flutter - 在 Flutter 中获取没有构建上下文的类中的屏幕大小

Question

我试图在没有构建方法的自定义类中获取 flutter 的屏幕大小。如何在不使用 buildcontext 类的情况下获得屏幕大小？

以下代码:

class ShapesPainter extends CustomPainter {
  @override
  void paint(Canvas canvas, Size size) {

    BuildContext context;
    double width = MediaQuery.of(context).size.width;
    double height = MediaQuery.of(context).size.height;
    final paint = Paint();

    paint.color = Colors.deepOrange;

    var center = Offset(size.width / 2, size.height / 2);

    print(height);
    print(width);

    Rect rect = Rect.fromLTWH(0.0, 0.0, width, height);
    canvas.drawRect(rect, paint);
  }

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

给出以下错误:

The following assertion was thrown during paint(): 'package:flutter/src/widgets/media_query.dart': Failed assertion: line 689 pos 12: 'context != null': is not true.

Answer 1

可以直接通过屏幕的width和 height作为小部件的参数 ShapesPainter如果这就是你所需要的。

解决方案代码:

class ShapesPainter extends CustomPainter {

  final double width;
  final double height;

  ShapesPainter({this.width,this.height});

  @override
  void paint(Canvas canvas, Size size) {

    final paint = Paint();

    paint.color = Colors.deepOrange;

    var center = Offset(size.width / 2, size.height / 2);

    print(height);
    print(width);

    Rect rect = Rect.fromLTWH(0.0, 0.0, width, height);
    canvas.drawRect(rect, paint);
  }

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

用法:

// Wherever you'll be using it
ShapesPainter(
width: MediaQuery.of(context).size.width,
height: MediaQuery.of(context).size.height,
)