flutter 繪圖

在 iOS 上，你通過 CoreGraphics 來在屏幕上繪制線條和形狀。Flutter 有一套基於 Canvas 類的不同的 API，還有 CustomPaint 和 CustomPainter這兩個類來幫助你繪圖。后者實現你在 canvas 上的繪圖算法。

想要學習如何實現一個筆跡畫筆，請參考 Collin 在 StackOverflow 上的回答。

import 'package:flutter/material.dart';
class SignaturePainter extends CustomPainter {
  SignaturePainter(this.points);

  final List<Offset> points;

  void paint(Canvas canvas, Size size) {
    var paint = Paint()
      ..color = Colors.white
      ..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);
    }
  }

  bool shouldRepaint(SignaturePainter other) => other.points != points;
}

class Signature extends StatefulWidget {
  SignatureState createState() => SignatureState();
}

class SignatureState extends State<Signature> {

  List<Offset> _points = <Offset>[];

  Widget build(BuildContext context) {
    return GestureDetector(
      onPanUpdate: (DragUpdateDetails details) {
        setState(() {
          RenderBox referenceBox = context.findRenderObject();
          Offset localPosition =
          referenceBox.globalToLocal(details.globalPosition);
          _points = List.from(_points)..add(localPosition);
        });
      },
      onPanEnd: (DragEndDetails details) => _points.add(null),
      child: CustomPaint(painter: SignaturePainter(_points), size: Size.infinite),
    );
  }
}
void main() {
  runApp(new Signature());
}

運行完以后就直接用手指畫起來吧