在Dart中创建用于移动应用程序的“签名区域"(颤振) [英] Create `signature area` for mobile app in dart (flutter)

问题描述

我想创建一个像此处这样的签名区域，移动应用！

i want to create a signature area like Here with dart in a mobile app!

我尝试使用 CustomPaint 类...但是它不起作用.

I tried to use the CustomPaint class ... But it doesn't work.

有人可以帮助我吗?

推荐答案

您可以使用 GestureDetector 记录触摸和 CustomPaint 在屏幕上绘制.这里有一些提示:

You can create a signature area using GestureDetector to record touches and CustomPaint to draw on the screen. Here are a few tips:

• 使用 RenderBox.globalToLocal 来转换 DragUpdateDetails flutter/widgets/GestureDetector/onPanUpdate.html"rel =" noreferrer> GestureDetector.onPanUpdate 转换为相对坐标
• 使用 GestureDetector.onPanEnd 手势处理程序记录之间的间隔中风.
• 更改相同的List不会自动触发重新绘制，因为 c7> 构造函数参数相同.您可以通过在每次提供新点时创建一个新的List来触发重新绘制.
• 使用 Canvas.drawLine 在两个签名的每个记录点.

• Use RenderBox.globalToLocal to convert the DragUpdateDetails provided by GestureDetector.onPanUpdate into relative coordinates
• Use a GestureDetector.onPanEnd gesture handler to record the breaks between strokes.
• Mutating the same List won't automatically trigger a repaint because the CustomPainter constructor arguments are the same. You can trigger a repaint by creating a new List each time a new point is provided.
• Use Canvas.drawLine to draw a rounded line between each of the recorded points of the signature.

import 'package:flutter/material.dart';

class SignaturePainter extends CustomPainter {
  SignaturePainter(this.points);

  final List<Offset> points;

  void paint(Canvas canvas, Size size) {
    Paint paint = new 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);
    }
  }

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

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

class SignatureState extends State<Signature> {
  List<Offset> _points = <Offset>[];

  Widget build(BuildContext context) {
    return new Stack(
      children: [
        GestureDetector(
          onPanUpdate: (DragUpdateDetails details) {
            RenderBox referenceBox = context.findRenderObject();
            Offset localPosition =
                referenceBox.globalToLocal(details.globalPosition);

            setState(() {
              _points = new List.from(_points)..add(localPosition);
            });
          },
          onPanEnd: (DragEndDetails details) => _points.add(null),
        ),
        CustomPaint(painter: SignaturePainter(_points), size: Size.infinite),
      ],
    );
  }
}

class DemoApp extends StatelessWidget {
  Widget build(BuildContext context) => new Scaffold(body: new Signature());
}

void main() => runApp(new MaterialApp(home: new DemoApp()));

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