Flutter Widget截圖

Flutter中截圖的主要類是RepaintBoundary。

廢話不多說，直接上代碼：

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();

  @override
  void initState() {
    super.initState();
    if (widget.controller != null) {
      widget.controller.setGlobalKey(globalKey);
    }
  }

  @override
  Widget 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> {
  @override
  Widget build(BuildContext context) {
    return widget.child;
  }
}

class ShotController {
  GlobalKey<_OverRepaintBoundaryState> globalKey;

  Future<Uint8List> makeImageUint8List() async {
    RenderRepaintBoundary boundary = globalKey.currentContext.findRenderObject();
    // 這個可以獲取當前設備的像素比
    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;
  }
}

測試使用：

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.
  @override
  Widget 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> {
  // 關鍵是創建Controller
  ShotController shotController = new ShotController();

  int _counter = 0;

  void _incrementCounter() async {
    setState(() {
      _counter++;
    });

    // 將widget生成Uint8List傳遞給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),
      );
    }));
  }

  @override
  Widget 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.
    );
  }
}