main.dart

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'package:flutter_screenutil/flutter_screenutil.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      title: 'Flutter_ScreenUtil',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    //Set the fit size (fill in the screen size of the device in the design) If the design is based on the size of the iPhone6 ​​(iPhone6 ​​750*1334)
    ScreenUtil.init(context, width: 750, height: 1334, allowFontScaling: false);

    return ExampleWidget(title: 'FlutterScreenUtil Demo');
  }
}

class ExampleWidget extends StatefulWidget {
  const ExampleWidget({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _ExampleWidgetState createState() => _ExampleWidgetState();
}

class _ExampleWidgetState extends State<ExampleWidget> {
  @override
  Widget build(BuildContext context) {
    printScreenInformation();
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: SingleChildScrollView(
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.center,
          children: <Widget>[
            Row(
              children: <Widget>[
                Container(
                  padding: EdgeInsets.all(ScreenUtil().setWidth(10)),
                  width: ScreenUtil().setWidth(375),
                  height: ScreenUtil().setHeight(200),
                  color: Colors.red,
                  child: Text(
                    'My width:${ScreenUtil().setWidth(375)}dp \n'
                    'My height:${ScreenUtil().setHeight(200)}dp',
                    style: TextStyle(
                        color: Colors.white, fontSize: ScreenUtil().setSp(24)),
                  ),
                ),
                Container(
                  padding: EdgeInsets.all(ScreenUtil().setWidth(10)),
                  width: ScreenUtil().setWidth(375),
                  height: ScreenUtil().setHeight(200),
                  color: Colors.blue,
                  child: Text(
                      'My width:${ScreenUtil().setWidth(375)}dp \n'
                      'My height:${ScreenUtil().setHeight(200)}dp',
                      style: TextStyle(
                          color: Colors.white,
                          fontSize: ScreenUtil().setSp(24))),
                ),
              ],
            ),
            Text('Device width:${ScreenUtil.screenWidth}px'),
            Text('Device height:${ScreenUtil.screenHeight}px'),
            Text('Device width:${ScreenUtil.screenWidthDp}dp'),
            Text('Device height:${ScreenUtil.screenHeightDp}dp'),
            Text('Device pixel density:${ScreenUtil.pixelRatio}'),
            Text('Bottom safe zone distance:${ScreenUtil.bottomBarHeight}dp'),
            Text('Status bar height:${ScreenUtil.statusBarHeight}dp'),
            Text(
              'Ratio of actual width dp to design draft px:${ScreenUtil().scaleWidth}',
              textAlign: TextAlign.center,
            ),
            Text(
              'Ratio of actual height dp to design draft px:${ScreenUtil().scaleHeight}',
              textAlign: TextAlign.center,
            ),
            SizedBox(
              height: ScreenUtil().setHeight(100),
            ),
            Text('System font scaling factor:${ScreenUtil.textScaleFactor}'),
            Column(
              crossAxisAlignment: CrossAxisAlignment.start,
              children: <Widget>[
                Text(
                    'My font size is 24px on the design draft and will not change with the system.',
                    style: TextStyle(
                      color: Colors.black,
                      fontSize: ScreenUtil().setSp(24),
                    )),
                Text(
                    'My font size is 24px on the design draft and will change with the system.',
                    style: TextStyle(
                        color: Colors.black,
                        fontSize: ScreenUtil()
                            .setSp(24, allowFontScalingSelf: true))),
              ],
            )
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        child: Icon(Icons.title),
        onPressed: () {
          ScreenUtil.init(context,
              width: 1500, height: 1334, allowFontScaling: false);
          setState(() {});
        },
      ),
    );
  }

  void printScreenInformation() {
    print('Device width px:${ScreenUtil.screenWidth}'); //Device width
    print('Device height px:${ScreenUtil.screenHeight}'); //Device height
    print(
        'Device pixel density:${ScreenUtil.pixelRatio}'); //Device pixel density
    print(
        'Bottom safe zone distance dp:${ScreenUtil.bottomBarHeight}'); //Bottom safe zone distance，suitable for buttons with full screen
    print(
        'Status bar height px:${ScreenUtil.statusBarHeight}dp'); //Status bar height , Notch will be higher Unit px
    print(
        'Ratio of actual width dp to design draft px:${ScreenUtil().scaleWidth}');
    print(
        'Ratio of actual height dp to design draft px:${ScreenUtil().scaleHeight}');
    print(
        'The ratio of font and width to the size of the design:${ScreenUtil().scaleWidth * ScreenUtil.pixelRatio}');
    print(
        'The ratio of  height width to the size of the design:${ScreenUtil().scaleHeight * ScreenUtil.pixelRatio}');
  }
}