Flutter中的全局常量，類似于swift或者kotlin中的寫法，直接上代碼：

import 'dart:ui';
import 'package:flutter/cupertino.dart';

class Global {
  // 單例
  static Global instance = Global();
  // 屏幕信息
  static MediaQueryData mediaQueryData = MediaQueryData.fromWindow(window);
  static double screenWidth = mediaQueryData.size.width;
  static double screenHeight = mediaQueryData.size.height;
  static double paddingBottom = mediaQueryData.padding.bottom;
  static double paddingTop = mediaQueryData.padding.top;

    ...

}