用flutter的这个库，可以解决：https://pub.dev/packages/flutter_screenutil

使用方法：

1. 在pubspec.yaml文件中，添加库，如下图：
   
2. 在main.dart中导入头文件

import 'package:flutter_screenutil/flutter_screenutil.dart';

3. 在 Widget build(BuildContext context)方法中，初始化ScreenUtilInit, 代码如下：

class _MyAppState extends State<MyApp> {
  @override
  Widget build(BuildContext context) {
    return ScreenUtilInit(
      designSize: Size(750, 1334),
      minTextAdapt: true,
      splitScreenMode: true,
      builder: (_, child) {
        return MaterialApp(
        // home: Tabs()
          initialRoute: '/',
          onGenerateRoute: onGenerateRoute,
        );
      },
    );
  }
}

4. 使用方法说明

ScreenUtil().setWidth(540)  (dart sdk>=2.6 : 540.w) //Adapted to screen width
    ScreenUtil().setHeight(200) (dart sdk>=2.6 : 200.h) //Adapted to screen height , under normal circumstances, the height still uses x.w
    ScreenUtil().radius(200)    (dart sdk>=2.6 : 200.r)    //Adapt according to the smaller of width or height
    ScreenUtil().setSp(24)      (dart sdk>=2.6 : 24.sp) //Adapter font
    12.sm   //return min(12,12.sp)

    ScreenUtil().pixelRatio       //Device pixel density
    ScreenUtil().screenWidth   (dart sdk>=2.6 : 1.sw)    //Device width
    ScreenUtil().screenHeight  (dart sdk>=2.6 : 1.sh)    //Device height
    ScreenUtil().bottomBarHeight  //Bottom safe zone distance, suitable for buttons with full screen
    ScreenUtil().statusBarHeight  //Status bar height , Notch will be higher
    ScreenUtil().textScaleFactor  //System font scaling factor

    ScreenUtil().scaleWidth //The ratio of actual width to UI design
    ScreenUtil().scaleHeight //The ratio of actual height to UI design

    ScreenUtil().orientation  //Screen orientation
    0.2.sw  //0.2 times the screen width
    0.5.sh  //50% of screen height
    20.setVerticalSpacing  // SizedBox(height: 20 * scaleHeight)
    20.horizontalSpace  // SizedBox(height: 20 * scaleWidth)
    const RPadding.all(8)   // Padding.all(8.r) - take advantage of const key word
    EdgeInsets.all(10).w    //EdgeInsets.all(10.w)
    REdgeInsets.all(8)       // EdgeInsets.all(8.r)
    EdgeInsets.only(left:8,right:8).r // EdgeInsets.only(left:8.r,right:8.r).
    BoxConstraints(maxWidth: 100, minHeight: 100).w    //BoxConstraints(maxWidth: 100.w, minHeight: 100.w)
    Radius.circular(16).w          //Radius.circular(16.w)
    BorderRadius.all(Radius.circular(16)).w

5. 可以看看官方文档的说明，这里不再写了。