Flutter 手写板签名

代码如下：

import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'dart:ui' as UI;class HandWrittenBoard extends StatefulWidget {///手写笔颜色final Color? color;///手写笔宽度final double? width;///手写笔控制器final HandWrittenBoardController boardController;const HandWrittenBoard({Key? key, this.color, this.width, required this.boardController}): super(key: key);@override_HandWrittenBoardState createState() => _HandWrittenBoardState();
}class HandWrittenBoardController extends ChangeNotifier {late BuildContext _context;late List<Offset?> points = [];void bindContext(BuildContext context) {_context = context;}void refPoints(List<Offset?> newValue) {if (points != newValue) {points = newValue;notifyListeners();}}Future<UI.Image>? get uiImage {UI.PictureRecorder recorder = UI.PictureRecorder();Canvas canvas = Canvas(recorder);HandWrittenBoardPainter painter = HandWrittenBoardPainter(points);Size size = _context.size!;painter.paint(canvas, size);return recorder.endRecording().toImage(size.width.floor(), size.height.floor());}void clearBoard() {points.clear();notifyListeners();}
}class _HandWrittenBoardState extends State<HandWrittenBoard> {late ValueNotifier<List<Offset?>> _offsets = ValueNotifier([]);@overridevoid initState() {super.initState();widget.boardController.bindContext(context);}void _onUpdate(DragUpdateDetails details) {RenderBox? _object = context.findRenderObject() as RenderBox;Offset _locationPoints = _object.globalToLocal(details.globalPosition);_offsets.value = new List.from(_offsets.value)..add(_locationPoints);_refPoints();}void _onEnd(DragEndDetails details) {_offsets.value.add(null);_refPoints();}void _refPoints() {widget.boardController.refPoints(_offsets.value);}@overrideWidget build(BuildContext context) {return GestureDetector(onPanUpdate: _onUpdate,onPanEnd: _onEnd,child: ValueListenableBuilder(valueListenable: _offsets,builder: (BuildContext context, List<Offset?> value, Widget? child) {return CustomPaint(painter: HandWrittenBoardPainter(value,color: widget.color, width: widget.width),size: Size.infinite,);},),);}
}class HandWrittenBoardPainter extends CustomPainter {HandWrittenBoardPainter(this.points, {this.color, this.width});final List<Offset?> points;final Color? color;final double? width;@overridevoid paint(Canvas canvas, Size size) {var paint = Paint()..color = color ?? Colors.black..strokeCap = StrokeCap.square..strokeWidth = width ?? 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);}}}@overridebool shouldRepaint(CustomPainter oldDelegate) {return true;}
}

boardController 提供监听以及获取图片清除手写版方法
去玩吧

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