如何在Flutter中绘制或绘制全角矩形？

Question

I want to draw an arc which automatically occupies the width of the screen. For this I tried the following code:

class ArcPainter extends CustomPainter   {


  @override
  void paint(Canvas canvas, Size size) {
    // create a bounding square, based on the centre and radius of the arc
    Rect rect = new Rect.fromPoints(new Offset(0.0, -45.0),new Offset(372.0, 45.0));


    // a fancy rainbow gradient
    final Gradient gradient = new RadialGradient(
      colors: <Color>[
        Colors.white.withOpacity(1.0),

      ],
      stops: [
        0.0,
      ],
    );

    // create the Shader from the gradient and the bounding square
    final Paint paint = new Paint()..shader = gradient.createShader(rect);

    // and draw an arc
    canvas.drawArc(rect, 0.0 , pi, true, paint);
  }

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

This does my work but I want the rect in Rect rect = new Rect.fromPoints(new Offset(0.0, -45.0),new Offset(372.0, 45.0)); to occupy the full screen width.

I already tried Rect rect = new Rect.fromLTWH(0.0, -45.0, size.width, 45.0); but the arc disappears in this case.

Answer 1

So I figured out the mistake:

I had not given any size while calling this class and thus the size.width and size.height was coming 0.

I changed the code in main build from:

new Row(
children: <Widget>[
    new CustomPaint(
    painter: new ArcPainter(),
  ],
),

To:

new Row(
children: <Widget>[
  new Container(
  width: screen_width * 1,
  height: screen_height * 0.05,
  child: 
    new CustomPaint(
    painter: new ArcPainter(),
      )
    )
  ],
),

and finally in the ArcPainter:

Rect rect = new Rect.fromPoints(new Offset(0.0, - size.height),new Offset(size.width, size.height));

Note: double screen_width = MediaQuery.of(context).size.width; double screen_height = MediaQuery.of(context).size.height;