flutter - 如何在 Flutter 中使用两个自定义画家？

Question

我做了2个定制画家

1.

class DrawTriangle1 extends CustomPainter {
  DrawTriangle1() {
    painter = Paint()
      ..shader =
          LinearGradient(colors: [Colors.red, Colors.white]).createShader(rect)
      ..style = PaintingStyle.fill;
  }

  @override
  void paint(Canvas canvas, Size size) {
    var path = Path();

    path.moveTo(0, 0);
    path.lineTo(size.width, 0);
    path.lineTo(size.width, size.height / 2);
    path.close();
    canvas.drawPath(path, painter);
  }

  @override
  bool shouldRepaint(CustomPainter oldDelegate) {
    return true;
  }
}

class DrawTriangle2 extends CustomPainter {
  DrawTriangle2() {
    painter = Paint()
      ..shader = LinearGradient(colors: [
        Color(0xfffff),
        Color(0xff076585),
      ]).createShader(rect)
      ..style = PaintingStyle.fill;
  }

  @override
  void paint(Canvas canvas, Size size) {
    var path = Path();
    path.lineTo(size.width / 2, size.height / 4);
    path.lineTo(0, size.height / 2);
    path.close();

    canvas.drawPath(path, painter);
  }

  @override
  bool shouldRepaint(CustomPainter oldDelegate) {
    return true;
  }
}

如果我使用自定义画家制作单个形状。画家从页面开始绘制它。

ListView(
          children: <Widget>[
            CustomPaint(
              painter: DrawTriangle1(),
              size: Size(MediaQuery.of(context).size.width,
          MediaQuery.of(context).size.height), ,
            )
          ],
        )

但是如果我像这样将另一个添加到列表视图中。第二个三角形从第一个屏幕的底部开始。

ListView(
          children: <Widget>[
            CustomPaint(
              painter: DrawTriangle1(),
              size: Size(MediaQuery.of(context).size.width,
                  MediaQuery.of(context).size.height),
            ),
            CustomPaint(
              painter: DrawTriangle2(),
              size: Size(MediaQuery.of(context).size.width,
                  MediaQuery.of(context).size.height),
            )
          ],
        ),

我如何使它们具有相同的起点？

Answer 1

ListView 一个接一个地构建它的每个子节点，因此如果您想在堆栈小部件方便的同一位置做一些工作，这是预期的行为。它将允许您在同一个地方绘制两个自定义画家。

因此，用 stack Widget 替换您的 ListView 小部件将解决您的问题。

Stack( //change 
          children: <Widget>[
            CustomPaint(
              painter: DrawTriangle1(),
              size: Size(MediaQuery.of(context).size.width,
                  MediaQuery.of(context).size.height),
            ),
            CustomPaint(
              painter: DrawTriangle2(),
              size: Size(MediaQuery.of(context).size.width,
                  MediaQuery.of(context).size.height),
            )
          ],
        ),

Answer 2

使用堆栈。

@override
  Widget build(BuildContext context) {
    return Stack(children: [
            CustomPaint(
              painter: DrawTriangle1(),
              size: Size(MediaQuery.of(context).size.width,
                  MediaQuery.of(context).size.height),
            ),
            CustomPaint(
              painter: DrawTriangle2(),
              size: Size(MediaQuery.of(context).size.width,
                  MediaQuery.of(context).size.height),
            )
          ]);
  }