Flutter-在CustomPainters上获得触摸输入 [英] Flutter - Getting touch input on CustomPainters

问题描述

我有一个简单的CustomPaint / CustomPainter，它绘制了一个圆的段（下面的代码）。我已经读到我不能使用GestureDetector，因为它不是一个合适的小部件，所以获取输入的最佳方法是什么？

I have a simple CustomPaint/CustomPainter that draws a segment of a circle (code below). I've read that I can't use GestureDetector because it isn't a proper widget, so what's the best way to get input?

我会有很多东西分段在一起，所以我需要精确像素的触摸位置。

I'll have a bunch of segments together so I need pixel-accurate touch location.

我想到过两种可能性：

• 将画家放入SizedBox中并获取触摸坐标，然后手动计算它是否在路径内。但这将使很多代码加倍。


• 使用Material类和自定义BorderShape。

我的CustomPainter：

My CustomPainter:

class _SegmentPainter extends CustomPainter {
  static const offset = -pi/2;
  double start;
  double end;
  double innerRadius;
  double outerRadius;
  Color color;
  _SegmentPainter(this.start, this.end, {this.innerRadius = 0.0, this.outerRadius, this.color});

  @override bool shouldRepaint(CustomPainter oldDelegate) => this == oldDelegate;
  @override bool shouldRebuildSemantics(CustomPainter oldDelegate) => this == oldDelegate;

  @override
  void paint(Canvas canvas, Size size) {
    Path path = new Path();
    path.arcTo(Rect.fromCircle(center: new Offset(0.0, 0.0), radius: outerRadius), offset + start, end-start, true);
    path.relativeLineTo(-cos(offset + end)*(outerRadius-innerRadius), -sin(offset + end)*(outerRadius-innerRadius));
    path.arcTo(Rect.fromCircle(center: new Offset(0.0, 0.0), radius: innerRadius), offset + end, start-end, false);
    path.close();

    canvas.drawPath(path, new Paint()..color = color..style = PaintingStyle.fill);
  }
}

推荐答案

I同意您必须将CustomPainter放入具有大小的窗口小部件中。它可能是一个SizedBox，所以我在这里使用了它。幸运的是，您无需进行手动命中测试，因为CustomPainter只需进行一些重构即可为您处理。首先要注意的是，无需在每个paint（）上重建路径-可以在构造函数中构建路径。

I agree that you have to put the CustomPainter inside a widget that has size. It could be a SizedBox, so I've used that here. Luckily, you don't need to do a manual hit test as the CustomPainter can handle that for you with a little refactoring. The first thing to notice is that path doesn't need to be reconstructed on each paint() - it can be built in the constructor. This allows CustomPainter's hitTest to simply ask whether the tap is inside or outside the path.

class _SegmentPainter extends CustomPainter {
  static const offset = -pi / 2;

  double start;
  double end;
  double innerRadius;
  double outerRadius;
  Color color;

  Path path;

  _SegmentPainter(
      this.start, this.end, this.innerRadius, this.outerRadius, this.color) {
    path = new Path()
      ..arcTo(
          Rect.fromCircle(center: new Offset(0.0, 0.0), radius: outerRadius),
          offset + start,
          end - start,
          true)
      ..relativeLineTo(-cos(offset + end) * (outerRadius - innerRadius),
          -sin(offset + end) * (outerRadius - innerRadius))
      ..arcTo(
          Rect.fromCircle(center: new Offset(0.0, 0.0), radius: innerRadius),
          offset + end,
          start - end,
          false)
      ..close();
  }

  @override
  bool shouldRepaint(_SegmentPainter oldDelegate) {
    return oldDelegate.start != start ||
        oldDelegate.end != end ||
        oldDelegate.innerRadius != innerRadius ||
        oldDelegate.outerRadius != outerRadius ||
        oldDelegate.color != color;
  }

  @override
  bool shouldRebuildSemantics(_SegmentPainter oldDelegate) => true;

  @override
  void paint(Canvas canvas, Size size) {
    canvas.drawPath(
        path,
        new Paint()
          ..color = color
          ..style = PaintingStyle.fill);
  }

  @override
  bool hitTest(Offset position) {
    return path.contains(position);
  }
}

class SegmentWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new GestureDetector(
      onTap: () => print('tap'),
      child: new SizedBox(
        width: 250.0,
        height: 250.0,
        child: new CustomPaint(
          painter: new _SegmentPainter(0.0, 2.8, 150.0, 200.0, Colors.orange),
        ),
      ),
    );
  }
}

我用过Dart .. （级联）语法来清理路径。 （我认为您的应该... 测试被否定了。）我添加了一个StatelessWidget，作为 SizedBox 的主页和 GestureDetector 。

I've used Dart .. (cascade) syntax to clean up the path. (I think your should... tests were negated.) I added a StatelessWidget just as a home for the SizedBox and GestureDetector.

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