overrideWidget build(BuildContext context) {return widget.child;}
}class ShotController {GlobalKey<_OverRepaintBoundaryState> globalKey;Future<Uint8List> makeImageUint8List() async {RenderRepaintBoundary boundary = globalKey.currentContext.findRenderObject();// 这个可以获取当前设备的像素比var dpr = ui.window.devicePixelRatio;ui.Image image = await boundary.toImage(pixelRatio: dpr);ByteData byteData = await image.toByteData(format: ui.ImageByteFormat.png);Uint8List pngBytes = byteData.buffer.asUint8List();return pngBytes;}setGlobalKey(GlobalKey<_OverRepaintBoundaryState> globalKey) {this.globalKey = globalKey;}
}

import 'dart:typed_data';import 'package:flutter/material.dart';
import 'package:flutter_app/widget_shot.dart';void main() => runApp(MyApp());class MyApp extends StatelessWidget {// This widget is the root of your application.
  @overrideWidget build(BuildContext context) {return MaterialApp(title: 'Flutter Demo',theme: ThemeData(primarySwatch: Colors.blue,),home: MyHomePage(title: 'widget shot demo'),);}
}class MyHomePage extends StatefulWidget {MyHomePage({Key key, this.title}) : super(key: key);final String title;@override_MyHomePageState createState() => _MyHomePageState();
}class _MyHomePageState extends State<MyHomePage> {// 关键是创建ControllerShotController shotController = new ShotController();int _counter = 0;void _incrementCounter() async {setState(() {_counter++;});// 将widget生成Uint8List传递给Image即可Uint8List pngBytes = await shotController.makeImageUint8List();Navigator.push(context, new MaterialPageRoute(builder: (_) {return Scaffold(appBar: AppBar(title: Text('shot widget'),),body: Image.memory(pngBytes),);}));}@overrideWidget build(BuildContext context) {return Scaffold(appBar: AppBar(title: Text(widget.title),),body: WidgetShot(controller: shotController,child: Center(child: Column(mainAxisAlignment: MainAxisAlignment.center,children: <Widget>[Text('You have pushed the button this many times:',),Offstage(offstage: true,child: Text('offstage demo'),),Text('$_counter',style: Theme.of(context).textTheme.display1,),],),),),floatingActionButton: FloatingActionButton(onPressed: _incrementCounter,tooltip: 'Increment',child: Icon(Icons.add),), // This trailing comma makes auto-formatting nicer for build methods.
    );}
}