Flutter - 在 CustomPainters 上获取触摸输入

Question

我有一个简单的 CustomPaint/CustomPainter 可以绘制一段圆（代码如下）。我读到我不能使用 GestureDetector 因为它不是一个合适的小部件，那么获取输入的最佳方式是什么？

我将有一堆片段放在一起，所以我需要像素精确的触摸位置。

我想到的两种可能性：

• 将painter放在SizedBox中，获取触摸坐标，手动计算是否在路径内。但这会使大量代码加倍。
• 使用 Material 类和自定义 BorderShape。这会很方便，但对我来说似乎很老套。

我的自定义画家：

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);
  }
}

Answer 1

在 CustomPaint 小部件中设置子项：Container()！

InkWell(
      child: CustomPaint(painter: HexagonPainter(center, radius, color), child: Container(),),
      onTap: (){
        print('------yumcoder---');
      },

示例：

class HexagonPaint extends StatelessWidget {
  final Offset center;
  final double radius;
  final Color color;

  HexagonPaint(this.center, this.radius, this.color);

  @override
  Widget build(BuildContext context) {
    return InkWell(
      child: CustomPaint(painter: HexagonPainter(center, radius, color), child: Container(),),
      onTap: (){
        print('------yumcoder---');
      },
    );
  }
}

class HexagonPainter extends CustomPainter {
  static const int SIDES_OF_HEXAGON = 6;
  final double radius;
  final Offset center;
  final Color color;

  HexagonPainter(this.center, this.radius, this.color);

  @override
  void paint(Canvas canvas, Size size) {
    Paint paint = Paint()..color = this.color;
    Path path = createHexagonPath();
    canvas.drawPath(path, paint);
  }

  Path createHexagonPath() {
    final path = Path();
    var angle = (math.pi * 2) / SIDES_OF_HEXAGON;
    Offset firstPoint = Offset(radius * math.cos(0.0), radius * math.sin(0.0));
    path.moveTo(firstPoint.dx + center.dx, firstPoint.dy + center.dy);
    for (int i = 1; i <= SIDES_OF_HEXAGON; i++) {
      double x = radius * math.cos(angle * i) + center.dx;
      double y = radius * math.sin(angle * i) + center.dy;
      path.lineTo(x, y);
    }
    path.close();
    return path;
  }

  @override
  bool shouldRepaint(CustomPainter oldDelegate) => false;
}

Answer 2

我开发了一个名为 touchable 用于此目的。

只需使用 CanvasTouchDetector 包裹您的 CustomPaint 小部件。它需要一个构建器函数作为参数，它需要您的 CustomPaint 小部件，如下所示。

CanvasTouchDetector(
    builder: (context) => 
        CustomPaint(
            painter: MyPainter(context)
        )
)

在您的 CustomPainter 类的 paint 方法中，创建并使用 TouchyCanvas 对象（使用从 CanvasTouchDetector 和画布获得的上下文）通过不同的手势回调绘制任何形状。

var myCanvas = TouchyCanvas(context,canvas);
myCanvas.drawRect( rect , Paint() , onTapDown: (tapDetail){
    //Do stuff here. Probably change your state and animate
});

Answer 3

我同意您必须将 CustomPainter 放在具有大小的小部件中。它可能是一个 SizedBox，所以我在这里使用了它。幸运的是，您不需要进行手动命中测试，因为 CustomPainter 可以通过一些重构来为您处理。首先要注意的是 path 不需要在每个 paint() 上重建 - 它可以在构造函数中构建。这允许 CustomPainter 的 hitTest 简单地询问点击是在路径内部还是外部。

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),
        ),
      ),
    );
  }
}

我使用 Dart ..（级联）语法来清理路径。 （我认为你的should... 测试被否定了。）我添加了一个StatelessWidget 作为SizedBox 和GestureDetector 的家。