Flutter 中获取屏幕以及 Widget 的宽高

在Flutter中，获取屏幕的宽高可以通过window.physicalSize得到，而获取Widget的宽高通常是在Widget的build方法中通过context获取。

以下是示例代码：

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
 
void main() {
  runApp(MyApp());
}
 
class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: Center(
          child: MyWidget(),
        ),
      ),
    );
  }
}
 
class MyWidget extends StatefulWidget {
  @override
  _MyWidgetState createState() => _MyWidgetState();
}
 
class _MyWidgetState extends State<MyWidget> {
  double screenWidth = 0.0;
  double screenHeight = 0.0;
  double widgetWidth = 0.0;
  double widgetHeight = 0.0;
 
  @override
  void initState() {
    super.initState();
    // 获取屏幕的宽高
    WidgetsBinding.instance.addPostFrameCallback(_getScreenSize);
  }
 
  void _getScreenSize(_) {
    final size = window.physicalSize;
    screenWidth = size.width;
    screenHeight = size.height;
  }
 
  @override
  Widget build(BuildContext context) {
    return LayoutBuilder(
      builder: (context, constraints) {
        widgetWidth = constraints.maxWidth;
        widgetHeight = constraints.maxHeight;
        return Container(
          color: Colors.blue,
          child: Center(
            child: Text(
              'Screen Width: $screenWidth\nScreen Height: $screenHeight\n'
              'Widget Width: $widgetWidth\nWidget Height: $widgetHeight',
              style: TextStyle(color: Colors.white, fontSize: 18),
            ),
          ),
        );
      },
    );
  }
}

在这个示例中，_MyWidgetState类首先在initState方法中获取屏幕的宽高，然后在build方法中使用LayoutBuilder来获取MyWidget的宽高。这些值随后被显示在Text小部件中。