将图像签名从颤振保存到设备

Question

我有这个代码，但我不知道如何将签名图像保存在设备中，有人知道我该怎么做吗？那我需要重新找回这张图片

import 'dart:convert';
import 'dart:typed_data';
import 'dart:ui' as ui;
import 'package:flutter/material.dart';
import 'package:flutter_signature_pad/flutter_signature_pad.dart';


void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);
  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  ByteData _img = ByteData(0);


  @override
  Widget build(BuildContext context) {
    var sign = Signature(
      color: Colors.red,
      strokeWidth: 5.0,
    );
    return Scaffold(
        appBar: AppBar(
          title: Text(widget.title),
        ),
        body: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.start,
            children: <Widget>[
              Expanded(child: sign),
              LimitedBox(
                  maxHeight: 200.0,
                  child: Image.memory(_img.buffer.asUint8List())),
              Padding(
                padding: EdgeInsets.all(25.0),
                child:
                Row(mainAxisAlignment: MainAxisAlignment.center, children: [
                  MaterialButton(
                      color: Colors.green,
                      onPressed: () async {
                        //retrieve image data, do whatever you want with it (send to server, save locally...)
                        var data = await sign
                            .getData()
                            .toByteData(format: ui.ImageByteFormat.png);
                        setState(() {
                          _img = data;
                        });
                        debugPrint("onPressed " +
                            base64.encode(data.buffer.asUint8List()));
                      },
                      child: Text("Save")),
                  MaterialButton(
                      color: Colors.grey,
                      onPressed: () {
                        sign.clear();
                        debugPrint("cleared");
                      },
                      child: Text("Clear")),
                ]),
              )
            ],
          ),
        ) // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

Answer 1

pngBytes = image.toByteData(格式: ui.ImageByteFormat.png)

现在，您必须将 pngBytes 转换为 List<int> 字节。

然后使用 File('$path/filename.png').writeAsBytesSync(pngBytes.buffer.asInt8List()) 将您的画布保存为 png 存储

这是一个例子

var pngBytes = await image.toByteData(format: ui.ImageByteFormat.png);
// requesting external storage permission
if(!(await checkPermission())) await requestPermission();

// Use plugin [path_provider] to export image to storage
Directory directory = await getExternalStorageDirectory();
String path = directory.path;
print(path);

// create directory on external storage
await Directory('$path/$directoryName').create(recursive: true);

// write to storage as a filename.png
File('$path/$directoryName/filename.png')
    .writeAsBytesSync(pngBytes.buffer.asInt8List());

完整示例请访问https://github.com/vemarav/signature

Answer 2

flutter 示例中的 Signature 小部件只是在画布上绘制路径：

  void paint(Canvas canvas, Size size) {
    var paint = Paint()
      ..color = Colors.black
      ..strokeCap = StrokeCap.round
      ..strokeWidth = 5.0;
    for (int i = 0; i < points.length - 1; i++) {
      if (points[i] != null && points[i + 1] != null)
        canvas.drawLine(points[i], points[i + 1], paint);
    }
  }

你需要找到一种方法

• 创建您自己的画布
• 在画布上绘制路径
• 渲染画布
• 将渲染导出为 png

具体步骤如下：

• 创建一个ui.PictureRecorder。
• 使用记录器创建Canvas和Size。
• 现在在画布上绘制路径。
• 以recorder.endRecording()结束录制
• 使用picture.toImage 获取ui.Image 对象
• 使用image.toByteData(format: ui.ImageByteFormat.png)获取png格式的图片字节
• 将其保存到文件，将其流式传输到服务器...

我的回答中描述了这些步骤（尽管用例不同）：Flutter how to save(re-encode) text overlay on video