如何在 Flutter 中绘制矢量形状？

Question

我们正在尝试在 Flutter 中构建一个可以在运行时更改的自定义形状矢量。

例如，我们需要一个披萨形状矢量小部件，我们可以根据变量值更改切片颜色。

我们尝试在 Flutter 中使用 canvas 和painter，但他们没有清晰和好的文档。

我们也尝试过 SVG，但不幸的是 Flutter 也不支持 SVG 标签和 SVG 视图。

Answer 1

您可以创建一个扩展 CustomPainter 的小部件

class Sky extends CustomPainter {
  @override
  void paint(Canvas canvas, Size size) {
    var rect = Offset.zero & size;
    var gradient = new RadialGradient(
      center: const Alignment(0.7, -0.6),
      radius: 0.2,
      colors: [const Color(0xFFFFFF00), const Color(0xFF0099FF)],
      stops: [0.4, 1.0],
    );
    canvas.drawRect(
      rect,
      new Paint()..shader = gradient.createShader(rect),
    );
  }

  @override
  SemanticsBuilderCallback get semanticsBuilder {
    return (Size size) {
      // Annotate a rectangle containing the picture of the sun
      // with the label "Sun". When text to speech feature is enabled on the
      // device, a user will be able to locate the sun on this picture by
      // touch.
      var rect = Offset.zero & size;
      var width = size.shortestSide * 0.4;
      rect = const Alignment(0.8, -0.9).inscribe(new Size(width, width), rect);
      return [
        new CustomPainterSemantics(
          rect: rect,
          properties: new SemanticsProperties(
            label: 'Sun',
            textDirection: TextDirection.ltr,
          ),
        ),
      ];
    };
  }

  // Since this Sky painter has no fields, it always paints
  // the same thing and semantics information is the same.
  // Therefore we return false here. If we had fields (set
  // from the constructor) then we would return true if any
  // of them differed from the same fields on the oldDelegate.
  @override
  bool shouldRepaint(Sky oldDelegate) => false;
  @override
  bool shouldRebuildSemantics(Sky oldDelegate) => false;
}

另见

• https://pub.dartlang.org/packages/flutter_svg（对 Flutter 的有限 SVG 支持）
• https://github.com/flutter/flutter/tree/master/dev/tools/vitool
• https://github.com/simolus3/fluttie（不确定这是否有效）